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Increasing the capacity of an isolated merge by metering its on-ramp


  • Cassidy, Michael J.
  • Rudjanakanoknad, Jittichai


Measurements taken downstream of freeway/on-ramp merges have previously shown that discharge flow diminishes when a merge becomes an isolated bottleneck. By means of observation and experiment, we show here that metering an on-ramp can recover the higher discharge flow at a merge and thereby increase the merge capacity. Detailed observations were collected at a single merge using video. These data revealed that the reductions in discharge flow are triggered by a queue that forms near the merge in the freeway shoulder lane and then spreads laterally, as drivers change lanes to maneuver around slow traffic. Our experiments show that once restrictive metering mitigated this shoulder lane queue, high outflows often returned to the median lane. High merge outflows could be restored in all freeway lanes by then relaxing the metering rate so that inflows from the on-ramp increased. Although outflows recovered in this fashion were not sustained for periods greater than 13Â min, the findings are the first real evidence that ramp metering can favorably affect the capacity of an isolated merge. Furthermore, these findings point to control strategies that might generate higher outflows for more prolonged periods and increase merge capacity even more. Finally, the findings uncover details of merge operation that are essential for developing realistic theories of merging traffic.

Suggested Citation

  • Cassidy, Michael J. & Rudjanakanoknad, Jittichai, 2005. "Increasing the capacity of an isolated merge by metering its on-ramp," Transportation Research Part B: Methodological, Elsevier, vol. 39(10), pages 896-913, December.
  • Handle: RePEc:eee:transb:v:39:y:2005:i:10:p:896-913

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    References listed on IDEAS

    1. Haj-Salem, Habib & Papageorgiou, Marcos, 1995. "Ramp metering impact on urban corridor traffic: Field results," Transportation Research Part A: Policy and Practice, Elsevier, vol. 29(4), pages 303-319, July.
    2. Cassidy, Michael J. & Bertini, Robert L., 1999. "Some traffic features at freeway bottlenecks," Transportation Research Part B: Methodological, Elsevier, vol. 33(1), pages 25-42, February.
    3. Munoz, Juan Carlos & Daganzo, Carlos F, 2002. "Fingerprinting Traffic From Static Freeway Sensors," University of California Transportation Center, Working Papers qt1mf4n2w8, University of California Transportation Center.
    4. Daganzo, Carlos F., 1995. "The cell transmission model, part II: Network traffic," Transportation Research Part B: Methodological, Elsevier, vol. 29(2), pages 79-93, April.
    5. Muñoz, Juan Carlos & Daganzo, Carlos F., 2002. "The bottleneck mechanism of a freeway diverge," Transportation Research Part A: Policy and Practice, Elsevier, vol. 36(6), pages 483-505, July.
    6. Cassidy, Michael J. & Anani, Shadi B. & Haigwood, John M., 2002. "Study of freeway traffic near an off-ramp," Transportation Research Part A: Policy and Practice, Elsevier, vol. 36(6), pages 563-572, July.
    7. Daganzo, Carlos F. & Laval, Jorge & Munoz, Juan Carlos, 2002. "Ten Strategies for Freeway Congestion Mitigation with Advanced Technologies," Institute of Transportation Studies, Research Reports, Working Papers, Proceedings qt4kd6v6qf, Institute of Transportation Studies, UC Berkeley.
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