wilbur - atlanta, ga | home

WILBUR SMITH

ASSOCIATES I ENGINEERS PLANNERS e ECONOMISTS

2990 BRANDYWINE ROAD c SUITE 125 ATLANTA, GA 303413529 * (770) 936-8650 * FAX (770) 936-8656

the device, and similarly, the existing roadway conditions that may limit the device's implementation.

We hope this document meets the needs of the City and its residents. Should questions arise regarding specific details of the traffic calming device implementation process, please do not hesitate to call me at (770) 936-8650.

-n 2 CRA GHANA * ALBANY, NY ANAHEIM, CA * ATLANTA, GA BALTIMORE, MD BANGKOK. THAILAND CARACAS, VENEZUELA * CHARLESTON, SC CHICAGO. IL CLEVELAND, OH COLUMBIA. SC COLUMBUS, OH * FALLS CHIJRCH, VA a HONOLULU, HI * HONG KONG HOUSTON, TX ISUN, NJ KUWAIT KNOXVILLE. TN EXINGTON, !iY LONDON, ENGLAND * MILWAUKEE, WI 0 NEW HAVEN, CT ORLANDO, FL - OVERLAND PARK, KS PHILADELPHIA. PA * PIITSBUSH, PA RALEIGH NC RICHMOND, VA SALT LAKE CITY, UTAH SAN FRANCISCO, CA SAN JOSE, CA TALLAHASSEE, FL * TAMPA, FL * TORONTO, CANADA WASHINGTON. DC

EMPLOYEE-OWNED COMPANY

Table of Contents

Introduction I

Data Collection Procedures for the Implementation of Traffic Calming Devices 3

Analysis And Evaluation 5

Priority and Ranking Procedure 8

Traffic Diversion and The Impact Threshold Curve 10

Traffic Calming Device Details

Procedural/Administrative/Regulatory Techniques

Turn or Entry Prohibitions 12 Neighborhood Speed Watch Program 13 Radar Trailer 14

Physical Techniques Horizontal Deflection Devices

Narrowing Treatments

Striping Treatments 16 Median Treatments 18 Curb Extension Treatments

One-Lane Slow Points 21 Two-Lane Slow Points 22 Curb Bulb-Outs 27

Weaving Treatments Chicanes 30 Serpentine 32

Vertical ~eflection-Devices

Rumble Strips 35 Road Humps 39 Speed Tables 45 Raised Intersections 47 Traffic Circles 49 Traffic Diverters

Turning Movement Diverters 54 Diagonal Road Closure/Diversion 56

Residential Neighborhood Gateway Treatments 57 Roadway Closures

Full Roadway Closure - 59 Partial Roadway Closure ' 61 Open Roadway Closure 62

Table 1 : Summary of Traffic Calming Device Characteristics 64

References 65

Introduction Traffic calming is an engineering methodology to physically change the character of streets, improving pedestrian safety and encouraging drivers to obey speed limits. Traffic calming utilizes a variety of physical devices to alter the geometry of the street, along with more traditional traffic engineering techniques to slow traffic. A S U C C ~ S S ~ U ~ traffic calming plan is (generally) not a single device, but rather a series of integrated improvements to slow traffic and, if desired, to direct traffic to more appropriate routes.

When concerns regarding traffic speeds, pedestrian safety, and cut-through traffic arise in residential areas, it is often frustrating for both residents of the area and traffic engineers. The .neighborhood often requests a quick fix solution such as enforcement, reduction in posted speed, or the addition of stop signs. This increases the pressure to implement a haphazard solution that may not be in the best interests of the neighborhood, the jurisdiction, or the travelling public.

The use of traffic calming devices must be carefully documented so that they are not used inappropriately, or too frequently. Jurisdictions should have in place a four-phased procedure by which traffic calming devices may be requested, evaluated for appropriateness, and implemented:

Documentation of the problem and the need for traffic calming devices; The collection of field reconnaissance and traffic study data; Selecting the proper device to correct the problem; and Monitoring the effectiveness of solving the problem once the device(s) are installed.

The City of Atlanta Department of Public Works 1 Traffic and Transportation's Neighborhood Traffic Management Program (NTMP), in place since 1985, provides administrative procedures that document and catalogue complaints from residents concerning neighborhood traffic-related problems.

This document builds on this process, assisting staff by providing a basis to objectively rank these requests for calming improvements in order of greatest need (here "need" is defined as the magnitude of the impact felt by residents of existing traffic conditions within a given neighborhood). In order to determine the need for traffic calming measures, traffic studies at the affected area must be conducted. Consequently, field data collection procedures, essential for the assessment of traffic conditions within a candidate area, are also detailed. Finally, the handbook describes a full range of traffic calming measures, the advantages and disadvantages of each, design considerations, and the general traffic conditions to which each is best suited.

It is the intention of the Atlanta Neighborhood Traffic Management Program to address traffic problems and concerns on local residential streets. While not intended to make streets play areas for children or adults, the NTMP is intended to generally improve safety for pedestrians, bicyclists, and others who travel along or across these streets.

Roadways classified as arterial and above are excluded from receiving traffic calming measures, as the primary function of these roads are for the movement of vehicular traffic. Roadways designated as collectors are excluded from the installation of road hump treatments, Generally, any treatments that divert traffic are not to be installed on streets designated as collectors. As well, there are other streets, (depending on their location and individual characteristics), that may not be eligible for the installation of particular types of traffic calming measures (for example, designated bicycle and emergency response routes).

Figure 1 depicts the neighborhoods of the City of Atlanta, as well as roads classified as collector and above (shown by functional classification). Planned designated bicycle routes are also shown.

City of Atlanta Trafffc Calming Device Implementation Guidebook

Rgure I : Neigh bwhoods, Roadways -Classified~ -

as Arterial or Above, including Bike Routes Planned for 1, 5, and 15 years.

Roadways Classified Arterial or Above Bike Routes Planned within 1 Year Wke Routes Planned within 5 years Bike Routes Planned within 15 years Atlanta Neighborhoods

Data Collection Procedures for the lmplementation of Traffic Calming Devices Before specific traffic calming treatments are chosen for an area or roadway segment, certain data collection procedures must be undertaken to gauge the specific nature of the traffic problem involved.

These procedures are divided into two phases:

Collecting field reconnaissance information, and The selection and conducting field studies.

Engineering Field Reconnaissance

Following appropriate contact with Traffic and Transportation, appropriate staff shall conduct a through reconnaissance of the neighborhood affected by the traffic problem(s) reported by the resident(s), and become acquainted with traffic patterns in a general way. Special attention will be given to the specific issues raised by neighborhood residents. Having completed this reconnaissance, specific study area boundaries will be established, and locations for spot speed studies, average daily traffic (ADT) counts, and turning movement counts (as appropriate) will be selected. Specific gateways to the area will be selected for any origin-destination (0-D) studies that may need to be conducted.

The field reconnaissance will also produce an inventory of traffic control devices (stop signs, yield signs, turn prohibitions, traffic signal locations, phasings and timings) that influence traffic movements into or through the neighborhood. The inventory should include all streets within the study area, as well as arterial or collectors that may be adjacent to it, serving as gateways to the neighborhood.

General attention will be oriented toward driver observation of such traffic regulations as speed limit signs and stop signs, with a special interest directed at resident reported problems of this nature. This reconnaissance will also look for physical obstructions or other conditions that would compromise motorist or pedestrian safety, given the posted speed limit.

Field Studies

The types of studies undertaken will be determined by:

' Reported complaints by residents, and ' The results of field reconnaissance.

The following table lists'traffic studies that will typically be undertaken to respond to the several general classes of traffic problems:

Excess Traffic Volume ' ADT Counts ' Turning Movement Counts ' 0 - D Study

Speeding ' Spot Speed Survey ' Accident Study

In some instances, an area's traffic issues may include more than one class of problem; this condition may increase the number and complexity of studies required. For instance, in some areas, it may be necessary to also conduct pedestrian and bicycle counts if they figure predominately into traffic conditions within the area.

The following sections describe the studies listed above:

City of Atlanta Traffic Calming Device lmplementation Guldebook

ADT Counts: These counts will be conducted in accord with Traffic and Transportation procedures. They should be taken for a period of not less than one weekday (24 hours). ADT counts should be taken along all identified problem streets, on neighborhood streets at gateways to the area, and on adjacent or nearby major arterials or collectors (as appropriate).

Turning Movement Counts: These manual counts are required when the principal neighborhood traffic problems result from through traffic. They will be conducted at intersections that serve as gateways to the neighborhood. In most circumstances, they can be restricted to the peak travel hours (7:OO - 9:00 a.m. and 400 - 6:00 p.m.). Should the field reconnaissance or neighborhood meeting reveal through traffic problems during other time periods, consideration will be given to extending the count period.

Spot Speed Survey: This survey is intended to measure the prevailing speed of traffic, and to determine the percentage of total motorists..who exceed the speed limit. It.will be conducted in accord with standard Traffic and Transportation procedures.

Accident Record Investigation: This involves a search of accident records to establish the frequency of occurrence at intersections within and on the fringe of the study area. It will also identify accident occurrence at mid-block locations within the study area. These studies will cover a period of at least one year (typically two years).

Origin-Destination (0-D) Studies: 0-D studies will be conducted when the basic traffic problem relates to excessive cut-through traffic on a particular residential street, or when the problem relates to truck movements through the area. The recommended procedure involves stationing two observers at each gateway to the neighborhood. One observer will record inbound activity and the other will record outbound activity. Information to be recorded includes the time of day (at one minute intervals) and the vehicle license number of all vehicles that enter or exit the neighborhood; license numbers and the time of day must be correlated. These studies will normally be made for a continuous two-hour period in morning and afternoon peak travel hours. For neighborhoods that have certain types of problems, 0-D surveys may be needed at other times of the day. It is necessary to use a sufficient number of surveyors to observe all gateways to the neighborhood simultaneously, if a full understanding and documentation of the through traffic problem is to be gained.

There are two methods available for recording the required data. These are:

Filling in the information on a standardized data form in the field, and

Recording the information into a hand-held voice recorder, and transcribing it on to the appropriate data forms later.

The selection of a method will depend largely on the volume and speed of traffic passing the survey station; some experience with each method will be required to establish threshold values for selecting the appropriate alternative. Field recording of information directly onto the data form is preferred, and can be accomplished when volumes are relatively low. For higher volume or speed levels, the time required to observe the license plate number and record it on the form may cause passing vehicles to be missed. Since voice recording of the information requires less time, this method is appropriate for higher volume streets.

