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Two-lane Highway Analysis Methodology Enhancements Considering Commercial Trucks

Proposal Summary and Objectives

Two-lane highways are critical components of the highway system, and are continuing to see increased truck traffic along with all other components of the highway network. It is therefore essential to have analysis tools/methods that are sensitive to the unique characteristics of commercial trucks.

A significant revision to the Highway Capacity Manual (HCM) two-lane highway analysis methodology was recently completed as part of NCHRP project 17-65. This project made use of a microscopic simulation tool (SwashSim) that performs more detailed truck dynamics modeling than other simulation tools. For example, specific powertrain characteristics (engine, transmission) are used to determine tractive effort, and roadway and physical vehicle characteristics (e.g., weight, frontal area, coefficient of drag) are used to determine resistance forces. These variables are used to calculate maximum acceleration and velocity (values that, illogically, are often user inputs in simulation programs). Overall, the resulting revised methodology from this work better accounts for the unique operating characteristics of commercial trucks on traffic stream operational performance.

However, there are still several key areas in the new methodology where further investigation is needed:

• Passing lane performance for various diverge/merge rules faster/slower vehicles;
• Guidance for climbing lane design (length and return to level grade conditions);
• Effective length of passing lane;
• Capacity on non-passing lane upgrade segments when trucks are present in traffic stream.

This project aims to improve the state-of-the-art for accounting for the impact of trucks on two-lane highway operations. This will be accomplished by building on the work that was done for NCHRP Project 17-65. The issues examined in this project are ones which are very difficult and/or very expensive to study in the field. Thus, the SwashSim simulation tool will be utilized exclusively in this project. SwashSim has the ability to model a wide range of two-lane highway configurations and operational scenarios. Because of its detailed vehicle dynamics modeling approach, SwashSim is also well-suited to modeling situations that are sensitive to the impacts of commercial vehicles. Furthermore, through the work of the NCHRP Project 17-65, SwashSim went through an extensive calibration effort with field data.

Funding Amount: $85,000
Status: Complete
Duration: Jan. 11, 2019 - Jan. 11, 2020