New technology and the modeling of risk-taking behavior in congested road networks Yafeng Yin a , William H.K. Lam b, * , Hitoshi Ieda c a California PATH, Institute of Transportation Studies, University of California at Berkeley, Richmond, CA 94804, USA b Department of Civil and Structural Engineering, The Hong Kong Polytechnic University, Kowloon, Hong Kong, PR China c Department of Civil Engineering, The University of Tokyo, Bunkyo-ku, Tokyo, 113-8656, Japan Abstract Intelligent transport systems provide various means to improve traffic congestion in road networks. Evaluation of the benefits of these improvements requires consideration of commutersÕ response to reliabil- ity and/or uncertainty of travel time under various circumstances. Various disruptions cause recurrent or non-recurrent congestion on road networks, which make road travel times intrinsically fluctuating and unpredictable. Confronted with such uncertain traffic conditions, commuters are known to develop some simple decision-making process to adjust their travel choices. This paper represents the decision-making process involved in departure-time and route choices as risk-taking behavior under uncertainty. An expected travel disutility function associated with commutersÕ departure-time and route choices is formu- lated with taking into account the travel delay (due the recurrent congestion), the uncertainty of travel times (due to incident-induced congestion) and the consequent early or late arrival penalty. Commuters are assumed to make decision on the departure-time and route choices on the basis of the minimal expected travel disutility. Thus the network will achieve a simultaneous route and departure-time user equilibrium, in which no commuter can decrease his or her expected disutility by unilaterally changing the route or departure-time. The equilibrium is further formulated as an equivalent nonlinear complementarity problem and is then converted into an unconstrained minimization problem with the use of a gap function suggested recently. Two algorithms based on the Nelder–Mead multidimensional simplex method and the heuristic 0968-090X/$ - see front matter Ó 2004 Elsevier Ltd. All rights reserved. doi:10.1016/j.trc.2004.07.009 * Corresponding author. Tel.: +852 2766 6045; fax: +852 2334 6389. E-mail address: cehklam@polyu.edu.hk (W.H.K. Lam). www.elsevier.com/locate/trc Transportation Research Part C 12 (2004) 171–192