Other candidate 0-D survey methods require that motorists be stopped and either asked a series of questions about their intended (or just completed) travel path, or given a unique card or token to be collected at a subsequent 0-D station. These methods are more disruptive to traffic movement, and could cause detours that would bias survey results. Such methods should be used only when the recommended procedures will not yield satisfactory results.

City of Atlanta Traffic Calming Device implementation Guidebook

Analysis and Evaluation The various data collected in the field reconnaissance and during the data collection effort will be summarized and analyzed to determine if a problem does or does not exist, by comparing actual activity measures to established threshold values. Threshold values are presented in the following sections for each of the basic types of traffic problems. It is emphasized that many of these suggested limiting values must be carefully weighed in the context of their application to problems within the study area. Moreover, experience gained in the future may suggest changes in these values to better relate to problem definition.

Traffic Volumes Analysis: There is much debate over ADT or hourly traffic volume threshold values on residential streets. A particular volume may be well below street capacity, yet intolerable to residents along the street. Past experience have shown that traffic flows less than 800 vehicles per day (VPD) are acceptable, and those above 4,000 vpd are excessive. From this, it can be determined that the threshold value for ADT is somewhere between 800 and 4,000.

Another consideration of tolerance levels for ADT along residential streets relates to a resident's difficulty in leaving the driveway for a trip away from home. This maneuver usually involves backing a .vehicle into the street. Assuming a two lane, two-way street, and an acceptable gap length of 15 seconds to complete the backout maneuver safely, the probability of having to wait for one or more vehicles to pass can be calculated for various hourly volume levels. The average waiting time for the delayed vehicles can also be determined:

The peak-hour volumes shown above represent ADT's ranging between 1,000 and 4,000 VPD (assuming a 10 percent peak hour component). The probability of having to wait exceeds 80 percent at volumes of 4,000 VPD, and the average waiting time is about 43 seconds. This exceeds the waiting time at many signalized intersections (operating at acceptable levels of service). For the purposes of evaluation, average waiting times of over 15 seconds will be deemed unacceptable.

Two-Way Peak-Hour Volume (Vehicles per Hour)

100 150 200 250 300 350 400

Traffic volume should not be considered as a single criterion in evaluating neighborhood problems that include excessive volume. It is often found that a residential street will have relatively high volumes, yet experience little or no through traffic. Conversely, some residential streets have been observed to have through traffic components considerably in excess of 50 percent, even when total volumes are at an acceptable level. Thus, through traffic percentage alone does not offer a satisfactory measure of tolerability.

The likelihood that application of traffic calming measures to a residential area will have negative impacts as well as positive consequences suggests that existing problems will have to be judged as rather sever (by the neighborhood residents) for any consensus to be reached as to the acceptability of traffic calming plans. For instance, one jurisdiction may find that neighborhood consensus is difficult to achieve unless ADTs are in excess of 4,000 VPD and the through traffic component exceeds 40 percent. This suggests that volumes below 400 durin,g the peak hour are acceptable, when compared with the adverse impacts of measures required to reduce the flow rate. It also suggests that anticipated reductions in flow rates of less than about 150 vehicles per hour (2.5 vehicles per minute), may not be considered to be significant, when related to probable negative impacts.

Probability of Having to Wait (Percent)

34 46 57 65 71 77 81

Cify of A tlan fa Traffic Calming Device Implementation Guidebook

Average Waiting Time (Seconds)

12.0 15.3 17.5 21.6 25.7 32.3 42.8

These diverse findings suggest that tolerable limits for traffic volumes/through traffic components are not easily defined, nor is there a consensus as to what constitutes too much traffic. Therefore, a standard will be defined, and carefully monitored to appraise its applicability and acceptance. The suggested criteria are depicted in Figure 2. It incorporates total traffic volume during the peak hour and the percent of through traffic. Two threshold value curves that reflect through traffic components of 2.0 and 2.5 vehicles per minute, respectively divide the chart into three areas (tolerable condition, moderate problem and severe problem). Observed combinations of volume and through traffic percentages that fall below the lower curve will be classed as tolerable conditions; problems are not considered severe enough to warrant the application of traffic calming devices.

TWO-WAY VOLUME DURING PEAK HOUR

Figure 2: Criteria for determining severity of through traffic problems.

Existing conditions that fall between the two curves will be considered moderate and subject to the application of appropriate traffic calming measures if anofher type of traffic problem also ' exisfs, (i.e., speeding). Streets that portray combinations of volume/through traffic percentages above the higher curve will be considered intolerable to the extent required to warrant the application of traffic calming measures to reduce the volume of through traffic.

Speeding Analysis: Speed limits have been posted along most of Atlanta's residential streets. Posted limits of 25 and 30 MPH are fairly common. Past experience has shown that some

City of Atlanta Traffic Calming Device Implementation Guidebook

speeding will likely occur in most, if not all situations. Accepted procedures for determining the safe operating speed along an unposted st!;et includes measurement of prevailing speeds, and considering posting a limit at or near the 85 percentile speed.

Neighborhood concerns about speeding problems appear to be oriented to those motorists whose speed is significantly higher--generally more than 10 MPH--over the posted limit. Such speeds are the main cause of concern, and usually are the ones that create accident potential. Moreover, speeding problems should generally prevail throughout seiieral blocks of a street or along several streets of a neighborhood for the problem to be considered for traffic calming treatments.

The criteria to be used to determine th~~presence and seriousness of speeding problems is given in Figure 3. It relates the observed 85 percentile speed to the posted speed limit. If the speed studies reveal the 85th percentile speed to be equal to or less than the posted limit, a tolerable condition will be found to exist. Actions to reduce the prevailing speed are generally not considered to be warranted when the relationship between the 85th percentile speed and the posted speed limit is below the lower threshold line on the chart.

b

20 I

26 3d 35 40

POSTED SPEED LIMIT (MPH)

Figure 3: Criteria for determining presence and severity of Speeding problems.

When the 85th percentile speed exceeds the posted speed limit, it will be concluded that a speeding problem exists. The problem will be classed as "moderate" if the 85th percentilelposted speed limit comparison falls between the two threshold lines on Figure 3 and "serious" when the comparison exceeds the upper threshold value line. Often, jurisdictions will adjust the posted speed limit based upon the percentage of motorists travelling (usually 10) mph over the 85th percentile speed, based on spot speed study evaluations. City of Atlanta Traffic Calming Device implementation Guidebook

Priority and Ranking Procedure

Procedures for determining the presence and severity of speeding and cut-through traffic have been discussed, yet there is often a need to prioritize many different requests for traffic calming measures in areas where need has been determined. The following sections discuss a proposed process, based on the presence and severity of speeding and cut-through traffic, and a points system.

Priority will be assigned to candidate roadway segments in the following manner, based on data collected from the field and Figure 2 and 3. (Note: Those roadway segments with high pedestrian counts and/or .activity will automatically be given high priority).

For roadways that prioritize equally based on this scheme, the following points-based ranking system will be used to differentiate between candidate roadway segments.

Speed-The speed score will be based on the 85th percentile speed and the posted speed limit. On road segments where the 85th percentile speed exceeds the posted speed limit by 10 mph or less, no points will be assigned. For every mph (above 10 mph over the'posted speed limit) that the 85th percentile speed exceeds the posted speed limit, 2 points will be assigned.

High Priority

Middle Priority

Low Priority

Traffic Volume-Volume will be based on average daily traffic (ADT). Up to 25 points can be assigned (1.667 points per 1,000 ADT, up to a maximum of 25 points for 15,000 ADT). (1.667 is used for a scaling factor, so that 15,000 ADT will yield 25 points).

Volume Condition

Accident Rate-Here a weighted score is determined that equals the number of accidents on the roadway segment in question, multiplied by 1,000,000 vehicle miles traveled (this is done to generate an accident rate so that different segments may be compared.

Speed Condition

Moderate

This is divided by the product of the following: The number of days for the period of accident observation, the length of the street segment (in miles) and the ADT for that street segment. For example, if a street segment 0.18 miles long with 1850 ADT had 5 accidents over a year,

Moderate Severe

Accident Rate = [(Total Accidents * 1,000,000)] 1 [(#days observed * length (miles)) * (ADT)]

Severe

= 41 1.37 accidents I Million Vehicle Miles Traveled

One point is assigned per 100 MVMT


Residential Density-Residential density will be determined based on zoning. All buildings with frontage on the street segment will be included. Both single- and multi-family residential will be considered. (One point will be given for each dwelling unit that has frontage along the street segment in question. Multi-family dwellings will receive 1 point for each 5 dwelling units contained within).

Lack of Sidewalks-Street segments lacking sidewalks will be given 9 points. The lack of sidewalks is defined as the absence of a C O ~ ~ ~ ~ U O U S sidewalk on both sides of the street segment. Selection of these streets does not necessarily mean that sidewalks will be built as part of the project.

Elementary Schools-Street segments will be assigned 7 points if there exists an elementary school with any frontage on the given segment.

Other Pedestrian Generators-Street segments will be assigned 5 points if any of the following pedestrian generators occur within the street segment (i.e., from arterial to arterial) and within 1,000 feet of the street:

Retail commercial uses.

a Institutional uses.

Parks.

Other schools not included in the elementary school crossing criterion (e.g., middle, high schools).

Bicycle Routes-Any street identified as being along a bicycle route by the city will have five points deducted from the total.

Street Width--Street segments over 40 feet wide will be given 4 points.

City of Atlanta TraHc Calming Device Implementation Guidebook

Traffic Diversion and the lmpact Threshold Curve

The lmpact Threshold Curve has been established to provide a tool to help determine if the unintentional impacts of traffic-calming projects on local streets are acceptable. In most cases, these impacts are in the form of increased traffic on adjacent streets. The lmpact Threshold Curve identifies a range of traffic diversion that is typically considered as acceptable. lmpact limitations are expressed as a curve because the level of impact that is considered allowable will vary, depending on the characteristics of the street affected by the project.

The following guidelines are used in establishing numeric impact limitations on non-project local streets (Here a maximum volume of 3,000 VPD is used for example purposes. As will be mentioned, this value may be adjusted for Atlanta's maximum of 4,000 VPD for local streets.)

