Britton Hammit, Kimley-HornJiaxin Tong, Kimley-HornSanhita Lahiri, VDOT

VDOT VISSIM User Guide

2020 SimCap Meeting

January 14, 2020

Outline

• Introduction

• Overview of Contents

• Vissim 11 Evaluation

• Calibration Guidance

• Conclusions

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Purpose and Need• Supplement VDOT Traffic Operations and Safety

Analysis Manual (TOSAM).

• Provide guidance and Virginia best practices for model development and analysis.

• Maintain consistency for peer and agency review.

• Promote the quality and consistent VISSIM analysis in support of decision making for project planning and infrastructure.

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User Guide Contents• Model Development

• Model Review and Debugging

• QC Checklist

• Results and Preparation

• Calibration Guidance

• Model Scenarios

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Vissim 11 Evaluation

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Vissim 11 EvaluationObjectives• Improve understanding of Vissim 11 to

provide VDOT recommendation on its adoption for new projects.

• Provide guidelines for running legacy models in Vissim 11.

• Highlight differences in parameter sensitivities between Vissim 11 and legacy software versions.

• Update existing Vissim calibration guidance.6

Questions of Interest1. Will Vissim models calibrated in legacy

Vissim versions remain calibrated when run directly in Vissim 11?

2. Do these driving behavior model changes elicit a change in calibration guidance for specific parameters?

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Legacy Vissim Models• Compare the results of previously calibrated

models in prior versions of Vissim with the results obtained by running those models in Vissim 11.

• 10 Calibrated Models (5 Networks, AM/PM)• Models selected with varying network sizes,

network features, and operational conditions.

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Legacy Vissim Models

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Name Maintained Calibration in Vissim 11

Primary MOE Difference between

Versions

Severity of MOE Difference

Route 7 AM No Queue Length Moderate

Route 7 PM No Travel Times Substantial

Route 28 AM Yes - -

Route 28 PM No Freeway speeds Substantial

Seminary Road AM No Freeway speeds Substantial

Seminary Road PM Yes Freeway speeds Moderate

I-95 AM Yes - -

I-95 PM No Speed Criteria Moderate

Route 123 AM No Travel Times Substantial

Route 123 PM No Travel Times Substantial

Potential Causes• Unique traffic conditions

• Model development

• Model calibration

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Model Development

AM Model Calibration

PM Model Calibration

Calibration

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CalibrationAdjust these:

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CalibrationUsing these:

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Freeway Car Following Model (Wiedemann 99) – Calibration Parameters

Parameter Default Value Unit

Suggested Range

Basic Segment

Weave/Merge/Diverge Segment

CC0 Standstill distance 4.92 feet (ft) 4.5 to 5.5 >4.92

CC1 Headway time 0.9 seconds (s) 0.85 to 1.05 0.90 to 1.50

CC2 ‘Following’ variation 13.12 ft 6.56 to 22.97 13.12 to 39.37

CC3 Threshold for entering ‘following’ -8 -- Use default

CC4 Negative ‘following’ threshold -0.35 -- Use default

CC5 Positive ‘following’ threshold 0.35 -- Use default

CC6 Speed dependency of oscillation 11.44 -- Use default

CC7 Oscillation acceleration 0.82 ft/s2 Use default

CC8 Standstill acceleration 11.48 ft/s2 Use default

CC9 Acceleration at 50 mph 4.92 ft/s2 Use default

Arterial Car Following Model (Wiedemann 74) – Calibration Parameters

Parameter Default Value Unit Suggested

Range

Average standstill distance 6.56 feet (ft) 3.28 to 6.56

Additive part of safety distance 2.00 -- 2.0 to 2.2

Multiplicative part of safety distance 3.00 -- 2.8 to 3.3

CalibrationTo reach these:

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Calibration Styles

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Calibration Styles

Differences in Calibration Style

• Activation of the Cooperative Lane Change parameter at merge, diverge, and weaving segments.

• A low Safety Distance Reduction Factor.

• Activation of the Advanced Merge parameter.

