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Coordinating, Developing, and Delivering Highway Transportation Innovations

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Publication Number:  FHWA-RD-00-078    Date:  January 2000
Publication Number: FHWA-RD-00-078
Date: January 2000


The Capability and Enhancement VDANL and TWOPAS for Analyzing Vehicle Performance on Upgrades and Downgrades Within IHSDM

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This report documents the results and recommendations for defining and analyzing "Vehicle Performance on Upgrades and Downgrades" on two lane rural roads. The contract objective was to develop functional requirements (and identify gaps) to enhance the capability of the Interactive Highway Safety Design Model (IHSDM) in evaluating vehicle operations on upgrades and downgrades, and to provide outputs useful for evaluating grade steepness and the location and design of climbing lanes and emergency escape ramps. The analysis procedures involve the use two simulation programs VDANL, a vehicle dynamics simulation, and TWOPAS, a traffic flow simulation. This report includes recommendations for the best approach for applying both VDANL and TWOPAS, the planned improvements to the programs, and data collection and research needed for software enhacement, calibration, verification and validation. Case studies of an example upgrade and downgrade are also included to help support the recommended enhacements.

This report gives reasonably comprehensive review of the current capabilities of VDANL and TWOPAS, and discusses relavant literature that might have some impact on future upgrades. Upgrade and downgrade test cases are included that demonstrate the current capabilities of VDANL and TWOPAS, and also highlight areas that need upgrading in order to give a more comprehensive capability for evaluating upgrade and downgrade designs. Enhacements are recommended for VDANL and TWOPAS in order to allow a comprehensive evaluation of rural, two lane upgrades and downgrades. Research needs are also cited that will help to fill in current gaps in our modeling capability.


This document is disseminated under the sponsorship of the Department of Transportation in the interest of information exchange. The United States Government assumes no liability for its contents or use thereof.

The contents do not necessarily reflect the official policy of the Department of Transportation.

This report does not constitute a standard, specification, or regulation.

The United States Government does not endorse products or manufactures. Trade and manufactures's name appear in this report only because they are considered essential to the objective of this document.



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