A large proportion of two lane highways in the U.S. serve an important role in transporting goods, services and people, and with expanding urban congestion, alternate routes are consistently being sought by shipping companies. This new NCHRP project headed by Dr. Scott Washburn, a transportation faculty member at UFTI, aims to create improved analysis methods for evaluating two-lane highways. Here’s the project summary, including all the associated investigators:
Summary:
Two-lane highways account for a very significant portion of the national highway system and serve an essential function for the movement of people and goods. As urban areas continue to see growth further away from the central cities, two-lane highways in previously less developed areas are experiencing increases in traffic demand. Additionally, as urban area congestion continues to build, shipping companies are more frequently considering less congested two-lane highways in their routing decisions. The presence of commercial trucks on two-lane highways poses additional challenges for maintaining acceptable levels of operational performance due to more variance in the geometric design of these facilities and less favorable passing opportunities.
Although adding additional lanes to a two-lane highway will often address operational deficiencies with two-lane highways, such construction projects are very expensive. Having good and accurate analysis methods for two-lane highways may allow roadway design and traffic engineers to identify ways to make significant improvements to the operational performance of a two-lane highway without resorting to a full multilane configuration.
The standard reference in the U.S. for traffic analysis techniques is the Highway Capacity Manual (HCM). The HCM 2010 contains a chapter that provides an analysis methodology for two-lane highways. Unfortunately, the HCM analysis procedure falls short in several respects of providing roadway design and traffic engineers the methods they need for performing accurate and comprehensive two-lane highway facility evaluations. The current HCM analysis procedure has been criticized on several issues, such as the speed-flow relationship, appropriate service measures, treatment of large trucks, guidance on base free-flow speed estimation, accuracy of passing lane adjustments, and limitations in analysis scope.
In addition to the need for a two-lane highway analysis procedure for the HCM that improves upon its various deficiencies and limitations, the transportation engineering and roadway design profession could benefit from a modern microscopic simulation tool that includes the ability to model two-lane highways, particularly the phenomenon of passing in an oncoming lane. Given the complexity of some two-lane highway facilities, it is unreasonable to expect that a deterministic, analytic procedure will be capable of accurately analyzing all two-lane highway configurations. For complex situations that are not amenable to analysis with the new HCM procedure, analysts should be able to utilize a simulation tool to help them analyze these situations, such as is commonly done for arterial and freeway corridors. Additionally, due to time and budget limitations with this project, it will not be possible to develop a new analysis methodology for the HCM strictly from field data. Thus, it will be necessary to make extensive use of a microscopic simulation tool to meet the objectives of this project. Unfortunately, simulation tools that were commonly used for modeling two-lane highway facilities in the past are no longer viable tools for future applications, for myriad reasons.
The objective of this research is to (1) identify appropriate performance measures for operational and capacity analyses of two-lane highways and develop models to produce these performance measures in an HCM context, and (2) develop or modify a simulation-based analysis method for two-lane highways and offer guidance for when to apply a simulation versus HCM methods. The resulting methods will lead to a two-lane highway facilities procedure suitable for incorporation into a future edition of the HCM.
Project link: http://apps.trb.org/cmsfeed/TRBNetProjectDisplay.asp?ProjectID=3658.
Research Team:
Scott Washburn, University of Florida
Ahmed Al-Kaisy, Montana State University
Tapio Luttinen, Aalto University
Richard Dowling, Kittelson & Associates, Inc.
Mike Dixon*, University of Idaho
* Passed away on May 7, 2014.
For more information, contact Dr. Scott Washburn at swash@ce.ufl.edu.