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Roundabout models, available in the literature widely, vary between one method and another. Majority of the models are solely based on circulating flow to estimate capacity. The relationship between maximum entry flow of large dual and triple lane roundabouts and their geometric and traffic characteristics is investigated here for saturated flow condition using multivariate analysis. The developed model, based on the data gathered from 13 roundabouts in Bahrain, matched the field data reasonably well. The significant predictors, out of 60 tested ones, included circulating and exiting flows, number of entry and circulating lanes, circulating and entry widths, inscribed diameter and flare length. Capacities predicted through various international models varied considerably with both the developed model and the field data. The international models were then calibrated against the model, and consequently the field data, so as to have significant match with the two. The procedure followed in developing the model and calibrating the international models consisted of eight stages. It involved identification of significant correlation of individual predictor with capacity, multivariate regression analysis, model smoothing, multi-collinearity test, redevelopment of the model after adjusting the variables causing collinearity, comparison analysis with seven known international models and calibration of the interna-tional model. While UK, aaSIDRA and French models required around 50% reduction to match the developed model and actual data; US FHWA and Swiss models required 25% reduction and US HCM and German models required just 8% adjustments. Such clear variations call for further research. The findings assist the urban plan-ners as when to shift from one type of intersection control into another involving roundabout, and vice versa.
Adjustment factor, calibration, circulating flow, exiting flow, maximum entry flow, roundabout capacity
[1] Guicheet, B., Evolution of roundabouts in France, National Roundabout Conference, TRB, Colorado, USA, 2005.
[2] Salter, R.J., Highway Traffi c Analysis and Design, 2nd edn, Macmillan: UK, 1989.
[3] Pratelli, A. & Souleyrette, R.B. Visibility, perception and roundabout safety, WIT Transactions on the Built Environment, vol. 107, Proceedings Urban Transport XV Urban Transport and the Environment, ed. Brebbia, C.A., WIT press: UK, pp. 577–588, 2009.
[4] Al-Madani, H.M.N., Dynamic vehicular delay comparison between a police-controlled round-about and a traffic signal. Transportation Res, 37A, 681–688, 2003.
[5] Taekroutok, T., Modern roundabouts for Oregon, Department of Transportation, Research Unit, OR98-SRS22: Salem, USA, 1998.
[6] Akcelik, R., Chung, E. & Besley, M., Performance of roundabouts under heavy demand condi-tions. Road Transport Res, 5(2), 36–50, 1996.Victoria, Australia.
[7] Akcelik and Associates, aaSIDRA 2.1 in put Guide: Roundabout Data, Revised Version, Akcelik and Associates Pty Ltd,: Greythorn, Melbourne, Australia, 2005.
[8] Hollis, E., Semmens. M.C. & Dennis, S.L., ARCADY: A Computer Program to Model Capacities, Queues and Delays at Roundabouts, Transport and Road Research Laboratories: Crowthorne, Report LR 940, 1982.
[9] Tenekci, G., Montgomery, F. & Wainaina, S., Roundabout capacity in adverse weather and light conditions, Transport, 163, 29–39, Proceedings of the Institution of Civil Engineers, 2010.
[10] Transportation Research Board, Highway Capacity Manual, National Research Council, TRB, SR 209: Washington D.C., 2010.
[11] Russell, E. & Rys, M., Modeling Traffi c Flows and Capacities At Roundabout, MBTC 1099, Kansas State University: Manhattan, USA, 2000.
[12] National Cooperative Highway Research Program, Appendixes to NCHRP Report 572: Round-abouts in the United States, NCHRP Web-Only Document 94, Final Report for NCHRP Project 3–65: USA, 2006.
[13] Kimber, R.M., Gap acceptance and empiricism in capacity prediction. Transportation Sci, 23(2), 100–111, 1989. doi: http://dx.doi.org/10.1287/trsc.23.2.100
[14] Russell, E. & Rys, M., Modeling Traffi c Flows and Capacities At Roundabout, MBTC 1099, Kansas State University: Manhattan, USA, 2000.
[15] Fisk, C.S., Traffic performance analysis at roundabouts. Transportation Res, 25B, 89–102, 1991. doi: http://dx.doi.org/10.1016/0191-2615(91)90016-C
[16] Boxill, S.A., An Evaluation of 3-D Traffi c Simulation Modeling Capabilities, Report 167621– 1, Center for Transportation Training and Research, Texas, Southern University: Houston, USA, 2007.
[17] Stanek, D. & Milam, R.T., High-Capacity roundabout intersection analysis: going around in circles, National Roundabout Conference, TRB, Colorado, USA, 2005.
[18] Kimber, R.M., The Traffi c Capacity of Roundabouts, TRRL, LR942, Crowthorne, Berkshire, UK, 1980.
[19] Al-Madani, H.M.N., Capacity of Large Dual And Triple-Lanes Roundabouts During Heavy Demand Conditions, Arabian Journal of Science and Engineering-Engineering, King Fahad University of Petroleum & Minerals: Dhahran, Saudi Arabia, 2012. In press.
