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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.

Suggested Citation

  • 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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    1. 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.
    2. Menendez, Monica & Daganzo, Carlos F., 2007. "Effects of HOV lanes on freeway bottlenecks," Transportation Research Part B: Methodological, Elsevier, vol. 41(8), pages 809-822, October.
    3. Cassidy, Michael J., 1998. "Bivariate relations in nearly stationary highway traffic," Transportation Research Part B: Methodological, Elsevier, vol. 32(1), pages 49-59, January.
    4. Newell, G. F., 1993. "A simplified theory of kinematic waves in highway traffic, part II: Queueing at freeway bottlenecks," Transportation Research Part B: Methodological, Elsevier, vol. 27(4), pages 289-303, August.
    5. 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.
    6. Dahlgren, Joy, 2002. "High-occupancy/toll lanes: where should they be implemented?," Transportation Research Part A: Policy and Practice, Elsevier, vol. 36(3), pages 239-255, March.
    7. 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.
    8. Daganzo, C. F. & Cassidy, M. J. & Bertini, R. L., 1999. "Possible explanations of phase transitions in highway traffic," Transportation Research Part A: Policy and Practice, Elsevier, vol. 33(5), pages 365-379, June.
    9. Laval, Jorge A. & Daganzo, Carlos F., 2006. "Lane-changing in traffic streams," Transportation Research Part B: Methodological, Elsevier, vol. 40(3), pages 251-264, March.
    10. Daganzo, Carlos F. & Cassidy, Michael J., 2008. "Effects of high occupancy vehicle lanes on freeway congestion," Transportation Research Part B: Methodological, Elsevier, vol. 42(10), pages 861-872, December.
    11. 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.
    12. Bertini, Robert L. & Cassidy, Michael J., 2002. "Some observed queue discharge features at a freeway bottleneck downstream of a merge," Transportation Research Part A: Policy and Practice, Elsevier, vol. 36(8), pages 683-697, October.
    13. Cassidy, Michael J. & Daganzo, Carlos F. & Jang, Kitae & Chung, Koohong, 2006. "Empirical Reassessment of Traffic Operations: Freeway Bottlenecks and the Case for HOV Lanes," Institute of Transportation Studies, Research Reports, Working Papers, Proceedings qt31h8z81t, Institute of Transportation Studies, UC Berkeley.
    14. Dahlgren, Joy, 1998. "High occupancy vehicle lanes: Not always more effective than general purpose lanes," Transportation Research Part A: Policy and Practice, Elsevier, vol. 32(2), pages 99-114, February.
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    Citations

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    Cited by:

    1. Davis, L.C., 2012. "Mitigation of congestion at a traffic bottleneck with diversion and lane restrictions," Physica A: Statistical Mechanics and its Applications, Elsevier, vol. 391(4), pages 1679-1691.
    2. repec:eee:transa:v:118:y:2018:i:c:p:25-37 is not listed on IDEAS
    3. 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.
    4. 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.
    5. 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.
    6. Zheng, Zuduo, 2014. "Recent developments and research needs in modeling lane changing," Transportation Research Part B: Methodological, Elsevier, vol. 60(C), pages 16-32.
    7. Li, Xiaopeng & Cui, Jianxun & An, Shi & Parsafard, Mohsen, 2014. "Stop-and-go traffic analysis: Theoretical properties, environmental impacts and oscillation mitigation," Transportation Research Part B: Methodological, Elsevier, vol. 70(C), pages 319-339.
    8. 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.
    9. 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.
    10. 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.
    11. 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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