hcm2000

Highway Capacity Manual 2000

A 4-Hour Introduction to HCM2000…

Part II: ConceptsPart II: Concepts

Part I - IntroductionPart II - ConceptsPart III – MethodologiesPart IV - Corridor and Area-Wide AnalysesPart V - Simulation and Other Models

Part II ChaptersPart II Chapters

n 7: Traffic Flow Parameters (13)n 8: Traffic Characteristics (32)n 9: Analytical Procedures Overview (12)n 10: Urban Street Concepts (51)n 11: Pedestrian and Bicycle Concepts (21)n 12: Highway Concepts (20)n 13: Freeway Concepts (30)n 14: Transit Concepts (33)

Part II Purpose and ContentPart II Purpose and Content

n To educate HCM users on LOS concepts and use• Facility-type concepts• Discussion of typical capacity parameters• Review of precision and accuracy of variables• Suggested default values• Sample service volume tables• Quick-estimation method for signalized

intersections (Chapter 10)

n To educate HCM users on LOS concepts and use• Facility-type concepts• Discussion of typical capacity parameters• Review of precision and accuracy of variables• Suggested default values• Sample service volume tables• Quick-estimation method for signalized

intersections (Chapter 10)

7: Traffic Flow Parameters7: Traffic Flow Parameters

n Uninterrupted Flow• Volume and flow-rate• Speed• Density• Headway and spacing• Relationships among

basic parameters

n Uninterrupted Flow• Volume and flow-rate• Speed• Density• Headway and spacing• Relationships among

basic parameters

n Interrupted Flow• Signal Control• Stop- or Yield-Controlled

Intersections• Speed• Delay• Saturation Flow Rate

and Lost Time• Queuing

n Interrupted Flow• Signal Control• Stop- or Yield-Controlled

Intersections• Speed• Delay• Saturation Flow Rate

and Lost Time• Queuing

7: Traffic Flow Parameters7: Traffic Flow Parameters

n Vehicle and Human Factors• Vehicles• Drivers• Pedestrians• Bicycles• Bus/LRT

8: Traffic Characteristics8: Traffic Characteristics

n Demand and Volume• Temporal variation• Analysis hour• Spatial distributions

– Directional– Lane

n Demand and Volume• Temporal variation• Analysis hour• Spatial distributions

– Directional– Lane

n Measured and Observed Values• Volume/Flow Rate• Speed• Headway• Saturation flow• Bus flow• Passenger flow

n Precision and Accuracy• Statistical accuracy of many methods not

known• Validation of current procedures generally not

statistically adequate• Stochastic properties of traffic should be

considered in judging appropriate degrees of complexity and sensitivity

n Precision and Accuracy• Statistical accuracy of many methods not

known• Validation of current procedures generally not

statistically adequate• Stochastic properties of traffic should be

considered in judging appropriate degrees of complexity and sensitivity

9: Analytical Procedures Overview9: Analytical Procedures Overview

HCM2000 StructureHCM2000 Structure

n Hourly and daily volume equivalencies• PHF• K-factor• D-factor

n Use and development of local defaultsn Use and development of service volume

tables

n Hourly and daily volume equivalencies• PHF• K-factor• D-factor

n Use and development of local defaultsn Use and development of service volume

tables

9: Analytical Procedures Overview9: Analytical Procedures Overview

n Urban Streets• Flow characteristics• Levels of service• Required input data and estimated values• Service volume table

10: Urban Street Concepts10: Urban Street Concepts

Example Service Volume TableExample Service Volume Table

n Signalized Intersections• Characteristics• Capacity and LOS• Required input data and

estimated values• Service volume table

n Signalized Intersections• Characteristics• Capacity and LOS• Required input data and

estimated values• Service volume table

Required Signal DataRequired Signal Data

Intersection Control TypeIntersection Control Type

Example Service Volume Table:Signalized Intersection

n Unsignalized Intersections• TWSC, AWSC, and roundabouts

– Characteristics– Capacity– Performance measures– Service volume tables

n Unsignalized Intersections• TWSC, AWSC, and roundabouts

– Characteristics– Capacity– Performance measures– Service volume tables

Example Service Volume Table:TWSC Intersection

Quick Estimation Method:Signalized Intersections

n Determines critical v/c, signal timing, and delay• Consists of six steps:

– 1) assemble input data– 2) determine left-turn treatment– 3) compute lane volumes– 4) estimate signal timing plan– 5) calculate critical v/c– 6) calculate average delay

n Determines critical v/c, signal timing, and delay• Consists of six steps:

– 1) assemble input data– 2) determine left-turn treatment– 3) compute lane volumes– 4) estimate signal timing plan– 5) calculate critical v/c– 6) calculate average delay

Quick Estimation Method:Signalized Intersections

n Input Data Requirements (some may be estimated):• Volumes• Lanes• Adjusted saturation flow rate• Left-turn treatment• Cycle length (min and max)• Lost time• Green time• Coordination (yes or no)• PHF• Parking (yes or no)• Area type (CBD or not)

n Terminology and principlesn Characteristicsn Performance measuresn Required input data and estimated valuesn Service volume tables