1. The standard curve is expressed in terms of total traffic volume (i.e., vehicles per day-VPD). The parameters of the curve are as follows:

a) There is a threshold of at least 150 VPD. This means that an increase of 150 VPD as the result of the installation of a traffic calming device is acceptable on any local street (subject to the restrictions in "c" below), regardless of its prior volume.

b) There is a maximum acceptable increase of 400 VPD. In other words, an increase of more than 400 VPD is not acceptable on any local street.

c) The resulting traffic volume on any local street should not exceed 3,000 VPD.

d) Using a spreadsheet and a set of formulas, these parameters are used to establish a standard lmpact Threshold Curve.

2. Because of the margin of error inherent in the collection of volume data, the curve is presented as a wide band or range, rather than a specific line. This allows the margin of error to be accommodated within the range. Therefore, two supplementary curves, one on either side of the standard curve, are used along with the'standard curve. These "margin or error" curves are * 50 VPD, or 10% of the measured pre-test volume, whichever is greater.

The "standard" curve then becomes the "median" curve within a range. An increase in traffic volume that falls between the median curve and the lower curve would probably be acceptable. An increase that falls between the median curve and the upper curve would possibly be acceptable. An increase that falls above the upper curve would clearly not be acceptable.

3. The "standard" curve may be modified for application to a particular traffic calming device installation based on the following:

a) The ratio of local to non-local traffic on the project street and adjacent streets.

b) The percentage of the re-routed traffic that is local versus non-local.

c) The preexisting traffic volume on the project street.

City of Atlanta TrafRc Calming Device Implementation Guidebook

d) The proximity of arterial routes that can absorb re-routed traffic

e). Peak-hour volumes.

f) Truck traffic.

Modification to the "standard impact curve would automatically result in adjustments to the upper and lower "margin or error" curves.

An impact threshold curve is not the only tool for judging whether a project's impacts on adjacent streets is acceptable. An increase in traffic volume that exceeds the Impact Threshold Curve

.. , .

does not constitute a fatal flaw to the project unless Traffic and Transportation makes that determination prior to project implementation. Other, more qualitative criteria may also be used to help determine whether a project's secondary or unintended impacts are acceptable. If it is found that the impacts are unacceptable, these impacts should be appropriately mitigated. Mitigation may include a neighborhood stop sign plan, installation of road humps, or possible removal or the speed humps causing the diversion.

ACCEPTABLE INCREASES IN TRAFFIC VOLUME ON NON-PROJECT STREETS

925 1 350 1775 2200 Vehicles per Day -- Pre-Test

Figure 4: The Impact Threshold Curve. . .

Cify of Atlanta Trafnc Calming Device Implementation Guidebook

Traffic Calming Device Details

Procedurall~dministrativelRegulatory Techniques Regulatory measures have been the conventional method for dealing with neighborhood traffic concerns. The following pages present a short discussion of these measures.

Turn or Entry Prohibitions

Description: Used to prohibit particular turning movements onto local or collector streets. Turn or entry prohibitions seek to reduce traffic volume, particularly cut-through volume travelling through local neighborhood streets.

Advantages:

@ Inexpensive

Disadvantages:

Difficult to enforce Driver confusion Resident inconvenience Traffic diversion to other streets

City of Atlanta Traffic Calming Device Implementation Guldebook

Neighborhood Speed Watch Program

Description: Jurisdictions that maintain neighborhood speed watch programs typically make available a hand-held radar gun, (with staff instruction) to neighborhoods whose residents then determine the amount of speeding, and identify who is speeding within the neighborhood. For example, a resident or group of residents meets with city staff in the neighborhood and instructions are given to the use of the radar gun. The resident then spends several hours registering the speed of cars passing on the street. The residents have a first hand account of whom the speeders are and how fast they are going. The City of Atlanta does not currently have a neighborhood speed watch program in effect.

Neighborhood speed watch programs are essentially public-relations campaigns that need considerable resources in order to be effective. The City of Portland, Oregon, for instance, budgeted $50,000 in FY '94-95 for their speed watch program. As part of the process, speeding motorists (as recorded by residents) are sent letters from the Oregon Department of Transportation informing them of the speed watch program and the impacts of their driving behavior on local neighborhoods. Additionally, police enforcement must supplement the speed watch observations of residents in order to truly be effective. Not all jurisdictions have the police resources to support this task. Through it all, secretarial and support staff must be maintained in order to track resident's speed observations and maintain correspondence.

Advantages:

May have long-term effects as neighbors become more aware of who is speeding then interact with each other.

Effect on speeders is limited to within sight distance of the radar gun. Speeds may be reduced during short intervals when the radar gun is in use. Can be an effective public relations and educational tool. Residents feel they are part of the solution.

Disadvantages:

Not an enforcement tool (if not used in conjunction with police enforcement). Can cause conflicts between neighborhood residents. Can require inordinate staff and financial resources in order to be effective.

Not effective on multi-lane roadways that have significant traffic volumes. In these cases, there is limited ability to differentiate between more than one approaching vehicles.

City of Atlanta Traffic Calming Device lmplementafion Guidebook

Radar Trailer

Description: A portable radar speed meter capable of measuring vehicle speed graphically and displaying the speed of a motorist to the driver in question.

Advantages:

' Speeds may be reduced during short intervals where the radar trailer is located. ' An effective public relations and educational tool.

Disadvantages:

' In and of themselves, radar trailers are not enforcement tools. Effectiveness may be increased through periodic supplementation by police enforcement.

Trailers are not effective on multi-lane roadways having significant traffic volumes. In these cases there is limited ability to differentiate between more than one approaching vehicle.

The City of Atlanta Police Department currently uses radar trailers to aid in calming traffic within residential neighborhoods.

City of Atlanta Trafnc Calming Device lmplementatlon Guidebook

PHYSICAL TECHNIQUES

Physical techniques to calm traffic can be placed into one of two broad categories: Horizontal or Vertical deflection devices. Where appropriate, physical traffic calming techniques are often constructed with colored andlor textured block paving. The use of paving materials such as brick, cobbles, blocks or concrete pavers create variation in color and texutre on the driving surface. This reinforces the identity of the area to the driver as a traffic-restricted zone, where pedestrians and bicyclists have greater priority. Depending on how tactile the chosen surface is, speed reductions may even be possible with the installation of these materials.

However, some pavers and texturing can be slippery or otherwise cause loss of steering control under some conditions. Where the surface material is too rough, bicyclists may move onto alternative, busier roads, or onto the adjacent pavement. This increases the likelihood of conflict with pedestrians. Also, the more textured the surface, the noisier it is. On the other hand, if the surfaces are not textured enough, then their traffic calming value is limited.

Whatever the surface used, colored andlor textured paving should only be used as part of a larger, overall traffic management plan for a given street or streets.

Horizontal Deflection Devices

In the past, streets have generally been designed to accommodate traffic with minimal interruption, which often leads to wide, long, straight streets. The effect of a wide, long, straight street without visual interruption is to encourage speeding. In general, the wider and straighter the street, the faster drivers will travel. Horizontal deflection devices serve to either narrow the roadway (narrowing treatments), or break up the long, straight nature of some local streets (weaving treatments), thereby reducing speeds. The following outlines the collection of horizontal deflection devices detailed:


Striping Treatments Median Treatments

Curb Extension Treatments One-Lane Slow Points Two-Lane Slow Points Curb Bulb-Outs

Weaving Treatments Chicanes Serpentine

City of Atlanta Tramc Calming Device Implementation Guidebook


Striping Treatments

Description: Striping is used to create narrow, 10-foot wide lanes. This gives drivers the feel of a narrow street that does not lend itself to high speeds.

Advantages:

Changes can be quickly implemented. ' The striping can be easily modified if paint is used.

' Speed may decrease and safety is improved through the provision of positive guidance to drivers.

Disadvantages:

Would increase regular maintenance. ' Residents do not always perceive striping as an effective tool for speed reduction.

Cost of resurfacing residential streets will increase.

Design Considerations:

Striping more than 5 feet from the shoulder or curb will require hatching treatments to be utilized. Otherwise, drivers will use the striped off area as part of a lane. Striping may also be provided for on-street parking stalls.

Figure 5: Striped bicycle lanes narrow the traveled roadway.

City of Atlanta Trafnc Calmlng Device Implementation Guidebook

As well, the striped off lane may be designated for the use of bicyclists. There are several advantages to both motorists and cyclists.

Benefits to bicyclists:

' Bike lanes permit bicyclists to advance to the intersection when traffic is backed up. ' Bike lanes provide lateral separation from motor vehicles.

@ Bike lanes reduce the number of lane shifts and changes needed by the bicyclist, allowing the rider to concentrate on motorist behavior and actions.

' Bike lanes reduce the number of bicyclists who use the sidewalk. This shift can reduce carlbike crashes at intersections.

Benefits to motorisfs: (Since on a retrofit the bike lanes may force travel and turn lane width reduction, justification is often needed.) When provided, bike lanes often help the motorist by:

' Reducing bicyclistlmotorist conflict. ' Making bicyclists more visible and predictable ' Increasing physical separation ' Allowing motorist to pass bicyclist legally and safely. ' lmproving turn radii into and out of driveways and intersections. ' Reducing travel lane encroachmentlsideswiping rear ending type crashes. ' lmproving flow rate.

City of Atlanta Trafnc Calming Device Implementation Guidebook

Median Treatments

Description: Medians are islands located along the roadway centerline, separating opposing directions of traffic movement. They can be either raised or flush with the level of the roadway surface. They can be expressed as pavement markings, raised concrete platforms, landscaped areas, or any of a variety of design forms. Medians can provide special facilities to accommodate pedestrians and bicyclists, especially at crossings of major roadways. Median treatments often incorporate colored or textured block paving, especially if flush with the roadway. If raised, such treatments are referred to as islands. Island barriers that are of adequate size for pedestrian use are often referred to as refuges.

Advantages:

Crossing of major roadways is divided into two shorter segments. Pedestrians and bicyclists must scan in only one direction at a time. Gaps are generally more frequent, as only one direction of traffic flow is crossed at a time.

May reduce vehicle speeds, especially with other traffic calming devices. Safety and visibility of pedestrian crossing points are enhanced. Visual break or screen along line of roadway is created. Can be installed at intersections, or mid-block. Visual enhancement, particularly if landscaped. May prevent passing at pedestrian crossings if used with a slow point.'

