Traffic Assignment and Feedback Research to Support Improved Travel Forecasting

328 Pages·2015·17.76 MB·English

Traffic Assignment and Feedback
Research to Support Improved Travel
Forecasting

Prepared for:
Federal Transit Administration
Office of Planning and Environment
Under Contract No. DTFT60-11-D-00009
Prepared by:
Caliper Corporation
Cover photos:
“Link and I-5 southbound from S 144th Street” by SounderBruce / CC BY 2.0
“Dallas_Exterior_2086” by Kinkisharyo / CC BY 2.0
“Future City” by Neil Kremer / CC BY 2.0
“Seattle Trolley Bus” by Oran Viriyinci / CC BY 2.0
“Phoenix Traffic Assignment” and “Intersection Simulation” courtesy of Caliper Corporation
Traffic Assignment and Feedback Research
to Support Improved Travel Forecasting

FINAL REPORT

Prepared for:

Federal Transit Administration
Office of Planning and Environment
Under Contract No. DTFT60-11-D-00009

Prepared by
Caliper Corporation
1172 Beacon St
Newton, MA 02461
www.caliper.com
July 31, 2015

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Planning Organizations that participated in the research.
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4. TITLE AND SUBTITLE 5a. CONTRACT NUMBER
DTFT60-11-D-00009
T raffic Assignment and Feedback Research to Support Improved Travel Forecasting 5b. GRANT NUMBER

5c. PROGRAM ELEMENT NUMBER

6. AUTHOR(S) 5d. PROJECT NUMBER

Howard Slavin, Jim Lam, and Kanchana Nanduri 5e. TASK NUMBER

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REPORT
C aliper Corporation
1172 Beacon St., Suite 300
Newton, MA 02461
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Analysis Division, TPE-22
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Washington, D.C. 20590

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1 3. SUPPLEMENTARY NOTES

14. ABSTRACT

This research investigated whether or not current traffic assignment and model feedback practices are sufficiently
accurate for calculating congested highway travel times and for quantifying the highway benefits of major transit
projects. Examination of U.S. MPO modeling practices indicated widespread deficiencies in implementation.
Empirical investigation of assignment and feedback convergence errors present in some of the better MPO models
indicated that with available methodological improvements and more extensive computation, existing methods
could produce plausible estimates of highway and transit project impacts. Comparisons between modeled and
measured congested travel times from commercial sources indicated that models tended to underestimate travel
speeds, and that use of speed data would be beneficial in model calibration and validation.

15. SUBJECT TERMS
Traffic assignment, user equilibrium, travel time measurement, demand model calibration and validation, speed feedback,
model convergence
16. SECURITY CLASSIFICATION OF: 17. LIMITATION 18. NUMBER 19a. NAME OF RESPONSIBLE
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Standard Form 298 (Rev. 8-

