The National Academies

NCHRP 17-65 [Active]

Improved Analysis of Two-Lane Highway Capacity and Operational Performance

  Project Data
Funds: $500,000
Staff Responsibility: Waseem Dekelbab
Research Agency: University of Florida
Principal Investigator: Scott Washburn, Ph.D, P.E.
Effective Date: 9/22/2014
Completion Date: 9/30/2017
Comments: Research in progress




Safe and efficient two-lane highway service is a vital component of the nation’s transportation system. Many two-lane highways serve as the primary means for rural access to urban areas and the Interstate Highway System. Two-lane highways are a unique element of the surface transportation system because, in many instances, they serve extreme conditions of access and mobility often with very little intervention from traffic control devices. Development needs on the urban fringe and rural areas can degrade two-lane highway service. Coupled with the high costs and impacts associated with widening to four-lane highways or freeways, the nation increasingly relies on these two-lane highways to serve complex combinations of transportation needs including accessing adjacent land, commuting, multi-modal accommodation, and freight movement. In essence, designers and decision makers need the ability to analyze two-lane highway service in complex circumstances to evaluate two-lane highway capacity and operational capabilities to meet diverse traveler and freight movement needs. However, current tools to evaluate existing and proposed designs are inadequate for the task.


The Highway Capacity Manual (HCM) methodology is difficult to use for an established network. The capacity and operational performance analysis methods and models for two-lane highways are dated and limited to homogenous segments that do not account for the variations in route operational characteristics (development, transition zone, signalized intersection(s), alignment, speed, volume, etc.). Furthermore, collecting sufficient amounts of two-lane highway field data to use exclusively for the development of an analysis methodology is not practical.  Simulation tools may need to be utilized. The TWOPAS simulation program, on which the current HCM methodology for two-lane analysis is based, is no longer supported. In addition, current measures of effectiveness are difficult to field measure.




The objective of this research is to (1) develop performance measures for operational and capacity analyses of two-lane highways and develop models to produce these performance measures in a 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 should lead towards a two-lane highway facilities procedure suitable for incorporation into future editions of the HCM.



The tasks must be divided into two phases. Phase I will consist of information gathering and planning tasks, culminating in the submittal of an interim report. The interim report will describe the work completed in the Phase I tasks, include a preliminary outline of any final deliverables, and provide an updated work plan for the Phase II tasks. The updated Phase II work plan should address the manner in which the proposer intends to use the information obtained in Phase I to satisfy the project objective. A face-to-face interim meeting with NCHRP will be scheduled to discuss the interim report. Work on Phase II tasks shall not begin until the report on the Phase I tasks and the updated Phase II work plan are approved by NCHRP. The project schedule should include 1 month for NCHRP review and approval of the interim report.


A kick-off teleconference between the research team and NCHRP shall be scheduled within 1 month of the contract’s execution to discuss the work plan. In addition, a detailed description of any survey or field investigation shall be submitted to NCHRP for prior review and approval.


The research plan should address, but not be limited to, the following topics:


State of the practice

  • Gaps
  • Deficiencies

 Performance measures

  • Feasible
  • Comprehensive
  • Observable
  • Quantifiable
  • User perception


  • Availability
  • Collectability
  • Adequacy
  • Validity


  • Applicable
  • Transferable
  • Comprehensive
  • Beneficial for safety analysis
  • Directly applicable to HCM


  • Guidance
  • Modification
  • Calibration
  • Validation

Additional deliverables and their submittal timing shall include, but may not be limited to:


Phase I (as early as practicable)

  • Critical review of the existing HCM methodology, including the gaps and deficiencies
  • Summary of alternative analysis methodologies
  • Catalog of alternative performance measures, with an analysis of their strengths and weaknesses
  • Catalog of viable simulation models for the analysis of two-lane highways


 With the interim report

  •  Plan for validating the selected simulation model and how it will be used to generate data for the development of an HCM-type model


End of Phase II

  • A final report documenting the conduct of the research
  • A stand alone guidelines report for improved analysis of two-lane highway capacity and operational performance


Proposers may recommend additional deliverables to support the project objective.



STATUS: Proposals have been received in response to the RFP. The panel will work together to select a contractor to perform the work.



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