Generally limited reduction in vehicle speeds, unless used in conjunction with roadway narrowing or other traffic calming devices.

* Used in conjunction with slow points, medians are limited by AASHTO standards for transition taper length.

Sometimes limited by parking removal issues, Can be expensive, particularly if landscaped. Access and movement of motorists are prohibited and/or limited.


Medians are most valuable on major, multi-lane roads, which present safety problems for bicyclists and pedestrians wishing to cross. The minimum central refuge width for safe use by those with wheelchairs, bicycles, baby buggies, etc. is 1.6 meters (2 meters desirable).

Where medians are used as pedestrian and bicyclist refuges, the installation of bollards is suggested to facilitate quick and easy identification by motorists, bicyclists and pedestrians.

Used in isolation, roadway medians do not have significant impacts in reducing vehicle speeds. For the purpose of slowina traffic, medians are generally used in conjunction with other devices such as curb extensions.

To achieve meaningful speed reductions, the travel lane width reduction must be substantial- and visually obvious. The slowing, however, is temporary; as soon as the roadway widens after the narrowing, traffic resumes its normal speed.


Bicyclists have been put at risk of being squeezed where insufficient room has been left between a central median and the adjacent curb. Experience shows that most drivers are unlikely to hold back in such instances and let bicyclists go first. This is a threat particularly serious on roads with high proportions of heavy vehicles.

The contradiction between the need to reduce roadway width sufficiently to lower motorist speeds while at the same time leaving enough room for bicyclists must be addressed. This may be achieved by reducing the roadway width to the minimum necessary for a bicyclist and a motorist to pass safely (3.5 meters) and also:

-- Introducing textured and/or colored paving to the road surface material around the refuge area to remind motorists that speed reduction is intended;

-- Giving the visual impression (through white striping, for example) that vehicles are confined to a narrower roadway than that created by the physical obstruction, or that adjacent areas exist which vehicles can run over (but are not generally apparent to approaching drivers; or

-- Providing an alternate, cut-through route for the bicyclists in some cases.

Figure 6: A refuge island median treatment, with bollards installed.


~ i ~ u r e . 7 : The technical drawing specifying the refuge island median treatment specified in Figure 6.

Figure 8: A median treatment allowing left turns at a 4-legged intersection. , .


Curb Extension Treatments

Description: Curb extensions curb toward or to the traveled particular design form makes

(sometimes referred to as curb build-outs) are extensions of the way. They may be installed at intersections, or at mid-block. Their them a building block for a variety of different traffic calming

treatments.

Curb extensions placed at opposite sides of each other along the roadway are called "chokers," "pinch points," or "slow points." Slow points narrow a two-way road over a short distance. Depending on the width of the roadway (and of the curb extension), slow points can be either one- or two-lane. Oftentimes, curb extensions are used at intersections to create a "semi- diverter," used in the design of partial roadway closures (see p. 61) The following sections discuss slow points, and another application of curb extensions, curb bulb-outs.

One-lane slow points

Description: One-lane slow points restrict traffic flow to one lane. This lane must accommodate motor traffic in both travel directions. Passage through a one-lane slow point is straight. A priority traffic direction is established, with prudent design incorporating signage that conveys information concerning traffic flow priority direction to the driver.

Advantages:

Vehicle speed reduced. Most effective when used in a series. - Imposes minimal inconvenience to local traffic. Pedestrians have reduced crossing distance, greater safety. Provides space for landscaping. Provides a visual obstruction.

Disadvantages:

Can be hazardous for drivers and bicyclists if not designed and maintained properly.

Reduced sight distances if landscaping not low .and trimmed. Unobstructed flow does not meet driver expectancy. Opposing drivers arriving simultaneously can create confrontation.

Figure 9: A one-lane slow point.


Two-lane slow points

Description: Two-lane slow points narrow the roadway, while providing one travel lane in each direction. Passage through the slow point may be straight- through, or angled.

Advantages:

Regulates parking and protects parked vehicles as the narrowing can help stop illegal parking.

Only minor inconvenience to drivers. Pedestrian crossing distances reduced. Space for landscaping provided


Where slow points have been used in isolation as speed control measures, bicyclists have felt squeezed as motorists attempt to overtake them at the narrowing. Not all bicyclists have the confidence to position themselves in the middle of the road to prevent overtaking the approach to and passage through the narrow area.

To reduce the risk of bicyclists' being squeezed, slow points should generally be used in conjunction with other speed control devices (such as speed tables) at the narrowing. Slower-moving drivers will be more inclined to allow bicyclists through before trying topass, Where bicycle flows are high, consideration should be given to a separate right-of-way for bicyclists past the narrow area.

Using textured andlor colored surfaces such as brick or pavers may emphasize pedestrian crossing movement. Substituting this for the normal roadway surface material may also help to impress upon motorists that lower speeds are intended.

Such measures should not confuse pedestrians with' respect to the boundary of the roadway area over which due care should still be taken. In particular, irt cases where a road is raised to the level of the adjacent sidewalk, this can cause problems for those with poor sight. However, a tactile strip may help blind people in distinguishing between the roadway and the sidewalk; similarly a color variation will aid those who are partially sighted.

Slow points can be used to discourage use of the street by large vehicles. They can, however, be barriers to fire trucks and other emergency vehicles, particularly when bollards are used. Some designs permit access by emergency vehicles by means of lockable posts or ramped islands.

Slow points can enhance the appearance of the street. For example, landscaped islands can be installed, intruding into the roadway to form a narrow "gate" through which drivers must pass. Landscaping enhances the neighborhood's sense of nature and provides a visual break in views along the street.


.6u!~oueu ayljo uo!vod Val aw uo pallelsu! s! a6eu6!s MOU qjp~.l) rtuo!~d 'lu!od-~ols A ~ M auo v : 11 a1n6lj

Standard pinch point * Nole: R o l h - P d kzw I. bc

vll*d .'ah Llurhan mc&,,,

wial r n ~ tsni WS.

Single side build out

Figure 12: Technical drawings for th4 type of curb extensions shown in Figure 11. Both single-side and standard slow points are shown.

Figure 13: A one-way narrowing with ''cycle slipsn (accommodations for bicyclists), and bollards (posts, here marked in red and white, that are often incorporated into traffic calming schemes. Bollards serve as vertical obstructions that help to slow traffic.) A "speed

in the center of the scheme (see p. 44 for a discussion of speed cushions). Priority traffic flow directional signing has not been installed.


@ G , S c * p E D @ ;,rdSORY SPEED DRIVE I WAY I

@ IJOUNTABLE RETROFLEtTlVE n KERB SECTIOIJ PAVEMENT MARKERS

H A Z A R D MARKEG ,, PARKlldt RESTRICTION @ HE? 5 (R) N O STANDING ANYTIME

Figure 15: A technical drawing depicting a two-way angled slow point.

Figure 16: A two-lane angled s l d i point. Nqte the differences between'it and the one pictured in Figure 15. The addition of a median barrier to a two-lane angled slow point helps maintain steady passage through

it. Ottietwise, motorists arehesitant to enter the angled slow point while-another vehicleis occupying it.


Curb Bulb-Outs

Description: Bulb-outs are a type of curb extension that narrow the roadway width at an intersection by modifying the curb return, providing a physical constraint at an intersection which forces motorists to slow down in order to pass through the narrower roadway section. This measure is typically constructed at intersections.

This type of measure offers speed reductions at the point of the measure, as well as a visual break along long stretches of roadway to make the roadway appear either shorter, or not as a through route.

Advantages:

Visual traffic calming effects and point speed reductions Highlights intersections for motorists. Reduces length of crossings for pedestrians. Provides opportunities for landscaping No adverse effect on emergency vehicle access.

Disadvantages:

Storm drain, street lighting, sewer, and other utilities may be affected and require relocation.

Reduces available on-street parking spaces. Forces bicyclists into the. travel lane with motorizedvehicles.


Bulb-outs are beneficial on long, straight, and flat roadway sections where a break-up of a"runway effect" may be necessary. Due to pedestrian benefits, consideration should be given to high pedestrian use intersections (adjacent to schools, commercial centers, etc.) Design considerations include accommodating large vehicles (fire trucks, garbage trucks, moving vans, etc.), street lighting, maintaining drainage system, allowing bicycle access, and landscaping and the associated maintenance and sight distance issues. It is beneficial to include lighting if not already in place at the candidate intersection for curb bulb-out installation.

Figure 17: A typical curb-bulb out scheme at an intersection.


.iuawuo~!~ua ue!J)sapad laps e aieaJ3 se llaM se 'wayi J O . ~ ~ ! U ! ~ ! A ayi u! q ~ e ~ i MOIS 01 papuaiu! 'sino-pl!nq

qJn3 a6~el St3 40 iy6noqi aq Ue3 SUMOpy3aN .UMOpy33U e 40 aldwexa U v :6C a ~ n 6 ! j

Figure 20: Shortening corner radii at intersections can have the same effect on traffic speeds as installing bulb-out treatments- This figure shows the relationship beween mmer radii and turning

movement speed at an intersection.


Weaving Treatments

Street weaving consists of introducing a horizontal curvature to the roadway to break up the "runway effect" of wide, straight streets, requiring drivers to slow down and drive around the curve. Weaving treatments usually involve the placement of chicanes. Other weaving treatments include a serpentine, where the actual alignment of the roadway is a series of reverse curves.

Chicanes

Description: Chicanes consist of curb extensions, parking bays, street furniture, landscaping, or other physical obstructions along a straight roadway

Advantages:

The City of Seattle has experimented with chicanes for neighborhood traffic control. A demonstration project has shown:

-- A reduction of traffic volumes on the demonstration streets; -- Little increase in traffic on adjacent residential streets; -- Reduced motor speeds and collisions; and -- Strong (68%) support for permanent installation of chicanes by

residents.

Disadvantages:

The combination of a narrowed roadway, a tortuous route and reduced sight lines has generally proved successful in encouraging lower vehicular speeds and deterring through traffic. Bicyclists, however, have felt squeezed where the siting of a chicane has significantly reduced the roadway width and motorists then attempt to overtake on the passage through the chicane.

Chicanes have been viewed as obstacle courses by some reckless drivers. Sharp acceleration and braking are used to negotiate the obstructions which intimidate and endanger bicyclists and pedestrians.

Design Considerations .

Consideration should be given to safe bicycle travel- Bicycle bypasses and signs to indicate directional priority are suggested.