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Cooperative Lane Change

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Cooperative Lane Change

Activated

Calibrated

Route 28 AM

I-95 AM

Not Activated

Uncalibrated

Route 28 PM

I-95 PM

Cooperative Lane Change

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Route 28, AM ModelCLC Activated - Calibrated

Field Vissim 9 Vissim 11 Field Vissim 9 Vissim 11

Route 28, PM ModelCLC not Activated – Not Calibrated

Safety Distance Reduction Factor

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Safety Distance Reduction Factor (SDRF)

0.25

Uncalibrated

Seminary Road AM

Route 123 AM

Route 123 PM

0.55

Calibrated

Seminary Road PM

Safety Distance Reduction Factor

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Seminary Road, PM ModelSDRF Near Default – Calibrated

Field Vissim 9 Vissim 11

Field Vissim 9 Vissim 11

Seminary Road, AM ModelSDRF Significantly Below Default

– Not Calibrated

Advanced Merge

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Advanced Merge

Activated

Calibrated

Route 28 AM

Seminary Road PM

I-95 AM

Not Activated

Uncalibrated

Route 28 PM

Seminary Road AM

I-95 PM

Summary• Models that were previously calibrated in legacy

versions of Vissim were more likely to maintain calibration in Vissim 11 when

• Cooperative Lane Change and Advanced Merge features were activated.

• Safety Distance Reduction factor was maintained at a conservative value near default.

• When converting a calibrated legacy model to Vissim 11, time and resources should be allotted to re-visit model calibration and fully QC model operations.

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Questions of Interest1. Will Vissim models calibrated in legacy

Vissim versions remain calibrated when run directly in Vissim 11?

2. Do these driving behavior model changes elicit a change in calibration guidance for specific parameters?

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Calibration Parameter Evaluation• Sensitivity analysis of parameters in Vissim 9

and 11 to study the impact of changes in parameter values on model outputs

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5 Models

17 Parameters

4 Parameter Values

Summary of Findings• Updates to lane change algorithms in Vissim 11

should yield smoother traffic flow under the default parameter settings.

• Thus, modelers should need to make fewer changes towards a more “aggressive” driving behavior settings.

• Safety Distance Reduction Factor• Lane Change Distance

• No evidence that previously-established recommendations for parameter ranges need to be revised.

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Findings Practical GuidanceEvidence that some “Calibration Styles” arepreferred over others.

• Narrowing ambiguity in the calibration process.• Improving resulting model robustness,

transferability, and consistency.

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Calibration Guidance

• Calibration parameter definitions

• Calibration plan

• Pre-Calibration set-up

• Calibration guidelines

• Calibration steps and structure27

Calibration Guidelines1. Activate cooperative lane change at all merge,

diverge, weaving segments.

2. Keep freeway car-following model parameters CC0 and CC1 consistent between all connected freeway links.

3. Freeway car-following model parameter CC2should be greater in merge, diverge, weaving segments compared to basic segments.

4. Safety Distance Reduction Factor adjustment should be a last resort in model calibration.

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CC1 Consistency

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CC1 = 0.9 sec

CC1 = 1.1 sec

CC1 = 1.2 sec

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Round 1Iterative adjustments of:• CCO/CC1• CC2 for “basic segments”• CC2 for “merge, diverge, and weaving segments”• Lane Change Distance

Round 2Iterative adjustments of:• Additional seeding conditions• Lane change deceleration parameters• Cooperative Lane Change parameters• Minimum Net Headway lane change parameter

Round 3Iterative adjustments of:• Addition of special Driving Behavior Containers• Safety Distance Reduction Factor lane change parameter

Freeway Corridor Calibration

Only if necessary

Summary

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• Model calibration will always be an iterative, trial-and-error procedure with numerous uncertainties.

• VDOT’s user guide introduces new guidelines and steps that can be used to structure this iterative procedure to improve consistency, efficiency, and model validity.

VISSIM User Guide is available at http://www.virginiadot.org/business/resources/VDOT_Vissim_UserGuide_Version2.0_Final_2020-01-10.pdf

Questions?

Britton Hammit, Kimley-HornBritton.Hammit@kimley-horn.com

Jiaxin Tong, Kimley-HornJiaxin.Tong@kimley-horn.com

Sanhita Lahiri, VDOTsanhita.lahiri@vdot.virginia.gov

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