urban street reliability evaluation using the highway capacity

James A. BonnesonKittelson & Associates, Inc.

July 2012

Urban Street Reliability EvaluationUsing the Highway Capacity Manual

OverviewOverview

• SHRP 2 Research Project L08 Overview• Evaluation Framework• Illustrative Analysis Capabilities

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Project L08 OverviewProject L08 Overview

• SHRP 2 Project L08• “Incorporation of Travel Time Reliability into the Highway

Capacity Manual”

• Objectives

– Determine how non-recurrent congestion impacts can be incorporated into HCM procedures

– Develop methodologies to predict travel time reliability on freeway facilities and urban streets

– Prepare a guide with that is suitable for potential inclusion in a future update of the HCM 2010

• Project schedule

– Ends March 2013

BackgroundBackground

• Terms– Scenario – a unique combination of volume and traffic control

conditions for one analysis period (e.g., 15-min, or 1 hour)

– Study period – one or more consecutive scenarios during a day (e.g., 3-hour period from 3:30 pm to 6:30 pm)

– Reliability reporting period – days evaluated (e.g., all week days for one year)

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Reliability Performance MeasuresReliability Performance Measures

• Basis of Reliability Performance Measures– Travel time distribution for reliability reporting period

• Goal– Quantify reliability of estimate travel time

• Basic Distribution Measures– Distribution statistics (e.g., standard deviation)

– Percentile-based measures (e.g., 95th percentile travel time)

• Normalized Measures– Buffer time: 95th % travel time divided by average travel time

– Planning time index: 95th % travel time divided by free-flow time

• Other Measures– On-time measures: percent trips completed by specified travel time

– Failure measures: percent trips not completed by specified travel time

Reliability Performance MeasuresReliability Performance Measures

Reliability Performance MeasuresReliability Performance Measures

• Buffer Time– 95th % travel time divided by average travel time

Travel time, s

Probability

00

LOS B LOS D

Travel time, s

Probability

00

LOS B LOS D

"Reliable" "Reliable"

"Unreliable" "Unreliable"

Reliability Performance MeasuresReliability Performance Measures

• Planning Time Index– 95th % travel time divided by free-flow time

Travel time, s

Probability

00

LOS B LOS D

Travel time, s

Probability

00

LOS B LOS D

"Reliable"

"Moderate Reliability"

"Unreliable"

"Unreliable"

Free-Flow Travel Time

Free-Flow Travel Time

FrameworkFramework

• Development Goals for Urban Streets Reliability Evaluation– Quantify the effect of non-recurring congestion sources

• Weather• Demand variation• Incidents• Work zones• Special events

– Minimize the amount of required input data

– Assemble a set of nationally-representative default values

– Use 2010 HCM Urban Streets methodology to compute travel time

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FrameworkFramework

• Work Flow– Start with the input data used to evaluate an urban street facility

using the 2010 HCM Urban Streets methodology• Enter the data in the urban streets engine and save it to a file• If desired, enter and save data for each work zone or special event

– Read the file and use it as a basis for scenario generation• Work day-by-day, analysis-period-by-analysis-period in chronologic

order through the year...– Predict weather events– Predict incident events– Adjust speed and saturation flow rate based on events– Adjust demand volumes using hourly, weekly, monthly factors– Save one revised file for each analysis period

– Submit each revised file to the urban streets engine

– Collect performance measures and compute reliability statistics

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Manual

Software

FrameworkFramework

• Flow Chart

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FrameworkFramework

• Input Data– Nearest city– Functional class– Analysis period duration (0.25 hr or 1.0 hr)– Study period duration (e.g., 7:00 am, extend for 3 hours)– Reliability reporting period (e.g., 1/1/2011, extend for 365 days)– Days of week considered (Su, M, Tu, W, Th, F, Sa)– Crash frequency by

• Segment• Intersection

– If work zone or special event present• Operating period (e.g., 4/1/2011, extend for 30 days)• Crash frequency adjustment factors

FrameworkFramework

• Work Zones and Special Events– Each is dealt with as a unique case for a unique time period

• Identify volume, geometry, and signal timing for each case– Include specific changes due to work zone or special event

» Lane closures» Alternative lane assignments» Special signal timing

• Create one urban streets engine input file for each case• Establish operating period (e.g., 4/1/2011, extend for 30 days)• Determine crash frequency adjustment factors

– Traffic demand changes• Not predicted• If analyst can estimate demand shifts, they can be reflected in

volumes entered in the input file

Urban Streets Reliability EngineUrban Streets Reliability Engine

• Welcome

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Scenario GenerationScenario Generation

• Set Up

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Scenario GenerationScenario Generation

• Set Up

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Scenario GenerationScenario Generation

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Performance SummaryPerformance Summary

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Performance SummaryPerformance Summary

• Performance Measures– By Direction

• EB/NB• WB/SB

– By System Component• Facility• Segment

– By Performance Measure• Travel time• Travel speed• Stop rate• Running time• Through delay

• Examples– EB direction

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Performance SummaryPerformance Summary

• Facility Travel Time (s) – PTI = 2.9

• Note– Maximum travel time

• 800 s

– Two crashes at same time but different intersections

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Summary StatisticsScenario evaluation interval: 1 Average: 120.38 5th percentile: 91.29Base free-flow speed, mi/h: 40.78 Standard deviation: 38.34 10th percentile: 92.45Base free-flow travel time, s: 60.20 Skewness: 7.72 80th percentile: 139.79

Median: 109.73 85th percentile: 143.76Number of obs.: 3120 95th percentile: 172.59

Planning Time

Performance SummaryPerformance Summary

Summary StatisticsScenario evaluation interval: 1 Average: 21.52 5th percentile: 14.22Base free-flow speed, mi/h: 40.78 Standard deviation: 4.29 10th percentile: 16.06Base free-flow travel time, s: 60.20 Skewness: -0.58 80th percentile: 25.91

Median: 22.37 85th percentile: 26.25Number of obs.: 3120 95th percentile: 26.89

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ABCDEF• Facility Travel

Speed(mi/h) • Note

– 10 percent of analysis periods have LOS E or F

Urban Streets Reliability MethodologyUrban Streets Reliability Methodology

• Framework– Overview of next three parts

• Scenario Generation• Facility Evaluation• Performance Summary• Illustrative Analysis Capabilities

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Illustrative Analysis CapabilitiesIllustrative Analysis Capabilities

• Alternatives Analysis– Compare base condition to alternative condition

• Analysis Scenarios– Work zones and special events

• Alternative start dates and durations• Alternative lane closures and signal timing strategies

– Weather• Examine operational effects of strategies that reduce weather-

related crashes or crash severity (i.e., snow removal, resurfacing)

– Incidents• Examine operational effects of strategies that reduce incident

duration• Evaluate benefit of providing shoulder for stalled vehicle refuge

– Design or Operation• Evaluate alternative signal timing plans• Evaluate intersection lane allocations or segment geometry

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ClosureClosure

• Questions or Comments?