A reduction in sight lines should not be used in isolation to reduce speeds, as used alone this could be potentially dangerous. A reduction in sight lines may be appropriate to avoid excessive land taking or as a reinforcing measure only where other physical features are employed which reduce speed.

Chicanes offer a good opportunity to make environmental improvements through planting. However, preference should be given to low-lying or slow- growing shrubs to minimize maintenance and ensure good.visibility.

Measures should be employed to ensure that chicanes are clearly visible at night.

Where full closure (p. 59) or road humps (p. 39) are not feasible, chicanes may be used to reduce traffic speeds.


Figure 21 : Chicane treatment with bollards installed.

TRANSVERSE SECTION FROM ONE S I N

Figure 22: The technical drawings for the chicane scheme pictured in Figure 21.


Figure 23: A chicane treatment (with bollards installed).

Serpentine

Description: Roads can be designed to meander or jog sharply, slowing traffic and limiting views to discourage speeding.

Advantages:

Safety Improvement. Vehicle speedsreduced. Passing of turning vehicles prevented. Creates visual break or screen along line of roadway. Cut-through motor traffic reduced.

Disadvantages:

Possible increase in noise. Possible negative impact on bicyclists. Significant on-street parking removal. Bicyclists wishing to minimize the length of their journey mayalso avoid these routes. Requires major deviation from straight-line path. Straight-line deviation provides head-on and fixed-object collision potential.


. Serpentines roads are generally planned as part of the design stage of a new road layout, rather than superimposed on an existing layout. The siting of buildings is used to create a meandering road.

Designers should be aware of the need for accessibility to residential properties, both in terms of servicing as well as the needs of the individual. Serpentines will prove unpopular if they severely restrict accessibility.


Vertical Deflection Devices

Vertical deflection devices such as road bumps, road humps, speed tables, raised crosswalks and raised intersections are probably the most frequently identified techniques associated with traffic calming. These techniques can be very effective and are popular with residents wishing to control speeds within their neighborhoods.

Generally, all these techniques raise the road surface by approximately four to six inches over a short distance (rumble strips, or road "thumps") to approximately a car length (road hump or speed table). These measures typically improve pedestrian safety, reduce vehicle speed and may reduce through traffic to some degree. However, these measures can have negative effects on emergency vehicles. Consequently, they should not be used on designated routes for emergency vehicles.

Early consultation with emergency service agencies is extremely important before planning the implementation of a traffic calming scheme which incorporates any vertical deflection device. In some situations, it may possible or even desirable to achieve an effective scheme without the use of vertical deflections. The following outlines the collection of vertical deflection devices detailed:

Rumble Strips Fioad Humps Speed Tables Raised Intersections Traffic Circles

Traffic Diverters Turning Movement Diverters Diagonal Road Closure/Diversion

Residential Neighborhood Gateway Treatments

Roadway Closures Full Roadway Closure Partial Roadway Closure Open Roadway Closure


Rumble Strips

Description: Rumble strips consist of a pattern of raised markers (either ceramic or bituminous pavement) applied to the roadway in order to alert motorists of a change in roadway conditions ahead. They transmit vibration and sound to the motorists which refocuses attention back to the roadway. On newly constructed roadways, rumble strips may be cut directly into the pavement.

Advantages:

Rumble strips can provide advance warning of a change in neighborhood characteristics ahead. For instance, it can be used in conjunction with gateway treatments, striping changes, etc. to alert motorists that they are entering an area where they should drive with caution.

Rumble strips can also create an area with an uncomfortable roadway surface which may influence motorists to drive more slowly.

Disadvantages:

The noise and vibration created by the rumble strips affects adjacent residences. Bicyclists and motorcyclists may experience difficulty riding over the ceramic markers. Motorists tend to swerve to avoid driving over the rumble strips. Influence on motorists may be minimal, or site-specific.

The noise created by the device can cause residents to complain, and lead to the eventual removal of the strips.

INALL RUMBLE STRIP

XX= STOP AHEAD SLOW SCHOOL XING PEO XING

- CENTERLINE

STREET A

Figure 25: Technical Drawing depicting Rumble Strip Installation.


eC.QIeaCC@eYiC +q*Wfe \

1 \-- TYPE "A"

PAVEMENT

DIRECTION OF TRAVEL

NOTE: DIMENSIONS ARE CENTER TO CENTER

RUMBLE STRIP DETAIL

MARKERS

TYPICAL RUMBLE STRIP INSTALLATION

Figure 26: Technical drawing depicting rumble strip details.


v-v Y.IIa.S

.II*. "I.IUO* *I

P.Y,"l.l PU. *.IUW .q e l S9I.I

.ZI ID r lsuel u n w l r u r vu. ~1 &.~.u~rond. 01 !no eq 01 .q,.x * Y

Figure 29: The raised yellow device is a thermoplastic "thump." Thumps are deslgrled to be less obtrusive than conventional road humps, quieter than rumble strips, and less jarring than road bumps.

' Detail of Thermoplastic Road Thump b 1

'1 9' 5" Radius

, .

Figure 30: A technical drawing of the thermoplastic thump shown in Figure 29.


Road Bumps

Description: Road bumps (or "speed bumps") are abrupt raised areas in the pavement in a distance of one to two feet, and are generally designed to be traversed at 5 to 10 mph. They are typically used in parking lots as a speed control device. Road bumps are not appropriate for public roadways and are not recommended for use.

Road Humps

Description: A road hump (or "speed hump") is a raised area in the roadway pavement surface extending transversely across the roadway. Road humps are less abrupt than road bumps and can have rounded or flat tops. Flat-top humps incorporate angled ramps, and generally feel less abrupt, than round-top humps that are parabolically curved. Road humps normally have a maximum height of three to four inches and a travel length of approximately twelve feet, though these dimensions may vary. As part of the Neighborhood Traffic Management Plan, the City of Atlanta currently has in place a speed hump installation program. Under the criteria of this program, no hump treatments are to be installed on roads classified as collectors.

Advantages:

--" ga-&*

Figure 31: Road bumps vs. Road humps

Vehicle speeds decrease at individual humps, and between humps in a series without increasing accident rates.

Humps can achieve desired results on vehicle operations without imposing unacceptable safety risks, since design and placement guidelines have evolved from extensive engineering, testing and research.

Accidents generally remain stable or decrease; speed humps have not been found to pose a safety hazard when properly designed and installed.

A rocking motion is created that results in most vehicles slowing to 15 miles per hour or less at each hump and to 25 to 30 mph between properly spaced humps in a system.

Speed and traffic volume reductions attributable to humps tend to remain constant over time.

The majority of residents along a street where road humps are installed typically support their continued use.

A visual impression that the street is not intended for speeding or cut-through traffic is created.

Humps represent a largely self-enforcing method of slowing traffic.


Disadvantages

Potential slowing of emergency and service vehicles. Road humps have been used to deter trucks and other large vehicles from using particular streets.

Potential hazard for bicyclists

Increased vehicle noise

Potential diversion of traffic to other streets, especially if the street is being used as a shortcut or to handle overflow traffic from congested collectors or arterials. Volume reductions are affected by the number and spacing of humps and availability of alternate routes.

On-going maintenance costs.

Inconvenience for residents.

Street maintenance functions may be affected.

May be considered unsightly. However, this effect may be mitigated by the construction of humps with colored andlor textured materials.


If mid-block pedestrian crossings exist or are planned, they can be coordinated with speed '

hump installation since vehicle speeds will be lowest at the hump and pedestrians can then cross without having to negotiate ramps or curbs between sidewalk and street.

The humps must be visible at night.

Humps may be constructed on streets without curbs, but steps should be taken to prevent circumnavigation around the humps in these situations.

Adequate signing and marking of each road hump is essential to warn roadway users of the hump's presence and guide their subsequent movements.

Road humps should not be installed in street sections where transit vehicles must transition between the travel lane and curbside stop. To the extent possible, road humps should be located to ensure that transit vehicles traverse the hump perpendicularly.

A single hump acts as only a point speed control. To reduce speeds along an extended section of street, a series of humps are spaced at between 300 and 600 feet apart.

Figure 32: Technical drawing of a round-top road hump.

i w + r l + y i t t t t R' t t t t ? $


Slope 1 in 8

in terwing brick, on bedding Send

Figure 33: Technical drawing of a flat-top road hump,

One Hump - I-- 3 0 ~ - ~ 4 Single Shod Bbck

,- w.1ooo' Two Humps - 3 Single Moderate a I Length Blodr

Three Humps - k 1000'.1&04 - Single long I a €I Modts

250

Multiple Humps - Lenglhy . continuous segmenls and multi-block segments

At least ons hump per block. Fdlow spadng concepls above within each component block. Maximum and minimum separallon and 'first hump' criteria may be relaxed somewhat to conform lo particular slle condhbns.

Figure 34: Example hump spacing plans for various road configurations.


Road Bumps

Description: Road bumps (or "speed bumps") are abrupt raised areas in the pavement in a distance of one to two feet, and are generally designed to be traversed at 5 to 10 mph. They are typically used in parking lots as a speed control device. Road bumps are not appropriate for public roadways and are not recommended for use.

Road Humps

Description: A road hump (or "speed hump") is a raised area in the roadway pavement surface extending transversely across the roadway. Road humps are less abrupt than road bumps and can have rounded or flat tops. Flat-top humps incorporate angled ramps, and generally feel less abrupt, than round-top humps that are parabolically curved. Road humps normally have a maximum height of three to four inches and a travel length of approximately twelve feet, though these dimensions may vary. As part of the Neighborhood Traffic Management Plan, the City of Atlanta currently has in place a speed hump installation program. Under the criteria of this program, no hump treatments are to be installed on roads classified as collectors.

. 1 Spwd Bump

Figure 31: Road bumps vs. Road humps

Advantages:

Vehicle speeds decrease at individual humps, and between humps in a series without increasing accident rates.

Humps can achieve desired results on vehicle operations without imposing unacceptable safety risks, since design and placement guidelines have evolved from extensive engineering, testing and research.

Accidents generally remain stable or decrease; speed humps have not been found to pose a safety hazard when properly designed and installed.

A rocking motion is created that results in most vehicles slowing to 15 miles per hour or less at each hump and to 25 to 30 mph between properly spaced humps in a system.

Speed and traffic volume reductions attributable to humps tend to remain constant over time.