11: Pedestrian and Bicycle Concepts11: Pedestrian and Bicycle Concepts

Example Service Volume Table:Pedestrian Sidewalk

LOS Criteria for Uninterrupted Bicycle Facilities

12: Highway Concepts12: Highway Concepts

n Multilane highways• Capacity• Free-flow speed• Parametric relationships• Factors affecting free-flow speed• Factors affecting flow rate• LOS• Required input data and estimated values• Service volume table

Speed-Flow Relationships onMultilane Highways

Example Service Volume Table:Multilane Highway

12: Highway Concepts12: Highway Concepts

n Two-Lane Highways• Classification• Basic relationships• Passing lanes• LOS• Required input data and estimated values• Service volume table

Two-Lane Highways:Basic RelationshipsTwo-Lane Highways:Basic Relationships

Example Service Volume Table:Class I Two-Lane Highway

13: Freeway Concepts13: Freeway Concepts

n Freeway facilities• Basic freeway segments• Freeway weaving• Ramps and ramp junctions• Freeway facilities

n Concepts covered:• Fundamental characteristics• Important parameters• Service volume table

n Freeway facilities• Basic freeway segments• Freeway weaving• Ramps and ramp junctions• Freeway facilities

n Concepts covered:• Fundamental characteristics• Important parameters• Service volume table

Basic Freeway SegmentSpeed-Flow RelationshipsBasic Freeway Segment

Speed-Flow Relationships

Freeway Facility SegmentsFreeway Facility Segments

Freeway Facilities:Traffic Management Strategies

n Traffic management processn Freeway management strategies

• Capacity-management strategies• Demand-management strategies

n Performance measures

n Traffic management processn Freeway management strategies

• Capacity-management strategies• Demand-management strategies

n Performance measures

14: Transit Concepts14: Transit Concepts

n Introduction and definitionsn Transit facilities discussed:

• Bus– Loading areas– Stops– Busways– Exclusive arterial bus lanes– Mixed-traffic lanes

• Light rail• Street car

n Introduction and definitionsn Transit facilities discussed:

• Bus– Loading areas– Stops– Busways– Exclusive arterial bus lanes– Mixed-traffic lanes

• Light rail• Street car

14: Transit Concepts14: Transit Concepts

n Presented discussions:• Basic concepts• General capacity ranges• Priority treatments• Quality-of-service concepts

– Definitions – Performance measures– Quality-of-service factors– Quality-of-service framework

n Presented discussions:• Basic concepts• General capacity ranges• Priority treatments• Quality-of-service concepts

– Definitions – Performance measures– Quality-of-service factors– Quality-of-service framework

Relationship Between Person and Vehicle Capacity: Buses

Part III: MethodologiesPart III: Methodologies

Part III ChaptersPart III Chapters

15: Urban Streets (30)16: Signalized Intersections (174)17: Unsignalized Intersections (118)18: Pedestrians (34)19: Bicycles (26)20: Two-Lane Highways (52)21: Multilane Highways (32)22: Freeway Facilities (64)23: Basic Freeway Segments (32)24: Freeway Weaving (40)25: Ramps and Ramp Junctions (42)26: Interchange Ramp Terminals (18)27: Transit (46)

15: Urban Streets15: Urban Streets

n Changes since 1997 update:• Most major changes were incorporated into

the 1997 update– Intersection delay estimation procedures

• Chapter title has changed:– Arterial Streets Urban Streets

n Changes since 1997 update:• Most major changes were incorporated into

the 1997 update– Intersection delay estimation procedures

• Chapter title has changed:– Arterial Streets Urban Streets

15: Urban Streets15: Urban Streets

n Procedure assesses the mobility function of an arterial• Access function is not analyzed, but recognized as an

important considerationn Limitations of the Procedure:

• On-street parking effects• Driveway density• Lane additions/lane drops• Mid-block grades• Mid-block capacity constraints• Mid-block medians/TWLT lane• Turning movements greater than 20% of total volume• Upstream queue effects• Cross-street congestion

n Procedure assesses the mobility function of an arterial• Access function is not analyzed, but recognized as an

important considerationn Limitations of the Procedure:

• On-street parking effects• Driveway density• Lane additions/lane drops• Mid-block grades• Mid-block capacity constraints• Mid-block medians/TWLT lane• Turning movements greater than 20% of total volume• Upstream queue effects• Cross-street congestion

Urban Street MethodologyUrban Street Methodology

Methodology ChangeMethodology Change

No longer uses “analysis section”…just segments

Sensitivity of Results to Input Variables

Class I Urban StreetClass I Urban Street

Future PlansFuture Plans

n Enhancements• Running time sensitivity to flow rate• Improve sensitivity to filtering and metering

n Next Generation• Include evaluation of access impacts• Provide multimodal LOS

n Enhancements• Running time sensitivity to flow rate• Improve sensitivity to filtering and metering

n Next Generation• Include evaluation of access impacts• Provide multimodal LOS

Operational methodologyOperational methodology

The basic method remains essentially unchanged from 1997 updateThe basic method remains essentially unchanged from 1997 update

