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The smoothing effect of carpool lanes on freeway bottlenecks

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  • Cassidy, Michael J.
  • Jang, Kitae
  • Daganzo, Carlos F.

Abstract

Real data show that reserving a lane for carpools on congested freeways induces a smoothing effect that is characterized by significantly higher bottleneck discharge flows (capacities) in adjacent lanes. The effect is reproducible across days and freeway sites: it was observed, without exception, in all cases tested. Predicted by an earlier theory, the effect arises because disruptive vehicle lane changing diminishes in the presence of a carpool lane. We therefore conjecture that smoothing can also be induced by other means that would reduce lane changing. The benefits can be large. Queueing analysis shows that the smoothing effect greatly reduces the times spent by people and vehicles in queues. For example, by ignoring the smoothing effect at one of the sites we analyzed one would predict that its carpool lane increased both the people-hours and the vehicle-hours traveled by well over 300%. In reality, the carpool lane reduced both measures due to smoothing. The effect is so significant that even a severely underused carpool lane can in some instances increase a freeway bottleneck's total discharge flow. This happens for the site we analyzed when carpool demand is as low as 1200Â vph.

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  • Cassidy, Michael J. & Jang, Kitae & Daganzo, Carlos F., 2010. "The smoothing effect of carpool lanes on freeway bottlenecks," Transportation Research Part A: Policy and Practice, Elsevier, vol. 44(2), pages 65-75, February.
    • Handle: RePEc:eee:transa:v:44:y:2010:i:2:p:65-75
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    References listed on IDEAS

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    Cited by:

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    2. Jang, Kitae & Cassidy, Michael J., 2011. "Dual Influences on Vehicle Speeds in Special-Use Lanes and Policy Implications," Institute of Transportation Studies, Research Reports, Working Papers, Proceedings qt0dd859tf, Institute of Transportation Studies, UC Berkeley.
    3. Lapardhaja, Servet & Jalota, Devansh & Doig, Jean & Almubarak, Abdullah & Cassidy, Michael, 2021. "Testing alternative treatments for underused carpool lanes on narrow freeways," Transportation Research Part A: Policy and Practice, Elsevier, vol. 149(C), pages 139-149.
    4. Mogens Fosgerau & Kurt Van Dender, 2013. "Road pricing with complications," Transportation, Springer, vol. 40(3), pages 479-503, May.
    5. Shan, Xiaonian & Hao, Peng & Boriboonsomsin, Kanok & Wu, Guoyuan & Barth, Matthew & Chen, Xiaohong, 2018. "Partially limited access control design for special-use freeway lanes," Transportation Research Part A: Policy and Practice, Elsevier, vol. 118(C), pages 25-37.
    6. Li, Xiang & Sun, Jian-Qiao, 2017. "Studies of vehicle lane-changing dynamics and its effect on traffic efficiency, safety and environmental impact," Physica A: Statistical Mechanics and its Applications, Elsevier, vol. 467(C), pages 41-58.
    7. Jin, Wen-Long, 2013. "A multi-commodity Lighthill–Whitham–Richards model of lane-changing traffic flow," Transportation Research Part B: Methodological, Elsevier, vol. 57(C), pages 361-377.
    8. Guler, S. Ilgin & Cassidy, Michael J., 2012. "Strategies for sharing bottleneck capacity among buses and cars," Transportation Research Part B: Methodological, Elsevier, vol. 46(10), pages 1334-1345.
    9. Boysen, Nils & Briskorn, Dirk & Schwerdfeger, Stefan & Stephan, Konrad, 2021. "Optimizing carpool formation along high-occupancy vehicle lanes," European Journal of Operational Research, Elsevier, vol. 293(3), pages 1097-1112.
    10. Zheng, Zuduo, 2014. "Recent developments and research needs in modeling lane changing," Transportation Research Part B: Methodological, Elsevier, vol. 60(C), pages 16-32.
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    12. Cassidy, Michael J. & Kim, Kwangho & Ni, Wei & Gu, Weihua, 2015. "A problem of limited-access special lanes. Part II: Exploring remedies via simulation," Transportation Research Part A: Policy and Practice, Elsevier, vol. 80(C), pages 320-329.
    13. Kim, Kwangho & Cassidy, Michael J., 2012. "A capacity-increasing mechanism in freeway traffic," Transportation Research Part B: Methodological, Elsevier, vol. 46(9), pages 1260-1272.
    14. Guler, Ilgin & Cassidy, Michael, 2010. "Deploying Underutilized Bus Lanes at Key Nodes in a Road Network," Institute of Transportation Studies, Research Reports, Working Papers, Proceedings qt3fh273s9, Institute of Transportation Studies, UC Berkeley.
    15. Jang, Kitae & Cassidy, Michael J., 2012. "Dual influences on vehicle speed in special-use lanes and critique of US regulation," Transportation Research Part A: Policy and Practice, Elsevier, vol. 46(7), pages 1108-1123.
    16. Cassidy, Michael J. & Kim, Kwangho & Ni, Wei & Gu, Weihua, 2015. "A problem of limited-access special lanes. Part I: Spatiotemporal studies of real freeway traffic," Transportation Research Part A: Policy and Practice, Elsevier, vol. 80(C), pages 307-319.

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