The majority of residents along a street where road humps are installed typically support their continued use.

A visual impression that the street is not intended for speeding or cut-through traffic is created. , .

Humps represent a largely self-enforcing method of slowing traffic.


Disadvantages

Potential slowing of emergency and service vehicles. Road humps have been used to deter trucks and other large vehicles from using particular streets.

- Potential hazard for bicyclists

Increased vehicle noise

Potential diversion of traffic to other streets, especially if the street is being used as a shortcut or to handle overflow traffic from congested collectors or arterials. Volume reductions are affected by the number and spacing of humps and availability of alternate routes.

On-going maintenance costs,

Inconvenience for residents.

Street maintenance functions may be affected.

May be considered unsightly. However, this effect may be mitigated by the construction of humps with colored andlor textured materials.


If mid-block pedestrian crossings exist or are planned, they can be coordinated with speed hump installation since vehicle speeds will be lowest at the hump and pedestrians can then cross without having to negotiate ramps or curbs between sidewalk and street.

The humps must be visible at night.

Humps may be constructed on streets without curbs, but steps should be taken to prevent circumnavigation around the humps in these situations.

Adequate signing and marking of each road hump is essential to warn roadway users of the hump's presence and guide their subsequent movements.

Road humps should not be installed in street sections where transit vehicles must transition between the travel lane and curbside stop. To the extent possible, road humps should be located to ensure that transit vehicles traverse the hump perpendicularly.

A single hump acts as only a point speed control. To reduce speeds along an extended section of street, a series of humps are spaced at between 300 and 600 feet apart.

Figure 32: Technical drawing of a round-top road hump.

o 0 .H In 1.75 2.p 2 w 3PO 3.31 3 ~6 3.75 389 397 A.M.- 4' Hump 0 056 1.07 1.53 1.94 221 2 0 7.6) 3 1 1 3.211 3.40 3.48 3.54'-3.5' s~.odhJ(ump 0 OM C.02 1.3, 1.67 1.98 2.25 1.48 2.67 2 d l 2.82 2-94 3.W- J ' w H u m p


Slope 1 in8 1 in 12

IenQlh 1 in 15 28 lo 41 tl.

I 1 I 1 II

\ 11 11 I 1

\ Inlerlocking b r i i on bedding sand

Figure 33: Technical drawing of a flat-top road hump.

p- w-5m 4 One Hump. Single Short Block

- XX)..loOo' Two Humps- 3 Sinole Moderale F4 €l

Threo Humps - k 1000.-16W -------+ Single long kl a €I -

Muniplo Humps . Lenglhy . conlinuous segmenls and mulli~blodc segmenls

Al least one hum^ per Mock. Fdlow soacing Concepls above wilhin each component blodi. ~ a x i m u m and miniinurn ioparalion and 'firs1 hump' crileria may be relaxed somewhat to conlorn lo particular sile condiiiins.

Figure 34: Example hump spacing plans for various road configurations.

\ '.


'EE arn6!j u! u ~ o y s dwny peo~ ayl 6u!p!dap S ~ U ! M ~ J ~ la3!uy3al a y l : g ~ a ~ n 6 ! j

'PC a~n6! j u! u ~ o y s dwny peoJ aylGu!~!dap S ~ U ! M ~ . J ~ le3!uy3a) a y l :gg a ~ n 6 y

w a ~ e d ~301q pa~oloa y ) ! ~ papnrlsuo3 dwny peoJ dot-tell :E& arn6!j

.sasod~nd ~~&?u!&?JP 10) pappo~d s! lauueqs v 'do1 ~pqdsa pal lo^ pua sdwa~ pa~ed-yaolq 'pa~olw q 1 ! ~ dunq pear do1-1eu v :LC atn6!g

-sasod~nd a6eu!e~p Joj pap!~oJd s! lauuey3 y .dot lleydse palloJ pue sdwe~ pa~ed-y3olq 'pa~olo3 y l ! ~ dwny peo~ dol-ley y :LC arnlj!d

:o 'in

Figure 39: The technical drawing for the treatment shown in Figure 38.

Figure 40: A one-lane slow point incorporating speed cushions. speed cushions are similar to road humps but have a width less than the wheeltrack of a bus or truck but greater than that of an automobile.


Speed Tables

Description: Speed tables are similar to flat-top road humps. However, the device is elongated, and has a flat top which is long enough to accommodate both the front and rear wheels of a car to be on top of the table at once. Often the top of the speed table is constructed with colored and/or textured pavers to enhance the visual and tactile qualities of the structure. Thus, the device is generally 16 to 20 feet long (including the approaches). The devices are generally designed to be crossed at 20 to 25 mph at mid-block locations.

Since they have flat tops, they feel less abrupt than round-top road humps. Their curb-to-curb construction adds a measure of pedestrian safety not present in the design of flat-top road humps. Speed tables not long enough to accommodate both the front and rear wheels of a car on top of the table at once are often referred to as "raised crosswalks."

Advantages:

Reduced traffic speeds; similar to road humps. Increased safety for pedestrians and bicyclists due to slower speeds. No parking removal required.

Pedestrian and wheelchair users provided with a much easier street crossing at the same level as the sidewalk if raised crosswalk is constructed curb-to-curb.

More visible to drivers than flat crosswalks. No access restrictions for roadway users. No deviation from vehicle straight line path required. No impact on intersection operations.

Disadvantages:

Relatively high construction cost. May impact drainage. Potential, slight slowing impact on emergency services. Possible increase in traffic noise due to braking and acceleration of vehicles. Grade changes can create difficulty in crossing for'bicyclists; the visually impaired, and others.


Speed tables are applicable:

On roadways with vehicular speeds perceived as being incompatible with the adjacent residential land uses;

Where there is a significant number of pedestrian crossings;

In conjunction with other traffic calming devices, particularly entry treatments;

'On two-lane or less residential streets classified as either "local streets" or "neighborhood collector streets"; and

On roadways with 85Ih percentile speeds less than 45 mph.


Figure 41 : A speed table. Oftentimes, speed tables are placed near schools to serve as a pedestrian safety device.

Figure 42: A speed table with center median and pedestrian refuges installed as part of the design.

-. ,5" x 6 bullnose curb 1.5" hot rolled asphalt 4- wearing course

, - . . . ----I - -- -. -

level planed as required to achieve block and .. . . . . . . . . - Hand laid asphalt laying course.

Concrete ~ 7 . 5 ~ - . with Ronafix or equivelent

Figure 43: A technical drawing of the speed table shown in Figure 42.


Raised Intersections

Description: Raised intersections (sometimes referred to as "intersection humps") raise roadways at the intersection, forming a type of "plateau" across the intersection, with a ramp on each approach. The plateau is at curb level and can be enhanced (as with other treatments) through the use of distinctive surfacing such as pavement coloring, brickwork, or other textured pavers. In some cases, the distinction between roadway, sidewalk, and intersection crosswalk surfaces are blurred. If this is the case, physical obstructions such as bollards or planters should be considered, restricting the area to which motor vehicles have access.

Advantages:

Vehicles slowed in the most critical areas (at intersections); makes conflict avoidance easier. Visibility of intersection is increased.

Easier pedestrian crossings can be provided along a level path, assisting people in wheelchairs, the elderly, the visually impaired and others.

Disadvantages:

Increased difficulty for motorists wishing to turn at the intersection. May impact drainage. Discomfort or hazard to bicyclists if ramps are too steep or if surface materials are slippery.


Ramps should not exceed maximum gradient of 16%.

Distinctive surfacing helps reinforce the concept of a "calmed" area and thus plays a part in reducing vehicle speeds.

Distinctive surfacing materials should be skid resistant, particularly on inclines.

Ramps should be clearly marked to enable bicyclists to identify and anticipate them, particularly in conditions of poor visibility.

Care must be taken so the visually impaired have adequate cues to identify the roadway's location (e.g., tactile strips). Color contrasts will aid those who are partially sighted.

Figure 44: A raised, Clegged intersection.


Figure 45: A raised ''7'-intersection.

Joint Wdth at Shoulder Should Not Exceed 0.2'

.d.f

Existing Roadway

, . Plane O f Existing Roadway Surfacing

i To A Depth of 0.6" to 8 4 4" X'T' P C Block Paviors To Allow For Sand

I Class 22 5 120To Clause Laid on 1.4" to 2 Sharp Clean Bedding Course i 1801 Sand (Zone 2)

Galvanised Steel Angle 3.5' x 3.5" x 0 .2 Secured To Concrete Wth 0.4" Rawbolts Double Stretcher

Stretcher Course course At Shoulder I . r ,ilT,.?iT?i~m-I.. ;.. -- . . A' .. . ..:. -,' .. Herringbone Pattern

Bondina Detail

Crumpstall Traffic Calming Detail Of A Raised Intersection



-al!qouolne ue 40 ley1 ueyl JaleaJ6 lnq y3nJl JO snq e 40 y3leJjlaaynn ayl ueyl ssal q i p ! ~ e aney Inq sdwnq peal 01 Jel!u!s ale suo!ysn3 paads .suo!ysnDpaeds 6u!le~od~o3u! lu!od MOIS auel-auo :OP arn6!j

Traffic Circles

Description: Traffic Circles (sometimes referred to as roundabouts or rotaries) are raised circular islands (approximately four meters in diameter) that can be used as traffic calming devices at intersections, reducing vehicle speeds. Traffic at intersections where such treatments have been installed moves counter-clockwise around the central traffic island. These islands may be painted or domed, incorporate mountable elements, may be curbed and may include landscaping or other improvements.

Advantages:

Safety benefits have been associated with the implementation of traffic circles. Certain studies have found that traffic circles reduce accidents by 50 to 90 percent when compared to two-way, four-way stop signs and traffic signals by reducing the number of conflict points at intersections.

Effective in reducing motor vehicle speeds. Success, however, depends on the central island's being sufficiently visible and the approach lanes engineered to deflect vehicles, preventing overrun of the island. Over-runnable traffic circles on straight roads are less likely to produce the desired speed reduction.

Space for landscaping provided. Cheaper to maintain than traffic signals. Can create attractive, close range views along street; break up long view corridors. Effective at multi-leg intersections. Equal access to intersections for all users. Good environment for bicyclists can be provided, with proper design.

Disadvantages:

May be restrictive for larger vehicles if designed for too low a speed. By providing a mountable apron, this limitation can be minimized.