1. Input module

• Geometric conditions • Traffic conditions • Signalization conditions

2. Volume adjustment

• Peak-hour factor • Lane groups • Lane group volumes

4. Capacity analysis

• Lane group capacities • Lane group v/c ratios • Aggregate results

5. Level of service

• Lane group delays • Aggregate delays • Determine LOS

3. Saturation flow rate

• Ideal flow rate • Adjustments

1997 Changes to Chapter 91997 Changes to Chapter 9

n Improved Procedure for Actuated Signals

n Improved Delay Equation to Account for:

• Oversaturated Conditions

• Coordinated Operation

n Convert Primary MOE to Control Delay

n Account for Lane Utilization Effects on Saturation Flow Rates

n Change in Approach to Lost Time

n Fix Minor Problems with Permitted Left Turn Model

n Provide Better Guidance for CBD Factor

n Improved Procedure for Actuated Signals

n Improved Delay Equation to Account for:

• Oversaturated Conditions

• Coordinated Operation

n Convert Primary MOE to Control Delay

n Account for Lane Utilization Effects on Saturation Flow Rates

n Change in Approach to Lost Time

n Fix Minor Problems with Permitted Left Turn Model

n Provide Better Guidance for CBD Factor

Actuated SignalsActuated Signals

n Improved Procedure for Actuated Signals • Timing plans estimated using actual controller data and

signal design characteristics• Timing plan development is iterative (requires

computer)• Substantial improvements in delay and capacity

estimates for actuated control• Useful to evaluate optimum controller settings

n New Appendix II to estimate average splits• considers effects of initial, extension, maximum,

detector size, detector setback, etc.

n Improved Procedure for Actuated Signals • Timing plans estimated using actual controller data and

signal design characteristics• Timing plan development is iterative (requires

computer)• Substantial improvements in delay and capacity

estimates for actuated control• Useful to evaluate optimum controller settings

n New Appendix II to estimate average splits• considers effects of initial, extension, maximum,

detector size, detector setback, etc.

Improved Delay EquationImproved Delay Equation

n Improved Delay Equation• Delay equation to add third term (d3) accounting for

oversaturation• Accounts for varying length of congestion• Refinements for actuated control• Refinements to account for coordinated operation and

effects of upstream signals• Guidance to users on how to collect data in

oversaturated conditions• Multiple time periods• Arrivals vs departures

n Improved Delay Equation• Delay equation to add third term (d3) accounting for

oversaturation• Accounts for varying length of congestion• Refinements for actuated control• Refinements to account for coordinated operation and

effects of upstream signals• Guidance to users on how to collect data in

oversaturated conditions• Multiple time periods• Arrivals vs departures

The General Delay ModelThe General Delay Model

dd d++=

average total delay, in seconds/vehicled =d =

uniform vehicle delay component, adjusted for progression quality and for type of signal control(pretimed vs actuated) in seconds/vehicle

residual queue delay component to account for oversaturation queues that may have existed priorto the analysis period

random and oversaturation (incremental) delaycomponent, adjusted for the duration of the peakperiod, the type of signal control, and for upstreamtraffic signal effects, in seconds/vehicle

Where:

Oversaturated Time PeriodsOversaturated Time Periods

Analysis of Multiple Time Periods

1 2 3 4

Time Period

r)Analysis of Multiple Time Periods

1 2 3 4

Time Period

Capacity

Delay Model ComponentsDelay Model Components

LOS Based on Control DelayLOS Based on Control Delay

n Convert Primary MOE to Control Delay• Current HCM procedure estimates Stopped delay by

computing total delay and dividing by 1.3• Remove the 1.3 adjustment• Modify LOS thresholds upward

n Convert Primary MOE to Control Delay• Current HCM procedure estimates Stopped delay by

computing total delay and dividing by 1.3• Remove the 1.3 adjustment• Modify LOS thresholds upward

Subject toChange

1994 1997ABCDEF

< 5< 15< 25< 40< 60> 60

< 6.5< 19.5< 32.5< 52.0< 78.0> 78.0

Impact of Using Control DelayImpact of Using Control Delay

n New LOS Thresholds• 1.3 higher than before, rounded up

n New Survey Technique (Appendix III)• time in queue survey, with adjustments

n Consistent with Chapters 10 & 11 and Most Computer Models

Lane UtilizationLane Utilization

n Adjust for Lane Utilization Effects• Current HCM allows use of lane utilization

factor to adjust Volumes• Proposed change will not adjust volumes but

rather adjust saturation flow rates to reflect lane utilization effects (no fictitious vehicles)

• More accurate representation result in better estimate of average delay

• Saturation flow rate is better for other models (like TRANSYT and PASSER)

n Adjust for Lane Utilization Effects• Current HCM allows use of lane utilization

factor to adjust Volumes• Proposed change will not adjust volumes but

rather adjust saturation flow rates to reflect lane utilization effects (no fictitious vehicles)

