Reliability and accessibility : factors influencing the daily variability of door-to-door travel times. In this paper we argue that travel time reliability is an important and often underrated aspect of accessibility. For households as well as for businesses, an increase of the uncertainty of travel times is often a bigger problem than an increase of the travel times themselves. Developments such as the rise of task-combiners, time-short households, just-in-time deliveries and multi-modal transports, further exacerbate the importance of reliability. The few available data on the variability of travel times on the Dutch road network show that this variability is large. There is also indirect evidence that the reliability, especially in the Randstad, is worse than in neighbouring countries, and that the situation is quickly deteriorating. Policies that aim at maintaining or improving accessibility in the Randstad should explicitly address the effects of specific measures on the reliability. SMARA is an instrument that can be used to model such effects, by means of a Monte-Carlo-simulation that models the various factors influencing the travel time variability. More specifically, it models seasonal and day-of-week influences, weather influences, happenings and attractions, motor breakdown, accidents and road works. The paper concludes with proposals for further research, using SMARA to gain insight into the present and future reliability situation in the Netherlands and the effectivity of various policies with respect to reliability. The first results of these analysis will be presented at the colloquium. (Author/publisher)
Abstract