introduction - nysmpos.orgnysmpos.org/.../uploads/2017/04/training_signal-traffic-principles.pdf ·...

Introduction

Lorenzo Rotoli, P.E., PTOEVice President

Heath Lagoe, P.E.Sr. Traffic Engineer

Tim Faulkner, P.E.Sr. Transportation Manager

Signal Timing & Traffic Engineering Principles

Purpose: Provide a basic understanding of traffic engineering

Motorists’ perception:

Traffic problems –Anytime I don’t have a green light

Course Outline

• Types of Studies• Traffic Signal Phasing• Break #1• Vehicle Detection and Operating Modes• Traffic Signal Timing Parameters• Advanced Elements of Signal Timing• Break #2• Traffic Signal Operational Parameters• Sample Problems

References

• Federal Highway Administration• NYSDOT• Highway Capacity Manual• Manual of Uniform Traffic Control Devices• Institute of Transportation Engineers• Your local transportation agencies

Traffic Studies

Traffic is the foundation of most projects• Capacity & Safety

Traffic Engineering Studies

• Determine characteristics of roadway users• Monitor operations• Identify problem areas• Assist in developing remedial action

ITE’s Manual of Transportation Engineering Studies describes 18 types of studies

Traffic Volume Studies

Traffic Volume StudiesNumber of Vehicles or pedestrian passing a given point on a roadway at a specific time

• Class of vehicle• Travel direction• Turning movement• Lane of travel• Time period

Terminology

• Avg Annual Daily Traffic (AADT) o Vehicles per year/365

• Avg Daily Traffic (ADT)o 24 hour volume

• Avg Weekday Traffic (AWT)o 12:01 AM Monday – 12:00 midnight Friday

• Design Hourly Volume (DHV)o 1 hour volume (flow rate) – basis of design

Count Periods

• Peak period countso Typically 7 am-9 am and 4 pm-6 pm

• 24 hour counts• 72 hour counts• Weekend

o 6 pm Fri – 6 am Mon

• Unique events: Commercial, sports, school…

Example - Hourly volume data sheet

Example – Intersection TMC

Miscellaneous

• Avoid unusual count conditionso Poor weather, holidays, special events, etc

• Seasonal Adjustmentso Summer tourism

• Accidents – STOP COUNTING

Types of Volume Studies

• Turning Movement Counts (TMC)o Intersection design, capacity

analysis, signal phasing

• Directional counts

• Classification counts – car, trucks, buses, etc

• Pedestrian, Bicyclist, Occupancy, Cordon, etc

Speed Studies

Speed StudiesMeasures individual speeds of a sample of vehicles passing a point on a roadway

Purposes:• Speed trends• Establish speed limit & curve speeds• Establish no passing zones• Proper sign locations• Evaluate Intersection sight distance• Geometric design• Before and After studies• Crash analysis

Speed Study Locations & Factors

• Not where vehicles are changing speed

• Data collectors must not impact speed

• Factors that influence speedo Weather, heavy traffic, police presence

• Free-flowing vehicles (off peak hours)o 100 veh/lane min, rep speeds, not too many

trucks

Data Collection Techniques

• Machine recorders

• Floating car

• Video based (distance versus time)

• Radar

Curve Advisory Speed

• Ball Bank Indicator

Travel Time and Delay Studies

Evaluate the quality of traffic movement along a route and determine the locations, types, and extent of traffic delays

• Evaluate congestion• Signal timing studies• Before and After studies• Trends over time

Terminology

• Travel time – elapsed time of travel• Running time – time that vehicle is in motion• Travel speed – overall avg speed• Delay -

o Stoppedo Control deviceo Operational

Techniques

• Floating car travel time runso Stop watcho Laptopo GPS

• License plate (time & license # recording)

Intersection Delay Studies

Intersection Delay Studies

Determine control delay at signalized or stop controlled intersections

• Based on Highway Capacity methodology• Level of Service criteria

o How many vehicles are stoppedo How long are they stoppedo Control device delayo Queued vehicles

Little or No Delay

Minor, Short Delay

Average Delays

Long, Acceptable Delays

Long Delays

Long, Unacceptable Delays

Signal Warrant Study

A study to determine whether installation of a traffic control signal is justified at a particular location. Based on MUTCD warrants.