• More accurate representation result in better estimate of average delay

• Saturation flow rate is better for other models (like TRANSYT and PASSER)

Computation of saturation flow rateComputation of saturation flow rate

Adjustment factors:

N = lanesf = lane widthf = heavy vehiclesf = grade

f = parkingf = localbusesf = area typef = right turnsf = left turns

s = s N f f f f f f f f f0 w HV g p bb a LU RT LT

] = lane utilizationflu

Lost TimeLost Time

n clarifications (e.g., Y includes all-red)n new variable

• e, extension of effective green into yellown calculate lost time, not input directly

• tL = l1+l2 (as before)

• l2 = Y-e (new calculation)

• g = G+Y-tL (as before)

n new defaults

Relationship between actual greenRelationship between actual greenand effective greenand effective green

r = R + t (effective red time)l

g = G + Y - t (effective green time)l

t ~ Y + ARl

CBD FactorsCBD Factors

n Guidance for CBD Factors• Better description of intent of CBD factor

– "Dense Business District"– Narrow sidewalks– Frequent parking– Small radius turns– High bus / taxi activity– High pedestrian volumes

• Should only be used in areas where geometric design and/or other factors (pedestrian, bus activity) significantly increase vehicle headways

n Guidance for CBD Factors• Better description of intent of CBD factor

– "Dense Business District"– Narrow sidewalks– Frequent parking– Small radius turns– High bus / taxi activity– High pedestrian volumes

• Should only be used in areas where geometric design and/or other factors (pedestrian, bus activity) significantly increase vehicle headways

HCM 2000 ChangesHCM 2000 Changes

n Re-organized and re-writtenn New queue modeln New ped-bike adjustmentsn New protected-permitted shared LT modeln Other minor changes

New Queue ModelNew Queue Model

n Back of queuen Accounts for coordinationn Accounts for actuationn Allows over-saturationn Allows initial queue & multi-periodn Predicts various percentile values

Permitted Left Turn ChangesPermitted Left Turn Changes

n Fix Minor Problems with Permitted Left Turn Model• Estimate of proportion of left turns in the left

lane on multi-lane approach• Adjustments to equation dealing with

boundary conditions (no or very low flow conditions)

n Fix Minor Problems with Permitted Left Turn Model• Estimate of proportion of left turns in the left

lane on multi-lane approach• Adjustments to equation dealing with

boundary conditions (no or very low flow conditions)

Unsignalized IntersectionsUnsignalized Intersections

n Most changes were incorporated into the 1997 update.• Two way stop controlled• All way stop controlled• Roundabouts

Two-way stop procedure includesTwo-way stop procedure includes

n Revised critical gap parametersn Revised methods for queue length estimatesn Revised control delay estimates

Analysis MethodologyAnalysis MethodologyUnsignalized IntersectionsUnsignalized Intersections

SummarizeDemandVolumes

SummarizePhysical

AdjustDemandVolumes

DevelopCritical GapAdjustments

ComputePotentialCapacity

DetermineImpedanceAdjustment

Factor

Evaluate 2-Stage

Gap Acceptance

EvaluateFlared Approach

Effect

ComputeMovementCapacity

EvaluateUpstream

Signal Effects

DetermineLOS

ComputeConflicting

DetermineProbability of

Queue-Free State

1994 HCM capacity equation1994 HCM capacity equation

ttC = 3600 eC = 3600 e

-Vt-Vt36003600

00(( ))

where:where:

V = conflicting volume (vph)V = conflicting volume (vph)

t = follow-up time (sec)t = follow-up time (sec)

t = critical gap (sec)t = critical gap (sec)

t = t - (t /2)t = t - (t /2)

00 cc ff

1997 HCM capacity equation1997 HCM capacity equation

c,yc,y

WhereWhere

VVccp,xp,x

= follow up time (sec)= follow up time (sec)

= critical gap (sec)= critical gap (sec)

= conflicting volume (vph)= conflicting volume (vph)= potential capacity for movement x (pcph)= potential capacity for movement x (pcph)

1 - e1 - e

eeC = VC = Vp,xp,x c,yc,y

36003600VV ttc,yc,y cc

36003600VV ttc,yc,y ff

Capacity for gap acceptance method

Field Capacity, veh/h

ModelCapacityVeh/h

100080060040020000

Critical Gaps and Follow-up TimesCritical Gaps and Follow-up Timesfor TWSC Intersectionsfor TWSC Intersections

wherewhere

ttc,adjc,adj c,basec,basett

3,LT3,LTttGGc,gc,gtt

c,Tc,TttHVHVPP++ ++ -- --==

= 0.7 sec for movement 7 or 10= 0.7 sec for movement 7 or 10

= Percent grade/100= Percent grade/100

= 0.1 for movements 9, 12; = 0.1 for movements 9, 12; 0.2 for movements 7, 8, 10, and 110.2 for movements 7, 8, 10, and 11

= 1.0 sec for movements 7, 8, 10, and 11= 1.0 sec for movements 7, 8, 10, and 11

= 1.0 sec for 2-lane road; 2.0 sec for 4-lane road= 1.0 sec for 2-lane road; 2.0 sec for 4-lane road