[20] Pratelli, A., Design of modern roundabout in urban traffi c system, WIT Transactions on the Built Environment, vol. 89, Proceedings Urban Transport XII Urban Transport and the Envi-ronment. Ed. Brebbia, C. A., WIT press, UK, 2006.
[21] Jacquemart, G., Modern Roundabout Practice in the United States, Synthesis of Highway Practice 264, Transportation Research Board: Washington, D.C., USA, 1998.
[22] Crown, R.B., RODEL1: Interactive Roundabout Design (Software Manual), RODEL Software Ltd. and Council: Stoke-on-Trent, 1987.
[23] Kimber, R M. & Hollis, M., Traffi c Queues and Delays at Road Junctions, Transport and Road Research Laboratory, LR909: Crowthorne, Berkshire, UK, 1979.
[24] Robinson, B.W. & Rodegerdts, L.A., Capacity and Performance of Roundabouts: A Summary of Recommendations in the FHWA Roundabout Guide, Kitttelson & Associates, Inc., USA, 2009./ntl.bts.gov/lib/8000/8500/8596/36_29.pdf/(as on 10th Dec. 2009).
[25] National Cooperative Highway Research Programs (NCHRP), Roundabouts in the United States, NCHRP Report 572, Transportation Research Board: Washington, D.C., 2007.
[26] Transportation Research Board, Highway Capacity Manual, National Research Council, TRB, SR 209: Washington D.C., 2000.
[27] Akcelik, R., Chung, E. & Besley, M., Roundabouts: Capacity and Performance Analysis, Research Report APR 321, ARRB, Transport Research Ltd.: Vermon South, Australia, 1998.
[28] National Association of Australian State Road Authorities (NAASRA), Guide to Traffi c En-gineering Practice- Intersections at Grade, Part 5, National Association of Australian State Road Authorities: Sydney, Australia, 1998.
[29] National Association of Australian State Road Authorities (NAASRA), Guide to Traffi c Engineering Practice- Roundabouts, Part 6, AP-G11.6, National Association of Australian State Road Authorities: Sydney, Australia, 1998.
[30] Adams, M., Barker, D. & Rye, T., Roundabouts. Unit 9, BE71008: Highway Planning and Design, 3rd edn. Napier University, School of the Built Environment: Scotland, UK, 2004.
[31] German Highway Capacity Manual, Handbook for Assessing Road Traffi c Facilities (Forsc-hungsgesellschaft fur das Strassen und Verkehrswesen, Handbuch fur die Bemessung von Stra-Benverkehrsanlagen, HBS), FGSV, no. 299, Verlag Gmbh: Koln, Germany, 2001.
[32] Brilon, W., Wu, N. & Bondzio, L., Unsignalized intersections in Germany- A State of the Art, In Proceedings of the Third International Symposium on Intersections Without Traffi c Signals, M. Kyte, ed. University of Idaho: Portland, Oregon, USA, 1997.
[33] Wu, N., Capacity of shared- short lanes at unsignalized intersections, In Proceedings of the Third International Symposium on Intersections Without Traffi c Signals, M. Kyte, ed. Univer-sity of Idaho: Portland, Oregon, USA, 1997.
[34] Lough, G., Panaroma critique des models Francais de capacite des carrefours giratoires, Proceedings of the Seminar Roundabouts 92, SETRA, BP 100, F 92223 Bagneux, Nantes, France, 1992.
[35] GIRABASE, Calculation of roundabout capacity, Available at www.certu.fr (accessed June 2008).
[36] Federal Highway Administration (FHWA), Roundabouts: An Information Guide, FHWA- RD-00–067, US Department of Transport: Virginia, USA, 2000.
[37] Wardrop, J.G., The traffic capacity of weaving sections of roundabouts, Proceedings of the First International Conference on Operational research, English Universities Press: London, UK, 1957.
[38] Kadiyalli, L.R., Traffi c Engineering and Transport Planning, Khanna Publisher: New Delhi, India, 1999.
[39] Al-Madani, H.M.N., & Saad, M., Analysis of roundabout capacity under high demand fl ows. WIT Transactions on the Built Environment, vol. 107, Proceedings Urban Transport XV Urban Transport and the Environment, ed. Brebbia, C. A., WIT press: UK, pp. 223–234, 2009.
[40] Montomery, D.C. & Runger, G.C., Applied Statistics and Probability for Engineers, 3rd edn, John Wiley, Denver: USA, 2003.
[41] Wu, N.A., Universal procedure for capacity determination at unsignalized (Priority-Controlled) intersections. Transportation Res B, 35(3), 2001. USA.
[42] Seiberlich, E.L., A Formulation to Evaluate Capacity and Delay of Multilane Roundabouts in the United States for Implementation into a Trend Forecasting Model, M.Sc. Thesis, The University of Wisconsin: Milwaukee, USA, 2001.