Warrant 1 - Eight-Hour Vehicular VolumeWarrant 2 - Four-Hour Vehicular VolumeWarrant 3 - Peak HourWarrant 4 - Pedestrian VolumeWarrant 5 - School CrossingWarrant 6 - Coordinated Signal SystemWarrant 7 - Crash ExperienceWarrant 8 - Roadway NetworkWarrant 9 - Intersection Near a Grade Crossing

Signal Warrants

• Satisfaction of one or more warrants does NOT mean a signal is required

• Signals can introduce more delay

• Signals can increase Rear End accidents

• Use engineering judgement

Gap Study

• Determines the time and space that a vehicle or pedestrian needs to merge/cross between two successive vehicles on the mainline road

Gap acceptance: A minor stream vehicle accepts an available gap to maneuver

Headway: The time interval between the arrivals of two successive vehicles. Headway differs from gap because it is measured from the front bumper of the front vehicle to the front bumper of the next vehicle

Origin and Destination (O-D) Studies

Determine existing travel patterns and trip choices

Identifies: • Pass through traffic• Specific routes• How they travel • When they travel

Origin and Destination (O-D) Studies

Data is collected: • Interviews• License plate surveys• Videos• Mail back surveys

Vehicle Queueing

• Document existing vehicles per lane• Calibrate traffic models• Determine auxiliary lane requirements

Safety Studies

• Determine high accident locations & mitigation• Improve roadway designs

Safety Studies

• Collect police motor vehicle accident reports (MVA’s)

• Typically 3 year period• Sort by Locations, Types and Severity• Create collision diagrams• Analyze to identify patterns• Develop mitigation

Safety Studies

Safety Studies

• Accident Rate calculated per Million Vehicles

• Compared to historical average accident rates for similar facility

Safety Studies

• Road segment is calculated as:

Where:R = Crash rate for the road segment expressed as crashes per 100 million vehicle-miles of travel (MVMT)C = Total number of crashes in the study periodN = Number of years of dataV = Number of vehicles per day (both directions)L = Length of the roadway segment in miles

:

Safety Studies

• Intersection rate is calculated as:

Where:R = Crash rate for the intersection expressed as accidents per million entering vehicles (MEV).C = Total number of intersection crashes in the study period.N = Number of years of data.V = Traffic volumes entering the intersection daily

Safety Studies

• Develop mitigation measures• Determine Benefit/Cost ratios

Traffic Signal Phasing

Traffic Signal Phasing• Signal phasing represents the method by which

a traffic signal accommodates the various users at an intersection in a safe and efficient manner.

• A phase is defined as a controller timing unit associated with the control of one or more movements

• An interval is a duration of time during which the signal indications do not change.

• A vehicle phase is one that is allocated to one or more vehicular movements.

• A pedestrian phase is one that is allocated to pedestrian traffic that may provide either concurrent or exclusive pedestrian movement.

• A traffic phase is one that has the green, change (yellow) and clearance (all red) intervals for a specified movement of traffic.

• A cycle is the total time to complete one sequence of signalization for all movements at an intersection.

Phasing & Movement Diagram For Two One-Way Streets

Typical Vehicular & Pedestrian Movements at a 4-Leg Intersection

Standard Ring & Barrier Diagram

• Permissive Only• Protected Only• Protected+Permissive• Split Phasing• Prohibited

Left Turn Display Options

• Requires left turning vehicles to yield to conflicting vehicle and pedestrian traffic.

• Served concurrently with adjacent through movement.

• Primarily used with light to moderate traffic and good sight distance.

• Most efficient operation for allocation of green time at an intersection.

