Abstract
The capacity analysis of roundabouts in Portugal is mostly done using the UK regression method. Due to its empirical and non-explanatory nature, this method has some limitations, particularly for studying innovative layouts, which has recently motivated research in Portugal into the use of capacity methods based on gap-acceptance theory. This paper describes the results of a related project: the estimation of critical headways and follow-up times at Portuguese roundabouts. For this study, gap-acceptance data were collected at six roundabouts, in two cities, and used to estimate the parameters at each entry, for the left and right entry lanes independently. Several estimation methods were used (Siegloch, Raff, Wu, Maximum Likelihood and Logit). The results have revealed important specificities of the methods that have significant effects on the results and therefore on the capacity estimate exercises. The comparison of the estimates with reference values from several countries indicates significant differences, suggesting the existence of relevant driving style differences, which implies that locally calibrated, country-specific, parameters are required for capacity calculations.References
Kimber, R. M.: The traffic capacity of roundabouts, TRRL Report LR942, Transport and Road Research Laboratory, Crowthorne, U.K., 1980.
Fortuijn, L.: Turbo Roundabouts - Design Principles and Safety Performance, Transportation Research Record: Journal of the Transportation Research Board, Volume 2096, No. 1, 2009, pp. 16-24
Vasconcelos, A. L. P., Silva, A. B., Seco, Á. J. M., and Silva, J. P.: Estimating The Parameters of Cowan’s M3 Headway Distribution for Roundabout Capacity Analyses, The Baltic Journal of Road and Bridge Engineering, Volume VII, No. 4, 2012.
Vasconcelos, A. L. P., Silva, A. B., Seco, Á. J. M., and Rouxinol, G.: Estimation of critical headways at unsignalized intersections - a microscopic approach, Advances in Transportation Studies, Volume XXVIII - Special Issue, 2012, pp. 59-72
Hagring, O.: A further generalization of Tanner’s formula, Transportation Research Part B: Methodological, Volume 32, No. 6, 1998, pp. 423-429
Vasconcelos, A. L. P., Silva, A. B., and Seco, Á. J. M.: Capacity of normal and turbo-roundabouts – comparative analysis, Proceedings of the Institution of Civil Engineers – Transport, Volume 10.1680/tran.12.00003, 2012
Tollazzi, T., Renčelj, S., and Turnšek, S.: New type of roundabout: roundabout with “depressed” lanes for right turning – “Flower Roundabout”, Promet – Traffic & Transportation, Volume 23, No. 5, 2011, pp. 353-358
Brilon, W., Koenig, R., and Troutbeck, R. J.: Useful estimation procedures for critical gaps, Transportation Research Part A: Policy and Practice, Volume 33, No. 3-4, 1999, pp. 161-186
Rodegerdts, L., Blogg, M., Wemple, E., Myers, E., et al.: Roundabouts in the United States - NCHRP Report 572, Transportation Research Board, Washington, D.C., 2007
Weinert, A.: Estimation of Critical Gaps and Follow-Up Times at Rural Unsignalized Intersections in Germany, Fourth International Symposium on Highway Capacity, Maui, Hawaii, 2000
Siegloch, W.: Die Leistungsermittlung an Knotenpunkten ohne Lichtsignalsteuerung, Strassenbau und Strassenverkehrstechnik 154, Bundesminister für Verkehr, 1973
Raff, M. and Hart, J., A volume warrant to urban stop signs, Eno Foundation for Highway Traffic Control, Saugatuck, Conn., 1950
Wu, N.: Equilibrium of Probabilities for Estimating Distribution Function of Critical Gaps at Unsignalized Intersections, Transportation Research Record: Journal of the Transportation Research Board, Volume 2286, No. 1, 2012, pp. 49-55
Miller, A. J. and Pretty, R. L.: Overtaking on Two-Lane Rural Roads, 4th ARRB Conference, Victoria, 1968
Troutbeck, R. J.: Estimating the Critical Acceptance Gap from Traffic Movements, Research Report 92-5, Physical infrastructure centre, Queensland University of Technology, 1992
Tian, Z., Vandehey, M., Robinson, B. W., Kittelson, W., et al.: Implementing the maximum likelihood methodology to measure a driver’s critical gap, Transportation Research Part A: Policy and Practice, Volume 33, No. 3-4, 1999, pp. 187-197
Hagring, O., Rouphail, N. M., and Sørensen, H. A.: Comparison of Capacity Models for Two-Lane Roundabouts, Transportation Research Record 1852, Volume, 2003, pp. 114-123
Hagring, O.: Estimation of critical gaps in two major streams, Transportation Research Part B: Methodological, Volume 34, No. 4, 2000, pp. 293-313
Zohdy, I., Sadek, S., and Rakha, H.: Empirical Analysis of Effects of Wait Time and Rain Intensity on Driver Left-Turn Gap Acceptance Behavior, Transportation Research Record: Journal of the Transportation Research Board, Volume 2173, No. 1, 2010,
pp. 1-10
Polus, A., Shiftan, Y., and Shmueli-Lazar, S.: Evaluation of the Waiting-Time effect on Critical Gaps at Roundabouts by a Logit Model, European Journal of Transport and Infrastructure Research, Volume 5, No. 1, 2005, pp. 1-12
Davis, G. A. and Swenson, T.: Field Study of Gap Acceptance by Left-Turning Drivers, Transportation Research Record: Journal of the Transportation Research Board, Volume, No. 1899, 2004, pp. 71–75
Polus, A., Lazar, S. S., and Livneh, M.: Critical Gap as a Function of Waiting Time in Determining Roundabout Capacity, Journal of Transportation Engineering, Volume 129, No. 5, 2003, pp. 504-509
Luttinen, T.: Capacity and Level of Service at Finnish Unsignalized Intersections, Finnish Road Administration, Helsinki, 2004
Akçelik, R.: A Review of Gap-Acceptance Capacity Models, 29th Conference of Australian Institute of Transport Research (CAITR 2007), University of South Australia, Adelaide, Australia, 2007
Tanyel, S., Baran, T., and Ozuysal, M.: Applicability of Various Capacity Models for Single-Lane Roundabouts in Izmir, Turkey, Journal of Transportation Engineering, Volume 133, No. 12, 2007, pp. 647-653
Çalışkanelli, P., Özuysal, M., Tanyel, S., and Yayla, N.: Comparison of different capacity models for traffic circles, TRANSPORT, Volume 24, No. 4, 2009, pp. p. 257-264
Troutbeck, R. J.: Evaluating the Performance of a Roundabout. Australian Road Research SR 45, Australian Road Research Board, 1989
Greibe, P.: Roundabout -Design and Capacity [Denmark country report], International Roundabout Design and Capacity Seminar - 6th International Symposium on Highway Capacity, Stockholm, Sweden, 2011
Brilon, W.: Studies on Roundabouts in Germany: Lessons Learned, International Roundabout Conference, Carmel, Indiana, 2011.
Tracz, M., Chodur, J., and Ostrowski, K.: Roundabouts: Country Report - Poland, International Roundabout Design and Capacity Seminar - 6th International Symposium on Highway Capacity, Stockholm, Sweden, 2011
Tollazzi, T.: The contribution to the procedure of capacity determination at unsignalized priority-controlled intersections, Promet – Traffic, Volume 16, No. 1, 2004, pp. 31-36
Romana, M. G.: Roundabout practice and research in Spain, International Roundabout Design and Capacity Seminar - 6th International Symposium on Highway Capacity, Stockholm, Sweden, 2011