Estimation of Capacity Drop in Highway Merging Sections

Abstract

Capacity drop, which is defined as discharge flow drop after bottleneck activation, has been frequently observed on urban highways, especially in merging sections. Maintaining high capacity on roadways is a main concern for traffic operators, theorists, and transportation modelers. Accordingly, many researchers have investigated capacity drop, yet highway capacity and discharge flow measurement methods vary, and results are not comparable. A systematic methodology is introduced for finding capacity drops by using detector data to estimate roadway capacity and discharge flow. The impact of the number of lanes on capacity drops at merging sections on highways is investigated. Results show that capacity drop is negatively related to the number of lanes. Detailed information is analyzed for individual lanes and off-ramp effect on capacity drop. Individual lane analysis supports the negative relationship between the amount of capacity drop and the number of lanes. A decrease in capacity drop is observed when the flow ratio of the off-ramp increases.

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References

Newell

G. F.

A Simplified Theory of Kinematic Waves in Highway Traffic. I: General Theory. II: Queuing at Freeway Bottlenecks. III: Multi-Destination Flows. Transportation Research Part B, Vol. 27, 1993, pp. 281–313.

Koshi

, Iwasaki

, and Ohkura

Some Findings and an Overview on Vehicular Flow Characteristics. Proc., 8th International Symposium on Transportation and Traffic Flow Theory, 1983, pp. 403–426.

Greenshields

B.D.

, Bibbins

J.R.

, Channing

W.S.

, and Miller

H. H.

A Study of Traffic Capacity. In Highway Research Board Proceedings, Vol. 14, HRB, National Research Council, Washington, D.C., 1935, pp. 448–477.

Hall

F.L.

, and Agyemang-Duah

Freeway Capacity Drop and the Definition of Capacity. In Transportation Research Record 1320, TRB, National Research Council, Washington, D.C., 1991, pp. 91–98.

Hall

F.L.

, Hurdle

V.F.

, and Banks

J. H.

Synthesis of Recent Work on the Nature of Speed-Flow and Flow-Occupancy (or Density) Relationships on Freeways. In Transportation Research Record 1365, TRB, National Research Council, Washington, D.C., 1992, pp. 12–18.

Ringert

, and Urbanik

II . Study of Freeway Bottlenecks in Texas. In Transportation Research Record 1398, TRB, National Research Council, Washington, D.C., 1993, pp. 31–41.

Cassidy

M. J.

Bivariate Relations in Nearly Stationary Highway Traffic. Transportation Research Part B, Vol. 32, 1998, pp. 49–59.

Banks

J. H.

Flow Processes at a Freeway Bottleneck. In Transportation Research Record 1287, TRB, National Research Council, Washington, D.C., 1990, pp. 20–28.

Banks

J. H.

Two-Capacity Phenomenon at Freeway Bottlenecks: A Basis for Ramp Metering? In Transportation Research Record 1320, TRB, National Research Council, Washington, D.C., 1991, pp. 83–90.

10.

Persaud

, Yagar

, and Brownlee

Exploration of the Breakdown Phenomenon in Freeway Traffic. In Transportation Research Record 1634, TRB, National Research Council, Washington, D.C., 1998, pp. 64–69.

11.

Banks

J. H.

New Approach to Bottleneck Capacity Analysis: Second Interim Report. California PATH, Berkeley, 2006.

12.

Cassidy

M.J.

, and Windover

J. R.

Methodology for Assessing Dynamics of Freeway Traffic Flow. In Transportation Research Record 1484, TRB, National Research Council, Washington, D.C., 1995, pp. 73–79.

13.

Cassidy

M.J.

, and Bertini

R. L.

Some Traffic Features at Freeway Bottlenecks. Transportation Research Part B, Vol. 33, 1999, pp. 25–42.

14.

Bertini

R.L.

, and Malik

Observed Dynamic Traffic Features on Freeway Section with Merges and Diverges. In Transportation Research Record: Journal of the Transportation Research Board, No. 1867, Transportation Research Board of the National Academies, Washington, D.C., 2004, pp. 25–35.

15.

Bertini

R.L.

, and Leal

Empirical Study of Traffic Features at a Freeway Lane Drop. ASCE Journal of Transportation Engineering, Vol. 131, No. 6, 2005, pp. 397–407.

16.

Cassidy

M.J.

, and Rudjanakanoknad

Increasing Capacity of an Isolated Merge by Metering Its On-Ramp. Transportation Research Part B, Vol. 39, 2005, pp. 896–913.

17.

Chung

, Rudjanakanoknad

, and Cassidy

M. J.

Relation Between Traffic Density and Capacity at the Freeway Bottlenecks. Transportation Research Part B, Vol. 41, 2007, pp. 82–95.

18.

Yeo

Asymmetric Microscopic Driving Behavior Theory. PhD dissertation. University of California, Berkeley, 2008.

19.

Yeo

, and Skabardonis

Proposed Asymmetric Microscopic Traffic Flow Theory. Presented at 88th Annual Meeting of the Transportation Research Board, Washington, D.C., 2009.

20.

Yeo

, and Skabardonis

Understanding Stop-and-Go Traffic in View of Asymmetric Traffic Theory. Proc., 18th International Symposium on Transportation and Traffic Theory, Hong Kong, 2009, pp. 99–115.

21.

Chen

, Skabardonis

, and Varaiya

Systematic Identification of Freeway Bottlenecks. In Transportation Research Record: Journal of the Transportation Research Board, No. 1867, Transportation Research Board of the National Academies, Washington, D.C., 2004, pp. 46–52.

22.

Highway Capacity Manual, TRB, National Research Council, Washington, D.C., 2000.

23.

Cassidy

M.J.

, Jang

, and Daganzo

C. F.

The Smoothing Effect of Carpool Lanes on Freeway Bottlenecks. California PATH, Berkeley, 2008.