• Efficiency is dependent upon the availability of gaps in opposing traffic.

• Can have adverse effect on safety.

Permissive Only Left Turn Phasing

Permissive Only Left Turn PhasingRing and Barrier Diagram

• Allows left turning vehicles to turn without conflict.

• Provides for efficient left turn movement operation, however added left turn phase may increase delay to other movements.

• Typically requires an exclusive left turn lane.

• This type of operation is recognized as the safest left turn operation.

Protected Only Left Turn Phasing

Protected Only Left Turn PhasingRing & Barrier Diagram

• Represents a combination of permissive and protected modes.

• Provides for efficient left turn movement operation often without significant increases in delay to other movements.

• This type of operation provides for relatively safe left turn operation provided there is adequate sight distance and there are gaps in traffic.

Protected + Permissive Left Turn Phasing

Protected + Permissive Left Turn PhasingRing and Barrier Diagram

• Represents an assignment of right-of-way to all movements on one approach followed by all movements on an opposing approach.

• Typically less efficient than other types of left turn phasing because of longer cycle lengths and/or reduced green times if there is a fixed cycle length.

Split Phasing

Split PhasingRing and Barrier Diagram

• Can be total prohibition of only during certain times of the day, such as peak hours when gaps are unavailable and operation of permitted phasing may be unsafe.

Prohibiting Left Turns

• Left Turn and Opposing Through Volumes• Number of Opposing Through Lanes• Cycle Length• Speed of Opposing Traffic• Sight Distance• Intersection Geometry• Crash History

Guidelines for Selecting Left Turn Phasing

• Lead – Lead Left Turn Phase Sequence• Lag – Lag Left Turn Phase Sequence• Lead – Lag Left Turn Phase Sequence

Left Turn Phase Sequence Options

• Most commonly used left turn phase sequence.• If single ring is used, then opposing left turn phases

terminate at same time. If an actuated dual ring structure is used then left turn phases can be of different length.

• Advantages are that drivers react quickly to leading green arrow indication and minimizes conflict between left turn and through movements on the same approach.

Lead – Lead Left Turn Phase Sequence

• Most commonly used in coordinated systems with closely spaced signals.

• Both left turn phases end at same time.• If single ring is used, then opposing left turn

phases also start at same time. • Offers operational benefits at “T” intersections,

intersections of a two-way street and a one-way street and at a pair of closely spaced interconnected intersection where left turns operate in protected+permissive mode.

Lag – Lag Left Turn Phase Sequence

• Generally used to accommodate through movement progression in coordinated systems.

• Offers operational benefits where there is inadequate space in the intersection to safely accommodate simultaneous left turn movements or at intersections where the leading left turn movement is not provided an exclusive lane or available storage is short.

Lead – Lag Left Turn Phase Sequence

• Typically served concurrently with the adjacent through movement at an intersection. Typical application puts pedestrians in conflict with right turning vehicles and left turning vehicles.

• Leading pedestrian interval• Lagging pedestrian interval• Exclusive pedestrian phase

Pedestrian Phasing

• Starts a few seconds before adjacent through movement phase.

• Allows pedestrians to establish presence in crosswalk and reduce conflicts with turning vehicles.

• Supports increased pedestrian safety by providing them with increased visibility with intersection.

• Applicable to intersections where there are significant pedestrian/vehicle conflicts.

Leading Pedestrian Interval

• Starts several seconds after adjacent through movement phase.

• Allows a waiting right turn queue to clear before pedestrian indication is given.

• Applicable to intersections where there is a high right turn volume and either an exclusive right turn lane or the intersection of two one-way roadways.

Lagging Pedestrian Interval

• Dedicates an additional signal phase for the exclusive use of all pedestrians.

• Pedestrians can cross in any direction and even may be allowed to cross diagonally.

• Safest form of pedestrian phasing.• Comes with a penalty of reduced vehicular capacity and

longer cycle lengths which increases delay for all vehicles.• Has the chance of not being used correctly by

pedestrians.