May require additional lighting.

If left turns by large vehicles are to be accommodated, additional right-of-way may be needed.

At locations where speed control islands or'other physical speed reduction measures are absent, bicyclists may suffer safety problems, particularly when turning right.

Despite noted safety benefits, and successful use in Seattle, Florida and Maryland, many jurisdictions (particularly in New Jersey) have removed traffic circles after installation due to safety concerns. Additionally, traffic circles can be a hazard to pedestrians when compared to conventional intersections. A discussion of the safety benefits of traffic circles is presented at the end of this section.


Traffic circles should preferably have sufficiently raised and highly visible centers to ensure that motorists use them, rather than over-running.

Clear signing is essential.

Complementary speed reduction measures, such as road humps, on the approach to traffic circles can improve safety.


The design of traffic circles must ensure that bicyclists are not squeezed by other vehicles negotiating the treatment. Yet where possible, adequate deflection must be incorporated on each approach to enforce appropriate entry speeds for motor vehicles.

Figure 47: A four-legged traffic circle scheme.

Figure 48: A traffic circle scheme at a "T"-intersection.


Both the'designs shown above incorporate "splitter islands." These are raised triangular concrete median islands centered on each approach of the traffic circle, separating entering and exiting traffic, and designed to deflect entering traffic. They are designed to prevent hazardous, wrong-way turning movements.

These islands represent important safety design elements and should be provided as a manner of routine, wherever feasible. Without splitter islands, left-turning motorists have a tendency to short-cut the turn and avoid driving around the outside of the central island. The islands should, preferably, be raised and landscaped. If this is not possible, painted markings should be provided. It has been suggested that the absence of splitter islands at traffic circles is the cause of their removal, in some cases, as more accidents at the intersection result with traffic circle installation.

DRAFT

DRAFT

Figure 49: A four-legged traffic circle scheme. Splitter islands are not included.


TYPICAL SECTION

CURB DETAIL

NOTES:

I. ALL MANHOLE AND WAFER VALVE COLLARS LOCATED WITHIN THE TRAFFIC CIRCLE SUALL BE RAISED TO THE WRREePONMNo OWDE OF THE PLANT MULCH MATERIAL.

2. FILL MATERIAL TO 8E MTERMINED BY ENOINEER

Figure 50: Technical drawing of a traffic circle center island.

(NO SCALE) I DET. NO.

CIRCLE

SECTION


Safety Benefits of Traffic Circles

Traffic circles have a reputation for being safer than conventional, four-legged intersections. A 1989 survey of accidents at intersections where traffic circles were installed versus conventional intersections found:

Traffic circles are most commonly used on streets with speed limits of 30 mph or less.

Traffic circles were found to have a far lower overallaccident rate than that of signalized intersections with equivalent speed limits.

In crashes only involving bicycles, the study showed that four-legged intersections with traffic circles installed have about the same accident rate (accidents per million vehicles entering the intersection) as do conventional, four-legged intersections.

The following comparative accident rates of four-leg, 30 mph intersections were also derived from the study:

Signalized Intersections

2.65 accidentslintersection/year 34 accidents1100 million vehicles 20% resulted in seriouslfatal injury

Traffic Circles

0.83 accidentslintersectionlyea 20 accidents1100 million vehicles 19% resulted in seriouslfatal injury.

In Seattle, a study of traffic accidents at 14 problem intersections found that the total number of collisions dropped from 51.6 to 22 after the installation of the circle. Accidents within a one-block radius also decreased from 101 to 33.

In another Seattle study of traffic circle intersections, fifteen intersections were studied for the same period of time before and after the construction of a circle. There was an average reduction from 1.94 to 0.18 collisions per year per location. Total collisions dropped from 33 to three per year. The decrease in collision rates is believed to be due to increased reaction time because of a reduction in motor vehicle speeds.

While traffic circles may be found to create safer intersections for vehicles, the same is not true for pedestrian safety. There are two reasons why traffic circles pose a hazard for pedestrians:

Constant vehicle movements can make it difficult for a pedestrian to find an adequate gap to cross.

Pedestrians unfamiliar with operations at traffic circles may not properly assess the flow of traffic at such intersections, resulting in an incident andlor injury,

Drivers unfamiliar with operations at traffic circles may not be ready or looking for pedestrian activity as they would at a conventional intersection.


Traffic Diverters

Traffic diverters are physical barriers installed at intersections that restrict motor vehicle movements in selected directions. The diverters may be designed to prevent right- or left-hand turns, to block straight-ahead travel and force turns to the right or left or create a "T" intersection. In all cases, paths, cut-throughs or other provision should be made to allow bicyclists and pedestrians access across the closure.

Turning Movement Diverters

Description: This type of diverter is designed to prevent cut-through traffic at the intersection of a neighborhood street with a major street or collector. It prevents straight-through movements and allows right-turns only into and out of the neighborhood.

Advantages:

Effective at discouraging cut-through traffic. Relatively low-cost. Creates sense of neighborhood entry and identity.

Disadvantages:

May restrict access to some neighborhood residents.

Figure 51 : Turning movement,diverters


Diagonal Road Closure/Diversion

Description: Straight-through traffic movements are prohibited. Motorists are diverted in one direction only.

Advantages:

Through traffic eliminated. Area for landscaping provided. Conflicts reduced. Pedestrian safety increased.

Can include a bicycle pathway connection.

Disadvantages:

Will inconvenience residents in gaining access to their properties. May inhibit access by emergency vehicles unless street names are changed. Will move through traffic to other streets if not back to the arterial.

Figure 53: A diagonal diverter.


Residential Neighborhood Gateway Treatments

Description: Residential neighborhood gateway treatments convert undistinguished entrances of residential areas into well-defined "gateways," which alert the driver that they are entering a special place. Gateways can be implemented by means of an entry structure or signing, in conjunction with other aesthetic features to emphasize the residential neighborhood. Other traffic calming devices (such as raised intersections or traffic circles) may be also used with gateway treatments, where appropriate, in order to achieve desired results.

Advantages:

Typically, motorists frustrated by congestion on major arterial and collector roadways will seek shortcuts. By providing high-quality gateway features at the entrance to a residential neighborhood, some bypass traffic may be diverted. In addition, gateways may improve the identity of a neighborhood, generating more community involvement to preserve the neighborhood.

Disadvantages:

If excess property is not available to install the sign at the entry, the corner property owner may be burdened with the sign, requiring histher concurrence (this concurrence cannot be expected). The community must maintain the gateway.

Guidelines for Use:

Gateways are installed at natural entry points to a residential neighborhood, especially where the neighborhood boundary changes in character (i.e., from a rural to commercial area to a residential area). The design of the gateway should reflect the character of the residential neighborhood. Gateway treatments tend to be ineffective unless they incorporate some form of physical narrowing, chicane, or vertical design elements.

Figure 54: A one-lane slow point, with appropriate priority traffic-flow and gateway signage, can serve as a gateway treatment.


.-. ---Rear of Ramp Sign

-" . .. ,3" Post

Cylindrical Bollard .r 1 Existing

-3" High

! 5 _Footway - 9 10" Road Hump Subway 1 Cycle 3' 4 Path 1. Footway Existing -, 1 d . w - -

- - ' " ? Y ~ ~ , - J I T ~ , ~ _ . - . . ~ : . Y . T '. I=-;- -- 7 f I : ' .-. Curbline to be Lowered

Curbline to be ~ohered ' White Line 9 . . Approx Location of Existing Stormwater

Drain

CROSS SECTION RAMP OUTSIDE NO. 10 CHURCH ROAD

Figure 55: A technical drawing depicting the gateway treatment shown in Figure 54.

MATFIELD Please drive

carefully through the village

Figure 56: Gateway treatments often incorporate signs like this that alert drivers to the fact that they are entering a neighborhood.

, .


Roadway Closures

Three types of roadway closures are described: Full roadway closures, partial roadway closures, and open roadway closures.

In many Georgia jurisdictions, including the City of Atlanta, it is a standard policy that road closures are not be implemented if they are detrimental to the interest of the public at large, and are to benefit only the surrounding neighborhood.

Administrative procedures exist to permit road closures when it is determined that a section of the municipal street system has ceased to be used by the public. These procedures, however, cannot proceed until the Office of Traffic and Transportation has made a determination that the road closure serves the public interest.

Full Roadway Closures

Description: Full street closures, generally on residential streets, can prohibit through traffic movement or prevent undesirable turns. Street closures may be appropriate where large volumes of through traffic or "short-cut" maneuvers create unsafe conditions in a residential environment.

Advantages:

Through traffic eliminated Speed of the remaining vehicles reduced. Safety for all other street users improved.

Disadvantages:

Emergency vehicle access may be restricted unless bollards, crash gates or other access ~rovision is made.

Street closures must be considered in an areawide context or traffic problems may simply shift to another nearby street.

Street closures are effective in achieving their stated objective, but can prove unpopular with residents where access is made more difficult.

If bicycle exemption is not provided, the closures may force bicyclists onto busier, less suitable alternative routes.

Where bicycle exemption is provided, the usefulness, the usefulness of cycle- gaps is much reduced if they are poorly designed and/or liable to obstruction by parked vehicles.


Where proposals are likely to lead to a reduction in access, prior consultation with residents at early stages of planning and design is especially important to minimize opposition.

The benefits of exempting bicyclists should be carefully considered in all cases.


Bicycle gaps should be designed to minimize the risk of obstruction by parked vehicles. Painting a bicycle symbol and other directional markings on the road in front of the bicycle gap has proved effective.

The use of bollards can reduce the parking obstruction. When used, bollards should be lighted or reflectorized to be visible at night.

The design of bicycle gaps should permit good visibility of adjacent roads.

Signing should acknowledge the continued route as a through one for bicyclists. ., , .

Clearly defined parking can reduce the problem of parked cars blocking the closure and bicycle gap.

Police and fire departments should be consulted early in the design process to determine emergency access requirements. Often, removable bollards, crash gates, card- or key-operated gates can satisfy these requirements, combined with parking restrictions. A 20-foot wide clear path is needed for emergency access.

Tree planting, benches and colored and/or textured paving can enhance appearance.

Street closures are recommended only after full consideration of all expected turning and reversing movements, including those of refuse trucks, fire trucks and other large vehicles.

Figure 57: A full roadway closure. Installed bollards allow free access for bicycles and pedestrians. They can be removed for entry by vehicles (under special circumstances).