= Percent heavy vehicles in minor movement= Percent heavy vehicles in minor movement

tt c,HVc,HV

c,HVc,HV

PPHVHV

tt c,Gc,G

tt c,Tc,T

tt 3,LT3,LT

Critical Gap Adjustment FactorsCritical Gap Adjustment Factors

Follow-up Time Adjustment FactorsFollow-up Time Adjustment Factors

wherewhere

ttf,adjf,adj HVHVf,HVf,HVf,basef,basett tt PP++==

= 0.9 sec for 2-lane road; 1.0 sec for 4-lane road= 0.9 sec for 2-lane road; 1.0 sec for 4-lane road

= Percent heavy vehicles in minor movement= Percent heavy vehicles in minor movement

ttf,HVf,HV

PPHVHV

95th percentile queue length estimates

0 0.5 1 1.5

) C T = 1000

Revised control delay estimatesRevised control delay estimates

n Uses a similar equation to other chapters n Allows for D/C ratios to be greater than 1.0n Allows for any length of analysisn Allows for the acceleration and deceleration

associated with control delay

n Uses a similar equation to other chapters n Allows for D/C ratios to be greater than 1.0n Allows for any length of analysisn Allows for the acceleration and deceleration

associated with control delay

Unsignalized Intersection Delay EquationUnsignalized Intersection Delay Equation

Where:Where:

DD22 dd

ss 900T900T450T450Th xh x

x - 1x - 1(( )) x - 1x - 1(( ))++ ++ ++==

s = service times = service time

T = analysis periodT = analysis period

x = degree of utilizationx = degree of utilization

h = departure headwayh = departure headway

LOS is based on control delayLOS is based on control delay

Level of Service

A < 10 secB > 10 and < 15 secC > 15 and < 25 secD > 25 and < 35 secE > 35 and < 50 secF > 50 sec

Average Control Delayto Minor Street Traffic

Two-way stop procedure evaluatesTwo-way stop procedure evaluates

n Pedestrian effectsn Flared minor street approachesn Upstream signal effectsn Two stage gap acceptance processesn Through Traffic impedance effects

1: 2, 3, 5, 6, 15, 162: 1, 4,

13, 149, 12

3: 8, 114: 7, 10

1: 2, 3, 5, 152: 4,

13,149

1112 10

Cross Intersection

Rank Rank

T-Junction

Traffic Stream PrioritiesTraffic Stream Priorities

Definition of conflicting volumesDefinition of conflicting volumes

SubjectMovementSubjectMovement

Major StreetLeft Turn

Minor StreetThroughMovement

Minor StreetLeft Turn

V + V + vV + V + v

2V + V + 0.5V + V2V + V + 0.5V + V

+ 2V + V /N + 0.5V + 0.5V + 0.5V +V+ 2V + V /N + 0.5V + 0.5V + 0.5V +V

2V + V + 0.5V + V2V + V + 0.5V + V

V /N + 0.5V + VV /N + 0.5V + V

Minor StreetLeft Turn

No. Conflicting Traffic Volumes V

Conflicting Traffic Volume

Part I (near side from left)of 2-state gap acceptance process

Part II (far side from right) of 2-state gap acceptance process

+ 2V + V + 0.5V + V+ 2V + V + 0.5V + V1

Pedestrian impedancePedestrian impedance

f = (V )(w/s)f = (V )(w/s)36003600

wherewhere

= pedestrian blockage factor= pedestrian blockage factor

= pedestrian walking speed (assumed = pedestrian walking speed (assumed at 4 ft/sec)at 4 ft/sec)

= pedestrian volume (peds/hr and/or = pedestrian volume (peds/hr and/or groups/hr)groups/hr)

= lane width (ft)= lane width (ft)

Pedestrians effectsPedestrians effects

1015202530354045

0 20 40 60 80 100

Pedestrians per hour

KACTUAL

CSHARED

CFLARED

CSEPARATE

QUEUE k

Effect of flared minor approachEffect of flared minor approach

Flared minor street approachesFlared minor street approaches

0 1 2 3Flare length (vehs)

Upstream signal parameters include

n The distance between intersectionsn Signal timingsn Travel speed on the arterialn Saturation flow rates

Effect of Upstream SignalsEffect of Upstream Signals

SIGNAL 2

SIGNAL 5

FLOWSPROBABILITY

"SPREAD RATIO" = t /t1

SIGNIFICANT IF D OR D < 1500 FT (500 m)(1/4 mile)

2 3 41

part II

part I

input line

m spaces for passenger cars

The two-stage gap acceptance processThe two-stage gap acceptance process

Two-stage gap acceptance processes

0 1 2 3

Median storage (vehs)

Shared lane delay to rank 1 movementsShared lane delay to rank 1 movements

d = rank 1; N > 1

; N = 1

dmajor left

V + Vi,1 i,2

Analysis MethodologyAnalysis MethodologyUnsignalized IntersectionsUnsignalized Intersections