Exclusive Pedestrian Interval

Vehicle Detection & Operating Modes

• Detection at an intersection informs the signal controller that a user desires service.

• Controller uses this information and the signal timing to determine the signal to display to the users.

• Traditional detector loops can be of different design depending on the type of detection.

• Newer technology includes wireless detection and video detection.

Vehicle Detection

• Objectives of Vehicle Detection• Types of Detection• Detector Operating Modes• Controller Memory Modes

Vehicle Detection

• Identify vehicle presence on a phase.• Extend the phase to serve queued vehicles and

that which is progressed from upstream traffic signals.

• Identify gaps in traffic where the phase may be ended to extend the green.

• Provide safe phase termination for high speed movements.

Detection Objectives

• Pulse Mode – detects the passage of a vehicle by motion only (point detection). Actuation starts with arrival of vehicle and ends with after pulse duration. Typically used when the detector is located upstream of the stop line

• Presence Mode – Used with long loop detection. Actuation starts with arrival of vehicle and ends when vehicle leaves detection zone.

Detector Operating Modes

• Refers to the controller’s ability to “remember” a detector actuation. One of two modes can be used: non-locking or locking.

• Non-locking – Actuation is not retained by the controller after the actuation is dropped by the detector.

• Locking – The actuation received by the controller is used to trigger a continuous call for service.

Controller Memory Modes

Traffic Signal Timing Parameters

Traffic Modeling

• Data collection• Existing system model

Traffic Modeling – Data collection• Turning movement counts• Intersection Inventory

• Geometry, detectors, signal timings, parking• Observations

Traffic Modeling – Existing system model

• Overview:• Process field data• Adjust & balance volumes• Create existing Synchro model• Calibration

Traffic Modeling – Existing system model• Calibration

Source: TRB

Traffic Signal Timing Parameters

• Types of Traffic Signal Operation• Phase Intervals and Basic Parameters• Actuated Timing Parameters• Detection Parameters

Types of Traffic Signal Operation

• Pre-timed• Semi-actuated• Actuated

Pre-timed Signal Operation

• Fixed duration intervals• Application:

• Central Business Districts• Work Zones

• Benefit:• Predictable operation• Low cost/maintenance• Can be coordinated

• Disadvantages• Non-flexible

Actuated Signal Operation

• Operation utilizing detection• Detector input and controller parameters

• Semi-actuated or Fully-actuated

Semi-Actuated Signal Operation• Detection only for minor movements

• Dwell in non-actuated phase• Application:

• Coordinated arterials• Roadways with light side street traffic

• Benefit:• Reduces mainline delay• Medium cost/maintenance• Can be coordinated

• Disadvantages• Delay due to poor parameters coded in

controller

Fully-Actuated Signal Operation• Detection for all movements• Application:

• Isolated intersections• Intersection of two arterials

• Benefit:• Responsive to changing traffic patterns• Efficient allocation of green time• Reduced delay

• Disadvantages• Higher installation/maintenance costs• Higher percentage of stops

Traffic Signal Operation Comparison

Source: FHWA Traffic Signal Timing Manual

Phase Intervals & Basic Parameters• Vehicular Green Interval• Vehicle Change & Clearance Intervals• Pedestrian Intervals


Vehicular Green Interval

• Time dedicated to serving vehicular traffic with a green light

• Minimum Green• Maximum Green

Minimum Green (Minimum Initial)• Reaction• Driver Expectancy• Queue• Pedestrian


Maximum Green• Conflicting demand• Limit delay to other movements


Vehicular Change and Clearance Intervals

• Safe transition between two conflicting phases• Change: Yellow interval

• Driver Perception-Reaction Time• Time to come to comfortable stop• Typically 3 to 6 seconds

• Clearance: All red interval• Time for vehicles to clear intersection• Typically should not exceed 6 seconds

Vehicular Change and Clearance Intervals• Resources:

• MUTCD• NCHRP 731: Guidelines for Timing Yellow &

All-Red Intervals• Equations:

Pedestrian Intervals

• Time dedicated to serving pedestrians• Walk• Pedestrian Clearance:

• Flashing Don’t Walk (FDW)• Don’t Walk

Walk

• Walking Person• Start of Green Interval• React & Enter Crosswalk• MUTCD: Minimum 7 seconds• Rest in Walk:

• Remains in walk as long as the traffic signal is green & there are no calls on conflicting street.