98)
Table of Contents
Chapter 1 Introduction and Executive Summary ............................... 1-1
Study Approach ........................................................................................................................1 -2
Inventory of MPO Modeling Practices ...................................................................................... 1-3
MPO traffic assignment practices ....................................................................................... 1-3
MPO feedback practices .................................................................................................... 1-3
Detailed Examination of Selected MPO models ....................................................................... 1-4
An Overview of the 5 MPO Models .......................................................................................... 1-4
Network geography and attributes ...................................................................................... 1-5
Volume-delay functions ...................................................................................................... 1-5
Assignment methods and convergence ............................................................................. 1-5
Traffic Assignment Investigations and Findings ....................................................................... 1-5
Validation of models with traffic counts .............................................................................. 1-6
Feedback Research and Findings ............................................................................................ 1-7
Project Impact Analysis ............................................................................................................1 -7
Congested Travel Times from MPO Models ............................................................................ 1-8
Summary Conclusions and Recommendations ........................................................................ 1-9
Recommendations for FTA guidance ............................................................................... 1-10
Research recommendations ............................................................................................. 1-11
Concluding remarks ..........................................................................................................1 -11
Chapter 2: Inventory of MPO Traffic Assignment Modeling
Practices ............................................................................................ 2-1
Introduction ...............................................................................................................................2 -1
Background on Equilibrium Traffic Assignment Models and Convergence .............................. 2-2
Current MPO Traffic Assignment Procedures ........................................................................ 2-13
Concluding Remarks ..............................................................................................................2 -15
Chapter 3 Current Practices in Computing Model Feedback ............ 3-1
Background on Feedback Convergence .................................................................................. 3-1
Feedback Methods in Use ........................................................................................................3 -5
Concluding Remarks ................................................................................................................3 -7
Chapter 4: Overview of the ARC, MAG, NCTCOG, PSRC, and
SANDAG Models ............................................................................... 4-1
Model Information Summary Tables ......................................................................................... 4-2
MPO Model Formulations .........................................................................................................4 -8
Trip purposes ......................................................................................................................4 -8
Travel modes ......................................................................................................................4 -9
Traffic Assignment Problem Characteristics ............................................................................. 4-9
Network size & software ..................................................................................................... 4-9
Geographic network representation ................................................................................. 4-10
Turn prohibitions and penalties ........................................................................................ 4-10
Centroid connectors .........................................................................................................4 -12
Area types ........................................................................................................................4 -16
AM trip characteristics ...................................................................................................... 4-20
Capacities .........................................................................................................................4 -25
PCEs for vehicle classes .................................................................................................. 4-26
Transit preloads ................................................................................................................4 -26
Assignment generalized cost impedance functions .......................................................... 4-26
Values of time ...................................................................................................................4 -26
Volume-delay functions .................................................................................................... 4-27
MPO Base Model Traffic Assignments ................................................................................... 4-34
Trip speeds .......................................................................................................................4 -35
Concluding Remarks ..............................................................................................................4 -39
Chapter 5 Traffic Assignment Models and Tests ................................ 5-1
Traffic Assignment Runs ..........................................................................................................5 -2
Volume-to-capacity ratios ................................................................................................... 5-4
Zero flow link analysis ........................................................................................................5 -7
Convergence Error Analysis ..................................................................................................... 5-9
Comparison of Assignment Volumes and Traffic Counts ....................................................... 5-14
ARC flows and counts ...................................................................................................... 5-15
MAG flows and counts ...................................................................................................... 5-17
NCTCOG flow versus count comparison .......................................................................... 5-20
PSRC flow versus count comparison ............................................................................... 5-23
SANDAG flow versus count comparisons ........................................................................ 5-24
Validation of multi-class assignments ............................................................................... 5-32
Other Traffic Assignment Investigations ................................................................................. 5-33
Analysis of operating costs in traffic assignment impedance ........................................... 5-33
PSRC trip rounding analysis ............................................................................................. 5-38
Conclusions ............................................................................................................................5 -41
Chapter 6 Feedback Methods and Convergence Tests ...................... 6-1
Overview of the 5 MPO Model Feedback Approaches ............................................................. 6-1
Closure metrics and tolerances .......................................................................................... 6-3
Initial speeds .......................................................................................................................6 -3
Bus speeds .........................................................................................................................6 -3
Appropriateness of feedback closure metrics ..................................................................... 6-4
Feedback Runs ........................................................................................................................6 -5
Feedback runs with the MAG model .................................................................................. 6-6
NCTCOG model feedback runs ........................................................................................ 6-12
Feedback in the PSRC model .......................................................................................... 6-20
Feedback runs with SANDAG activity-based model ......................................................... 6-20
Conclusions ............................................................................................................................6 -26
Chapter 7 Project Impact Analysis ....................................................... 7-1
Impact of a Roadway Project in Atlanta .................................................................................... 7-2
Impact of a Roadway Project in Phoenix .................................................................................. 7-7
MAG mode choice and assignment with highway project added ..................................... 7-11
MAG single loop run with highway project added ............................................................. 7-13
MAG full model run with highway project added............................................................... 7-16
Impact of a Transit Improvement Project in Phoenix .............................................................. 7-19
MAG mode choice and assignment with transit project added ......................................... 7-20
Transit project impacts assessed with a MAG full model run ........................................... 7-25
Impact of a Roadway Project in Dallas-Ft. Worth ................................................................... 7-31
NCTCOG AM highway assignment-only results with highway project added .................. 7-32
Added lanes assessed with the NCTCOG mode choice and assignment models ........... 7-34
Lane expansion evaluated with a full NCTCOG model run .............................................. 7-37
Impact of a Light Rail Extension in Dallas-Ft. Worth .............................................................. 7-41
Light rail extension impact with the NCTCOG mode choice and assignment models ...... 7-43
Light rail extension impact assessed with an NCTCOG full model run ............................ 7-47
Impact of a Roadway Project in the Puget Sound region ....................................................... 7-54
Impact of a widened arterial in the PSRC region .............................................................. 7-54
PSRC full model run with highway project added ............................................................. 7-60
Impact of a Roadway Project in San Diego ............................................................................ 7-63
Assignment-only analysis ................................................................................................. 7-64
Impacts assessed with a single model loop...................................................................... 7-68
SANDAG full model run with highway project added ....................................................... 7-70
Impact of a Transit Project in San Diego ................................................................................ 7-74
Transit project impacts with a SANDAG single loop model run ........................................ 7-75
Transit project impacts from a full SANDAG model run .................................................... 7-79
Conclusions ............................................................................................................................7 -85
Chapter 8 Congested Travel Time Analysis ........................................ 8-1
ARC Model Speed Analysis ..................................................................................................... 8-3
MAG Model Speed Analysis ..................................................................................................... 8-9
Comparison of MAG Planning Model Travel Times with INRIX and Microsimulation-based
DTA Travel Times .............................................................................................................8 -16
NCTCOG Model Speed Analysis ........................................................................................... 8-21
PSRC Model Speed Analysis ................................................................................................. 8-28
SANDAG Model Speed Analysis ............................................................................................ 8-35
MPO Model VHT Summary Comparison ................................................................................ 8-42
Comparison of Modeled Travel Times with Google Travel Times .......................................... 8-43
Concluding Remarks ..............................................................................................................8 -55
Chapter 9 Concluding Discussion of Study Findings and
Recommendations ............................................................................ 9-1
Perspectives on the Study Findings ......................................................................................... 9-1
User equilibrium traffic assignment models and their convergence ................................... 9-2
Feedback procedures and guidance .................................................................................. 9-3
Congested travel times produced by travel models ............................................................ 9-3
Validation of traffic assignment models .............................................................................. 9-4
Project evaluation and benefits estimation ......................................................................... 9-5
The Value of in-depth empirical review of models .............................................................. 9-5
Computational burden ........................................................................................................9 -5
Validation of travel models ................................................................................................. 9-5
Options for National Implementation ........................................................................................ 9-6
Research Suggestions .............................................................................................................9 -8