SummarizeDemandVolumes

SummarizePhysical

AdjustDemandVolumes

DevelopCritical GapAdjustments

ComputePotentialCapacity

DetermineImpedanceAdjustment

Factor

Evaluate 2-Stage

Gap Acceptance

EvaluateFlared Approach

Effect

ComputeMovementCapacity

EvaluateUpstream

Signal Effects

DetermineLOS

ComputeConflicting

DetermineProbability of

Queue-Free State

The all-way stop procedureThe all-way stop procedure

n Based on the notion that the service time is a function of the conflict type

n The more difficult the conflict - the longer the service time

n Defines “degree-of-conflict” casesn The process is iterative

n Based on the notion that the service time is a function of the conflict type

n The more difficult the conflict - the longer the service time

n Defines “degree-of-conflict” casesn The process is iterative

Key Operating ConceptsKey Operating Concepts

AWSC intersections operate in eitherAWSC intersections operate in either2- or 4-phase patterns2- or 4-phase patterns

Vehicle headways depend onVehicle headways depend on

Degree of conflictDegree of conflict

Vehicle typeVehicle type

Turn maneuverTurn maneuver

Intersection geometryIntersection geometry

AWSC analysis computational procedureAWSC analysis computational procedure

Input Data

Saturation Headways

Departure Headwaysand Service Time

Capacity andLevel of Service

Operating states of AWSC intersectionsOperating states of AWSC intersections

Case 1 Case 2 Case 3

Case 4 Case 5

Richardson capacity modelRichardson capacity model

Intersection of one-way streetsIntersection of one-way streets

Intersection of two-way streetsIntersection of two-way streets

Generalized model for single lane sitesGeneralized model for single lane sites

Generalized model for multi-lane sitesGeneralized model for multi-lane sites

Departure headway Departure headway

n The mean departure headway is a function of probability of the “degree-of-conflict” case and the departure headway (or service time).

n The probabilities are themselves a function of the departure headways.

n The mean departure headway is a function of probability of the “degree-of-conflict” case and the departure headway (or service time).

n The probabilities are themselves a function of the departure headways.

Intersection of one-way streetsIntersection of one-way streets

Where:

s = service time with no vehicle on conflicting approach

= arrival rate

s = service time with vehicle on conflicting approach

s = mean service time for northbound approach

SubjectApproach

ConflictingApproachs =

s 1 - (s + s )1 1N 2

1 - (s + s )1 12

N W 22

Capacity and delayCapacity and delay

n The capacity is evaluated by increasing the traffic demand on the subject approach until the degree of utilization is equal to 1.0.

n The delay is evaluated using a non steady state equation similar to the one used in the TWSC section and in other chapters.

n The capacity is evaluated by increasing the traffic demand on the subject approach until the degree of utilization is equal to 1.0.

n The delay is evaluated using a non steady state equation similar to the one used in the TWSC section and in other chapters.

Emergence of Roundabouts in the U.S.A.Emergence of Roundabouts in the U.S.A.

n Interest first appeared in early 1990’sn Maryland and Florida produced first guidesn Most states now show an active interestn FHWA has released a national guide

Methods of evaluating roundaboutsMethods of evaluating roundabouts

AnalyticalAnalyticalCritical gap, follow-up timeCritical gap, follow-up timeSIDRA (Australian)SIDRA (Australian)

EmpiricalEmpiricalRegression function based on geometricRegression function based on geometricfeaturesfeaturesARCADY, RODEL (British)ARCADY, RODEL (British)

SimulationSimulationMicroscopic modeling of roundaboutsMicroscopic modeling of roundaboutsCORSIM, Integration, ParamicsCORSIM, Integration, Paramics

Injury accident reductionsInjury accident reductions

Britain 35%35%

36%36%

38%38%

55%55%

74%74%

75%75%

78%78%

51%51%

Denmark

Switzerland

The Netherlands

Norway

Australia

France

United StatesUnited States

Source: Maryland Department of Transportation; NCHRP synthesis

Roundabout procedureRoundabout procedure

n Based on a gap acceptance approachn Evaluated on limited US field experiencen Provides two estimates of capacity and offers

no advice on delays• FHWA Guide offers additional information on:

– Capacity estimation (single and double-lane)– Delay estimation

n Based on a gap acceptance approachn Evaluated on limited US field experiencen Provides two estimates of capacity and offers

no advice on delays• FHWA Guide offers additional information on:

– Capacity estimation (single and double-lane)– Delay estimation

Comparison with othersComparison with others

Australia (Troutbeck)

Suggestedrelationship(exponential)

Circulating Flow (veh/h)

Entrycapacity(veh/h)

12001000800600400200200

German

Comparison with othersComparison with others

EntryCapacity(veh/h)

12001000800600400200200

Australia(Troutbeck)

Suggestedlower-boundrelationship

Circulating Flow (veh/h)

German

Increased criticalgap parameters

Roundabout evaluationRoundabout evaluation

n Suggest that the upper-bound is more appropriate for most roundabouts.

n Use the lower bound estimate when the speeds are particularly low and if roundabouts are not common.

n Suggest that the upper-bound is more appropriate for most roundabouts.

n Use the lower bound estimate when the speeds are particularly low and if roundabouts are not common.

