Examine Trade-Offs between Center Separation and Shoulder Width Allotment for a Given Roadway Width

Studies have shown that four-lane undivided roadways have poor safety performance compared to four-lane divided and two-lane cross-sections. Four-lane undivided rural highways experience relatively high crash frequencies—especially as traffic volumes increase—resulting in conflicts with high-speed opposite-direction vehicles. However, there is not always sufficient space within the available right-of-way to accommodate a traditional four-lane divided cross-section. Some states, including Texas, have started providing a narrow centerline buffer area that is separated by longitudinal pavement markings. This additional buffer area shifts the lateral placement of vehicles and introduces a greater physical separation between approaching vehicles. However, the provision of centerline buffer comes at a cost of reduced lane or shoulder widths. A better understanding of the benefits of center separation, lane and shoulder combinations would provide useful information to designers who make decisions on cross-sections for new and resurfaced roadway segments. he purpose of this project is to provide a practical framework that TxDOT can use to choose between cross-sectional design alternatives to optimize operational and safety performance on rural highways. This framework will incorporate variables such as traffic volume, heavy vehicle mix, speed, and access point density. Researchers will collect and analyze data for four-lane sites with centerline buffers and compare their safety and operational performances with traditional four-lane undivided sites. Additionally, this research will quantify the differences in the performance of four-lane undivided highways when compared to other cross-sectional designs. Researchers will use observed data and simulation to achieve the project objectives.


    • Status: Completed
    • Funding: $32,775
    • Contract Numbers:


    • Sponsor Organizations:

      Federal Highway Administration

      1200 New Jersey Avenue, SE
      Washington, DC  United States  20590

      Texas Department of Transportation

      125 E. 11th Street
      Austin, TX  United States  78701-2483
    • Managing Organizations:

      Texas Department of Transportation

      125 E. 11th Street
      Austin, TX  United States  78701-2483
    • Project Managers:

      Schwerdt, Tom

    • Performing Organizations:

      Texas A&M Transportation Institute (TTI)

      400 Harvey Mitchell Parkway South
      Suite 300
      College Station, TX  United States  77845-4375
    • Principal Investigators:

      Geedipally, Srinivas

    • Start Date: 20190719
    • Expected Completion Date: 20210831
    • Actual Completion Date: 0

    Subject/Index Terms

    Filing Info

    • Accession Number: 01715949
    • Record Type: Research project
    • Source Agency: Texas Department of Transportation
    • Contract Numbers: 0-7035
    • Files: RIP, STATEDOT
    • Created Date: Sep 10 2019 10:27AM