Impact of Ramp and Mainline Flow Mix on Freeway Breakdown and Capacity Characteristics

This study examined how the mix between ramp and mainline flows influences breakdown and capacity characteristics such as: pre-breakdown flow (PBDF), queue discharge flow (QDF), queue discharge speed (QDS), breakdown duration (BDD), and capacity change after breakdown. The mix between ramp and mainline flow was represented using the Ramp Volume Ratio (RVR) which is defined as the percentage that the ramp flow is of the total merge area traffic flow. The research also examined how results may alter if the analysis adopts the plain Ramp Volume (RV) itself, as a flow mix index, instead of the RVR. Four freeway bottlenecks in Milwaukee freeway system were used in the analysis. Because merge areas can have different utilization levels or congestion intensities, bottlenecks were ranked based on the utilization of the merge influence area and treated distinctly. For bottlenecks with heavily-utilized merge-areas, both capacities (PBDF and QDF) were reduced when RVR increased. Interestingly, BDD appeared to be very sensitive to RVR. BDD was found to double, triple or almost quadruple when ramp flow comprised a higher percentage of mainline flow. For bottlenecks with moderately-utilized merge-areas, results were usually different and counter-intuitive. For some cases, increasing the RVR resulted in a capacity flow increase and BDD decrease. The adoption of the RV index instead of the RVR index altered or reversed many results and trends for all bottlenecks. The study explains the difference between RVR and RV, demonstrates the impact of merge-area utilization, and provides further recommendations.

  • Supplemental Notes:
    • This paper was sponsored by TRB committee AHB40 Highway Capacity and Quality of Service.
  • Corporate Authors:

    Transportation Research Board

    500 Fifth Street, NW
    Washington, DC  United States  20001
  • Authors:
    • Dehman, Amjad
    • Drakopoulos, Alexander
  • Conference:
  • Date: 2013


  • English

Media Info

  • Media Type: Digital/other
  • Features: Figures; References; Tables;
  • Pagination: 20p
  • Monograph Title: TRB 92nd Annual Meeting Compendium of Papers

Subject/Index Terms

Filing Info

  • Accession Number: 01473537
  • Record Type: Publication
  • Report/Paper Numbers: 13-0388
  • Files: TRIS, TRB, ATRI
  • Created Date: Feb 5 2013 12:13PM