Single-Lane RoundaboutsSingle-Lane Roundabouts

0 400 800 1200 1600 2000 2400Circulatory Flow (veh/h)

Urban & Rural Single-Lane Roundabouts

Urban Compact Roundabouts

Entering and circulating flow = 1800 veh/h

Double-Lane RoundaboutsDouble-Lane Roundabouts

0 400 800 1200 1600 2000 2400 2800 3200 3600

Circulatory Flow (veh/h)

Capacity AdjustmentsCapacity Adjustments

n Short lanes (flared approaches)

n Pedestrians

n Short lanes (flared approaches)

n Pedestrians

Capacity adjustments: Short lanesCapacity adjustments: Short lanes

No. of vehicle spaces in short lane

Capacity factor (applied to double-lane approach capacity)

0 (single-lane approach) 0.500 1 0.707 2 0.794 4 0.871 6 0.906 8 0.926

10 0.939

n Short lanes are the additional partial lanes added when flaring a roundabout from one to two lanes

Capacity adjustment: Pedestrians at single-lane roundabout

0 100 200 300 400 500 600 700 800 900

100 ped/h

200 ped/h

300 ped/h

400 ped/h

circular flow rate qk [pcu/h]

Reduction factor M [-]

Capacity adjustment: Pedestrians at double-lane roundabout

0 200 400 600 800 1000 1200 1400

100 ped/h

200 ped/h300 ped/h

400 ped/h

Reduction factor M [-]

circular flow rate qk [pcu/h]

DelayDelay

n Control delay• Includes initial deceleration delay, queue

move-up time, stopped delay, and final acceleration delay

n Geometric delay• Delay experienced by a single vehicle with no

conflicting flows• Caused by geometric features

n Total delay = Control + Geometricn Typical measure used: control delay

n Control delay• Includes initial deceleration delay, queue

move-up time, stopped delay, and final acceleration delay

n Geometric delay• Delay experienced by a single vehicle with no

conflicting flows• Caused by geometric features

n Total delay = Control + Geometricn Typical measure used: control delay

DelayDelay

0 400 800 1200 1600 2000 2400

Entering flow (veh/h)

400 veh/h 800 veh/h 1200 veh/h 1600 veh/h 2000 veh/h 2400 veh/hCapacity

T=0.25 hT=0.25 h

400 1600

Queue EstimationQueue Estimation

n Average queue (50th percentile)• Equivalent to vehicle-hours of delay per hour

on an approach• Useful for comparing performance with other

intersection formsn Maximum queue (95th percentile)

• Used for design purposes• Most common queue parameter

n Average queue (50th percentile)• Equivalent to vehicle-hours of delay per hour

on an approach• Useful for comparing performance with other

intersection formsn Maximum queue (95th percentile)

• Used for design purposes• Most common queue parameter

50th Percentile (Average) Queue Estimation

Little’s rule:L = v * d / 3600

where:L = queue length, vehv = entry flow, veh/hd = average delay, s/veh

Little’s rule:L = v * d / 3600

where:L = queue length, vehv = entry flow, veh/hd = average delay, s/veh

95th Percentile Queue Estimation95th Percentile Queue Estimation

0 0.2 0.4 0.6 0.8 1.0 1.2 1.41

5678910

5060708090100

v/c Ratio [-]

Highway Capacity Committee’s web siteHighway Capacity Committee’s web site

HCM User’s web site (maintained by FHWA)HCM User’s web site (maintained by FHWA)

HCM Web SitesHCM Web Sites

http://traffic.ce.gatech.edu/hcqs

http://www.hcmweb.net

http://www-mctrans.ce.ufl.edu/info-cen/hcs/hcs.htm

HCS software siteHCS software site

+ = HCM2000

BOOKCD-ROM

.pdf files

Multimedia version

tutorials

examples

audio explanations

video clips

hypertext/search

software link

3rd party software

27: Transit Analysis27: Transit Analysis

n Chapter is summary of Transit Capacity and Quality of Service Manual.

n Capacity and LOS estimates are provided• Bus• LRT

n Chapter is summary of Transit Capacity and Quality of Service Manual.

n Capacity and LOS estimates are provided• Bus• LRT

Typical Busway Line-Haul Passenger Volumes

Average Bus Speed in a Freeway HOV Lane

Base Bus Running Time (min/mi)

Bus Running Time LossesBus Running Time Losses

Skip-Stop Speed Adjustment Factor

Bus Lane Volumes and SpeedsBus Lane Volumes and Speeds

Factors Influencing Transit Capacity and Speed

Transit LOS AnalysisTransit LOS Analysis

n Quality of service is computed at three different levels of aggregation:• Transit Stop• Transit Route• Transit System

Transit LOS AnalysisTransit LOS Analysis

n Six Quality of Service Criteria are identified at each level of aggregation.• Service Frequency• Hours of Transit Service• Passenger Load• Reliability• Service Coverage• Ratio of Transit to Auto Travel Times