They can also be used in pilot projects to test the acceptability of closures.


Bollard Detail (Not to scale)

reflective dim (both sides) re- Black and white pin1 detail

amCrete

[Nola:. some bdlerds will have to be below 3' 3" high above the g r w d due lo 'he slbpe dl he road (lo k&p a

Brook Street. Reaent Street, m s i s l f i wiphl)l

J-alkner Street. Conduit Street, Temporary Road Closures

Brook Street

3" Diameter Whrds

I. Exad localbn of ~ k r d s , kerbs lo be advised on sle]

(Not to scale)


Partial Roadway Closures

Description: Access to or from a street is prohibited at one end with a "no-entry" sign and barrier (a special type of curb extension called a semi-diverter) restricting traffic in one direction. The street remains two-way but access from the closed end is permitted only for bicyclists and pedestrians. (Also known as .one-way or half roadway closures.

Advantages:

o Discourages short-cutting through the neighborhood by restricting travel in one direction andlor limited turning movements.

Allows two-way traffic along the remainder of the street.


Disadvantages:

Emergency vehicles somewhat affected as they have to drive around partial closure with care.


Bicycle and pedestrian exemptions should be provided as a general rule, designed to minimize the likelihood of obstruction by parked vehicles.

All signing should acknowledge the continued existence of the route as a .. ... . . . . . . , through one for bicyc1,ists and pedestrians.

HALF ROADWAY CLOSURE

Figure 59: A partial roadway closure.

Open Roadway Closures

Description: Open roadway closures resemble full roadway closures, where the street character is significantly changed so it appears to be closed. However, the roadway is accessible to emergency and sanitary services.

Advantages:

Through traffic largely eliminated Large area for landscaping provided.. A very effective method of changing the initial impression of the street.


qJn3 dola pue dues a)amuo3 . '

*salqqaA asn4a.I pue A3ua6~awa o) Aluo palue.16 s! ssa33v .a~nsop r(a~peoJ uado uv :og arn6!d

Table 1 : Summary 01 Trafflc Calmlng Treatment Characteristics.

Full Roadway Closures1 59 1 Local I NIA I N/A I Yes I Serious I Yes I No I Yes I Yes 1 Yes 1 50-80 1 N/A I NIA I Varies I FUA I NIA I N/A I NIA Partial Roadway Closuresj 61 1 Local I NIA I N/A I Yes I Serious I Yes I No I Yes I Yes I Yes 1 7-10 1 NIA I NIA I Varies I NIA I NIA I N/A I NIA openRoadwayClosuresl 621 ~ocal I NIA I N/A I Yes I Serious I Yes I No I Yes I Yes I Yes 1 30-50 1 NIA I N/A I Varies I NIA I NIA 1 N/A I NIA

'--Condition Guidelines are meant for illustrative ~umosesonlv. Conditions *' -- A s~eed condition of either moderate or serious must also be resent

r

Dlverters

Turning Movement Divetlers

Diagonal Divetlen

and procdures such as those described on p.59 must be satisfied in order for a roadway to be taken out of service in the City of Atlanta

City of Atlanta Traffic Calmlng Device lmplementatlon Guidebook

Traffic Calming Device Procedural/Administrative/Regulatory Techniques

TumlEntry Prohibitions

Neighborhood Speed Watch Program

Radar Trailer

8

2 g

LIMITING TRAFFIC CONDITIONS

(if volume condition is deemed only moderate) for device to be wa;ranted.

X 5 2 - c S

LIMITING ROADWAY CONDITIONS MITIGATION ASSESSMENT IMPACT ASSESSMENT

12

13

14

54

56

a e .- E 0) .- ln

ln u

d a

a u

$

4.000 VPD or less

4,000 VPD or less

9

- - 3 8 0

.- 6 a - -

z c 8 $ s a 2"

& p t

B 5 5 - e

Local

Local. Collector

AT;or Physical Techniques - Horizontal Deflection Devices

N/A

NIA

WA '

NIA

Local

Local

Moderate"' Serious

Serious Moderate",

5

E >. z P Le


Striplng

Medians

Narrowlng Treatments Uslng Curb Extensions

One-lane Slow Points

Two-lane Slow Points

Curb Bulb-Outs

Neckdowns

Weaving Treatments

.

Collector

C~~~lor

Local

Local, Collector

Local

c',zor

Local, Collector

GElor

Local

&zor Local'

Collector

,$Tior

No

Yes

e

z B K

V )

- E - & a

16

18

21

22

27

28

30

NIA

NIA

Possible

NIA

Possible

Possible

No Possible. if

supplemented with

enforcement Possible. if

supplemented with

enforcement

NIA

NIA

5-10

15-25

6

C - .- P P

>

N/A

Moderate. Serious

Serious

Yes

Possible

Yes

Yes

Yes

Yes

Yes

Possible

Yes

Yes

Yes

Serpentine

Physical Techniques - Vertical Deflection Devices

Rumble Strips

Road Humps

SpeedTables

Raised Intersections

Traffic Circles

N/A

NIA

No

Yes

Yes

No

No

32

35

39

45

47

49

5% Trucks or less

5% Trucks or less

Yes

Yes

cu ii? 5 ii z 3 o - 3 8 u = - u g 5 4 0

NO

No

NO

Moderate, Serious

Mg:::

Moderate, Seriws

MSz2: Moderate' Serious

Moderate' Serious

Moderate' Serious

Moderate, Serious

Serious

Moderate' Serious

Moderate, Serious

Yes

Yes

Possible

Possible

Yes

Yes

Yes

NO

No

Possible

Yes

Yes

NO

30 or less

30 or less

Yes

Yes

m - d

s C m - - '2 u n t 4

4

NO

Yes

No

No

No

No

No

NO

No

No

No

NO

NO

No

Possible

Yes

Yes

No

Yes

Yes

Possible

No

Yes

Yes

Possible

No

Yes

Yes

NO

No

NO

Yes

NO

NO

Serious

NIA

NIA

No

No

Yes

Possible

Possible

Possible

Possible

Possible

No

Possbile

Possible

No

Possbile

No

No

Slight

sight

Slight

Slight

Slight

Slight

NO

Yes

Yes

Yes

yes

Moderate, Serious

NIA

Serious

NIA

NIA

NIA

NIA

NIA

NIA

N/A

N/A

N/A

NIA

0.6

10-50

10-15

Yes

NO

NO

No

No

NO

N/A

NIA

NIA

Beneficial if bicycle lanesare striped

Possible

Yes

Yes

Yes

Yes

Yes

No

Yes

Slight

Slight

Yes

yes

NIA

N/A

5% Trucks or less

or less lo%

5%TNcks0r less

l5:Eks

150/0Trucks or less

15% or less

NIA

5% Trucks less or

10% Trucks or less

lo%Truck or less

5% less

10-20

7-10

7-10

5-15

10-30

5-15

15-30

1-3

1-1.5

10-15

30-100

5-45

NIA

NIA

NIA

NIA

NIA

N/A

N/A

NIA

Visible fc

32rr

35 or less

35 or higher

30 Or less

NIA

N/A

N/A

Variable

NIA

NIA

35 or IU

35 or less

35 or less

35 or less

35 or less

35orless

25 or less

30 Or less

350r less

40 or less

VPD Or greater

10,000 VPD or less

3.000 VPD or less

NIA

NIA

N/A

NIA

N/A

NlA

0.6% W ~ a x i m u r NO installation on fc

51000 Or wNes wlradii < z r r less

7'000 less

7'000 VPD Or 0-6% less

NIA

No installation on wwes wlradii < wv

No installation on WNeS wlradii < 600'

NIA

NIA if jnstalled continuously over crest

WNBS

0-60h

10,000 VPD or less

7000 VPD or (collector),

less (local) 10,000 VPD

or less (collector),

7000VPDor less (local)

or less

4.000 VPD or less

5,000 VPD or less

7B000VPD0r less

10,000 VPD or less

(collector), 7000 VPD or less (local)

26' or greater

Varies

30' Or less

0-6%

0.;6%

I

N/A

&80h

0-81

0.6%

0.646

I

Minimum 24'

Minimum 24'

NIA

40' or less

40' or less

40'or less

40' or less

Conformily with

for Horizontal AASHTO Standards

Cu~ature

Conformity wilh AASHTO Standards

for Horizontal Curvature

. NIA

NIA

N/A

N/A

NO installation on fc

wlradii < 300' or more

NO installation on fc

wlradii < 300' or

NIA

NIA

more

NIA

Visible fc 300' or more

References

Pedestrian and Bicyclist Safety and Accommodation, Participant Workbook for NHI Course No. 38061, Publication No. FHWA-HI-96-028, May, 1996, pp. 69-135.

Guidelines for the Design and Application of Speed Humps, Prepared by ITE Traffic Engineering Council Speed Humps Task Force TENCdTF-01, Douglas W. Wiersig, Chair, 1997.

Nashville Neighborhood Traffic Management Pilot Program, Nashville Department of Public Works, May, 1998.

Neighborhood Traffic Calming Program for the City of Sunnyvale (CA) Final Report, Hank Mohle & Associates, November, 1996.

Neighborhood Traffic Management and Calming Program, City of San Buenaventura (CA) Department of Community Services Engineering Division, June, 1997.

Alameda County Neighborhood Traffic Calming Program, Alameda County Public Works Agency, January, 1997.

City of Portland (ME) Traffic Calming Policy Guidelines, DeLuca-Hoffman Associates, Inc., April, 1997.

City of Columbia (SC) Neighborhood Traffic Management Program, Wilbur Smith Associates, August, 1991.

Neighborhood Traffic Management Program Technical Manual, Wilbur Smith Associates for the City of Atlanta Department of Public Works 1 Bureau of Traffic and Transportation, April, 1980.

Neighborhood Traffic Management Program Manual, Wilbur Smith Associates for the City of Atlanta Department of Public Works 1 Bureau of Traffic and Transportation, April, 1980.

Traffic Calming in Practice, County Surveyors Society, Department of Transport, Association of Metropolitan District Engineers, Association of London Borough Engineers and Surveyors, Association of Chief Technical Officers, November, 1994.

The City of Portland's Neighborhood Speed Watch Program Evaluation, City of Portland, Oregon Office of Transportation, December, 1991.

City of Atlanta TraHc Calming Device implementation Guidebook

wilbur - atlanta, ga | home

Documents