Pedestrian Clearance

• Flashing Hand with Countdown• Complete crossing • MUTCD:

• Time to far side of traveled way or median

• Walking speed: 3.5 ft/sec

Pedestrian Clearance

• Calculation

FDW = W / WS

Where:FDW = Flashing Don’t Walk time (seconds)W = Walking (Crossing) DistanceWS = Average Walking Speed (3.5 ft/sec)

Don’t Walk

• Solid Hand• Do not enter crosswalk• Onset of yellow

Pedestrian Intervals

Source: MUTCD

Actuated Timing Parameters

• Phase Recalls• Passage Time• Dual Entry• Gap Reduction


Phase Recalls• Controller coded call for specified phase • Minimum Recall• Maximum Recall

• Pre-timed operation desired• No vehicle detection• Gapping out not desired

• Pedestrian Recall• No pedestrian detection• High pedestrian demand

• Soft Recall• Similar to semi-actuated• Low volume mainline

Passage Time• Extends green interval up to maximum green• Gap or vehicle extension• Typically 1 to 4 seconds


Dual Entry

• Calls vehicle phases to occur concurrently even if only one phase receives a call

• Through movements

Gap Reduction• Reduces the passage time to a smaller value

• Time before reduction• Time to reduce• Minimum gap


Gap Reduction• Typical Values

• Time before reduction = Minimum Green• Time to reduce = Half the difference between Minimum

& Maximum Green


Detection Parameters• Call

• Actuates green interval• Extend

• Increases duration of the green actuation• Safe phase termination - high speed

approaches• Call & Extend

• Actuates green interval & increases duration of the green actuation

• Queue• Extends green interval until queue is served

Advanced Elements of Signal Timing

Advanced Elements of Signal Timing

• Traffic Signal Coordination• Signal Preemption• Signal Priority

Traffic Signal Coordination

Green

Red


Green

Red

Traffic Queue


• Traffic signal coordination is the synchronization of two or more intersections along a section of roadway

• TSM technique that is used to improve overallintersection operations usually quantified as reduction in overall intersection delay and maximizing arterial progression

Traffic Signal Coordination-Benefits/Outcomes

• Improve capacity of the existing street system by reducing delays and stops

• Provide smooth, continuous platoon progression • Reduce accidents• Reduce environmental footprint through

reduction in fuel consumption and exhaust emissions

• Minimal capital improvements• Cost-effective traffic management actions

Traffic Signal Coordination –Benefits/OutcomesNational average:

• 40:1 return on investment

Source: USDOT

Traffic Signal Coordination -Misconceptions

• Signal Coordination can improve the operations of any street.

• Signal Coordination is for close spaced signals

• ½ to ¾ mile spacing threshold

• Signal Coordination will not mitigate mid-block non-signal related issues


• If the signals on a corridor are coordinated then drivers will never need to stop at a red light.

• Signals must accommodate: • Pedestrian timings• Heavy demand on side streets• Left turn phases


• Signal Coordination will create excessive speeds.

• Signals are coordinated using the posted speed limit.