Transit LOS AssessmentTransit LOS Assessment

n Service Frequencyn Service Frequency

n Hours of Servicen Hours of Service

n Passenger Loadn Passenger Load

n Bus Service Reliabilityn Bus Service Reliability

n Ratio of Auto to Bus Travel Tiimen Ratio of Auto to Bus Travel Tiime

Transit AnalysisTransit Analysis

n Additional performance measures can be computed• Bus & rail stop dwell time.• Bus & rail stop capacity• Mean bus speed

– freeway HOV lanes.–urban street bus lanes.–Mixed flow lanes

• Mean rail speed• Vehicle and person capacity of bus lanes.

n Additional performance measures can be computed• Bus & rail stop dwell time.• Bus & rail stop capacity• Mean bus speed

– freeway HOV lanes.–urban street bus lanes.–Mixed flow lanes

• Mean rail speed• Vehicle and person capacity of bus lanes.

Parts IV and V: Corridor and Area-Wide Analyses and Simulation

Part IV & V ChaptersPart IV & V Chapters

n 28: Assessment of Multiple Facilities (6)n 29: Corridor Analysis (33)n 30: Areawide Analysis (39)n 31: Simulation and Other Models (37)

Parts IV and V:Purpose and Content

n To provide guidance on the use and adaptation of HCM procedures for corridor and area-wide analyses

28: Assessment of Multiple Facilities28: Assessment of Multiple Facilities

n System analysis framework• Roadway structure (points, segments,

facilities, corridors, area-wide)• Facility types (arterial, freeway, rural

highway)

n System analysis framework• Roadway structure (points, segments,

facilities, corridors, area-wide)• Facility types (arterial, freeway, rural

highway)

Facility

Corridor

Areawide

Segment

n Six Measures of System Performance

• Quantity of congestion• Intensity of congestion• Duration of congestion• Extent of congestion• Variability• Accessibility

n System Performance Report Card• Modal LOS Report Card (A/C/A/D)

n Six Measures of System Performance

• Quantity of congestion• Intensity of congestion• Duration of congestion• Extent of congestion• Variability• Accessibility

n System Performance Report Card• Modal LOS Report Card (A/C/A/D)

28: Assessment of Multiple Facilities28: Assessment of Multiple Facilities

System Performance Evaluation:“Report Card” Approach

29: Corridor Analysis29: Corridor Analysis

n Guidance on the Application of Part III Chapters to Corridor Analysis

n Highway Corridor Methodology• Compute segment capacity• Adjust temporal demand for Bottlenecks• Compute free flow speed• Compute actual speed• Compute queue delay• Compute performance measures

n Transit/Highway Corridors

n Guidance on the Application of Part III Chapters to Corridor Analysis

n Highway Corridor Methodology• Compute segment capacity• Adjust temporal demand for Bottlenecks• Compute free flow speed• Compute actual speed• Compute queue delay• Compute performance measures

n Transit/Highway Corridors

30: Area-wide Analysis30: Area-wide Analysis

n Extension of the HCM to Regional Planning Models

n Highway Facilities Methodology• Determine free flow speed• Determine link capacity• Determine link speed• Determine performance measures

n Transit Facilities Methodologyn Example Problems

n Extension of the HCM to Regional Planning Models

n Highway Facilities Methodology• Determine free flow speed• Determine link capacity• Determine link speed• Determine performance measures

n Transit Facilities Methodologyn Example Problems

Determination of Link SpeedDetermination of Link Speed

31: Simulation and Other Models31: Simulation and Other Models

Typology of ModelsTypology of Models

n Strengths of simulation models• Treats variations in time and space• Considers interactions of queues

n Shortcomings of simulation models• Requires considerable input• Requires verification, calibration, and

validation• Can provide misleading results to users

who are not sufficiently familiar with the base assumptions and processes

n Strengths of simulation models• Treats variations in time and space• Considers interactions of queues

n Shortcomings of simulation models• Requires considerable input• Requires verification, calibration, and

validation• Can provide misleading results to users

who are not sufficiently familiar with the base assumptions and processes

n Simulation Model Descriptors• Stochastic vs. Deterministic Models• Event Based vs. Time Based Models• Micro, Meso, Macro Models• Static Flow vs. Time Varying Models• Descriptive vs. Optimization Models

n Examples

n Simulation Model Descriptors• Stochastic vs. Deterministic Models• Event Based vs. Time Based Models• Micro, Meso, Macro Models• Static Flow vs. Time Varying Models• Descriptive vs. Optimization Models

n Examples

n Selecting a Model• Determining Project Scope• Assessing HCM Methodologies• Selecting a Model

– Model Capabilities– Data Availability– Ease of Use– Past Performance– Validation/Calibration

n Selecting a Model• Determining Project Scope• Assessing HCM Methodologies• Selecting a Model

– Model Capabilities– Data Availability– Ease of Use– Past Performance– Validation/Calibration

Performance Measures for Uninterrupted Flow FacilitiesPerformance Measures for

Uninterrupted Flow Facilities

hcm2000

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