Published in IET Intelligent Transport Systems Received on 28th August 2008 Revised on 1st May 2009 doi: 10.1049/iet-its.2008.0072 Special Issue – selected papers from AATT 2008 ISSN 1751-956X Threshold- and information-based holding at multiple stops G. Bellei K. Gkoumas Dipartimento di Idraulica Trasporti e Strade, Sapienza Universita ` di Roma, Via Eudossiana, 18-00184 Rome, Italy E-mail: konstantinos.gkoumas@uniroma1.it Abstract: The objective of this study is the improvement in speed and regularity of transit systems using real-time control strategies, in particular, threshold-based and information-based vehicle holding. This objective is attained by taking into account the inherent uncertainty of transit operation, because of the random travel times and passenger arrivals at stops. A Monte Carlo simulation model of a single transit line is presented, with explicit representation of traffic lights. Both the straightforward threshold-based holding strategy and the strategy based on the availability of real-time information at stops, to take holding decision at single or multiple stops, are represented and compared, taking as a reference the results obtained by a conditional priority strategy at intersections, assumed to be given only by green extension actuated by local sensors. The results are evaluated and compared using performance indicators, coincident with waiting and on board time of transit users and with road traffic delay on transversal roads. 1 Introduction The paper focuses on intermediate capacity transit systems, a key factor in establishing a viable alternative to private car in medium-sized towns and in complementing high-capacity rapid transit in larger urban areas. The strategies aiming at improving transit performance have to be tested within the framework of an operation model, where perturbation formation and diffusion phenomena are duly represented. The impact of such phenomena on waiting times results in an increase of the headway variance, thus the regularity of operation can be improved by headway control through vehicle holding. Transit speed can be increased, while helping to keep operation regular, by applying conditional transit priority strategies at traffic lights. Conditional priority plays a role similar to vehicle holding since vehicles to which priority is denied are delayed with respect to others, so it is therefore natural, when considering different holding strategies, to compare them also with conditional priority. The modelling approach adopted in this study involves Monte Carlo simulation, implemented by repeatedly drawing the outcome of the main random phenomena, such as the arrival of passengers at stops, the alighting from transit vehicles and the running time between stops, which are given as input to the operation model, to obtain a random drawing of the whole operation pattern. Consequently, the average performance of different holding strategies can be evaluated. To this aim, the traffic delay because of transit priority is computed as well, on the basis of a deterministic representation of queuing at intersections. In addition to a standard threshold-based holding strategy, a strategy aiming at equalising the headway of the controlled vehicle to that of the next one is represented. This strategy is implemented by an intelligent transportation system, since it is based on real-time information to forecast future events and take holding decision. 2 Literature review This study principally utilises premises from the field of operation models. A review of transit-related issues at various planning levels can be found in the survey paper by Desaulniers and Hickman [1]. The same authors also give a general review of control methods applied in the presence of irregularity, even if, as they state, ‘in normal service with only minor perturbations from the schedule and small service disruptions, vehicle holding and transit signal priority are the most common techniques that are applied’. Several transit line operation models have been studied in order to apply such 304 IET Intell. Transp. Syst., 2009, Vol. 3, Iss. 3, pp. 304–313 & The Institution of Engineering and Technology 2009 doi: 10.1049/iet-its.2008.0072 www.ietdl.org Authorized licensed use limited to: Universitaet Goettingen. Downloaded on November 2, 2009 at 09:55 from IEEE Xplore. Restrictions apply.