Reliability and Quality of Service Evaluation Methods for Rural Highways

Rural roads are a major part of the highway system. According to FHWA (2016), rural roads are around 70% of all highway mileage; of which 98% correspond to two-lane and multi-lane highways. Often times, a rural highway goes through small communities with a variety of conditions, including adjacent land use context (e.g., agriculture farm land, light development), roadway characteristics (e.g., number of lanes, access point density, free flow speed, terrain), and traffic control (e.g., isolated signalized intersections, roundabouts). The same facility can serve multiple purposes, such as through movement or local traffic, and users, like motorists or bicyclists. The perception of quality of service of a rural highway can also vary, depending on the user and purpose. In this regard, providing a multimodal, facility-based evaluation methodology that currently does not exist is of interest to state DOTs. A significant gap in the Highway Capacity Manual (HCM), Sixth Edition (Transportation Research Board, 2016), is the facility analysis of rural roads. The HCM contains procedural analysis techniques for uninterrupted flow two-lane and multilane segments, but it does not contain a technique to analyze the capacity and level of service for rural highways with different segment types at the facility–level. The HCM also contains facility analysis techniques for other roadway types (i.e., interrupted flow urban streets and freeways), but not for rural highway facilities. Work with two-lane highways should build upon the work completed in NCHRP 17-65, “Improved Analysis of Two-Lane Highway Capacity and Operational Performance”. Currently, facility level analysis for rural highways in Germany is addressed in German HCM, however not in the United States. Given that the HCM is nationally accepted as the primary source on highway capacity and quality of service, not having a technical approach to address many of the nation’s highways is a major limitation. Another limitation of the current HCM methodology for rural highways is the analysis horizon, which is limited to a single study period. Recently, the HCM incorporated a methodology to evaluate travel time reliability for freeways and urban streets (Chapters 36 and 37), through the work of SHRP 2 Project L08, “Incorporating Travel Time Reliability into the Highway Capacity Manual”. With this approach, the analysis horizon is expanded to an extended time horizon of several weeks or months to evaluate the variability and the quality of service the facility provides to its users. Using a distribution of level of service values mimics the variability of traffic conditions on the facility and provides a better understanding of the quality of service across time. By having more appropriate level of service measures for these types of facilities, states can better allocate their scarce resources. In parallel, the AASHTO Policy on Geometric Design of Highways and Streets (commonly known as the Green Book), 7th Edition, has introduced the consideration of context classifications as an element of the geometric design process. The two new context classes supplement, but do not replace, the functional classification system. The rural class applies to roads in rural areas that are not within a developed community, while the rural town class applies to roads located in developed communities. The classification results from the NCHRP 855 Project, “An Expanded Functional Classification System for Highways and Streets”. Given the known relationship between geometric design features and traffic operations, incorporating the Green Book’s context classification into the HCM for highway capacity analyses and design is needed. The objective of this research is to develop nationally accepted capacity and quality of service reliability techniques for rural road facilities accounting for the new context and functional classifications of the Green Book, 7th edition. The intent is that the research would lead to development of a new chapter in the HCM.


  • English


  • Status: Proposed
  • Funding: $400000
  • Contract Numbers:

    Project 08-135

  • Sponsor Organizations:

    National Cooperative Highway Research Program

    Transportation Research Board
    500 Fifth Street, NW
    Washington, DC  United States  20001

    American Association of State Highway and Transportation Officials (AASHTO)

    444 North Capitol Street, NW
    Washington, DC  United States  20001

    Federal Highway Administration

    1200 New Jersey Avenue, SE
    Washington, DC  United States  20590
  • Project Managers:

    Jared, David

  • Start Date: 20190603
  • Expected Completion Date: 0
  • Actual Completion Date: 0

Subject/Index Terms

Filing Info

  • Accession Number: 01707720
  • Record Type: Research project
  • Source Agency: Transportation Research Board
  • Contract Numbers: Project 08-135
  • Files: TRB, RiP
  • Created Date: Jun 3 2019 3:17PM