Traffic Signal CoordinationSignal Variables:

• Cycle length• Time required to cycle through all signal intervals

• Yield Point• Point where controller makes a decision to terminate

the coordinated phase• Splits

• Time allocated to each phase• Force-offs

• Points where non-coordinated phases must end

Traffic Signal CoordinationSignal Variables:


Traffic Signal Coordination - Signal Variables:• Offset

• Time relationship between coordinated phases at subsequent signals

• Reference point


Traffic Signal CoordinationCorridor Wide Variables:

• Volumes & direction distribution• Speed• Time of day• Special detection• Side street traffic – heavy turning volumes

Traffic Signal CoordinationPre-timed vs. Actuated:

• Pre-timed• Downtown closely spaced intersections - Grid• Fixed – Simpler but rigid• Pedestrian friendly

• Actuated• Arterials• Less rigid – more complex


Signal Timing Plan Sequence:• Start with calibrated Existing Conditions model• Calculate yellow/all red clearance times • Calculate ped crossing times• Cycle Length Evaluation• Optimization of splits & offsets

• Automated• Manual

• Interpretation of results

Traffic Signal Coordination – Signal Timing Plan


• Time-Space Diagram

Traffic Signal Coordination – Signal Timing Plan• Simulation Review

Traffic Signal Preemption

• The transfer of normal operation of a traffic control signal to a special control mode of operation

• Designed and operated to give the most important classes of vehicles the ROW through a signal

• Typically utilized by fire & other emergency vehicles

Traffic Signal Preemption• Preemption detection utilizes:

• Strobe light• Siren• Loops• Radio• Pushbuttons


Traffic Signal Priority (TSP)• An operational strategy that is applied to

reduce the delay for transit vehicles at traffic signals

• Communication between buses and signals to give priority to transit.

• Methods• Extending green interval• Truncating red interval

Traffic Signal Priority (TSP)


Traffic Signal Priority (TSP)

• Differences from Preemption• Preemption disrupts normal signal operations

• Phases may be skipped• Coordination interrupted

• TSP maintains normal signal operations • Priority request may not be granted • Does not interrupt coordination of traffic signals

Adaptive Traffic Signal Control

• On-demand signal operation• Adjusts signal timing parameters in real-time

to respond real-time traffic conditions• Critically linked to good detection systems

Adaptive Traffic Signal Control

• Useful for:• Traffic conditions fluctuate randomly on a day-to-

day basis• Traffic conditions change rapidly due to new or

changing developments in land use• Incidents, crashes, or other events resulting in

unexpected changes to traffic demand

Traffic SignalOperationalParameters

• Level of Service/Delay• Queue Length• Volume-to-Capacity (V/C)• Travel Time• Travel Speed• Density

Performance Measures

• Delay is the additional travel time experienced by a vehicle and can be divided into two parts, total delay and control delay.

• Total delay is the difference between actual travel time and theoretical travel time.

• Control delay is the portion of total delay that is attributable to the control device plus the time decelerating to a queue, waiting in queue, and accelerating from a queue.

Delay

• Level of service is a measure of how much control delay there is for an individual movement, approach or intersection and is represented by a letter grade.

• For signalized intersections, typically strive for LOS C, however LOS D is considered acceptable in urban areas.

Level of Service

Level of Service CriteriaSignalized Intersections

Level of Service CriteriaOther Modes

• Queue length is a measurement of the physical space vehicles will occupy while waiting to proceed through an intersection.

• Commonly used to assess the amount of storage needed for turn lanes and to determine whether vehicles will back from one intersection into an adjacent intersection.

• Average queue and 95th

percentile queue are the common measures of queue length.

Queue Length

• Measure of the actual volume to the actual capacity of a lane and identifies the degree of saturation.

• Movements or lane groups with a V/C or 0.85 or less are considered under saturated and typically have sufficient capacity and stable operations.

• For V/C ratios of 0.85 to 1.00, traffic flow becomes less stable due to variations in traffic flow.

• For V/C ratios greater than 1.00, queues will not clear every cycle and will extend into adjacent intersections.

Volume-to-Capacity Ratio (V/C)

• Identifies how well a series of signalized intersections fit together.

• Performance measures include stops, travel time and travel speed.

Arterial and Network Performance Measures

Arterial Level of Service

Sample Problems

Sample Problems: Hertel Avenue, Buffalo

Sample Problems: Church Street, Cortland

Questions?

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