The reasons why trip-timing is of interest to planners and analysts have been set out in Chapter 23 by Mahmassani. That Chapter focuses primarily on trip-timing decisions for urban commuters, dynamics of the adjustment process. In this companion Chapter, we first discuss some of the underlying theoretical issues in a little more depth, and then report on some recent models that have been developed. The reasons why people choose to travel at the times that they do are many and various. In general, they will be a combination of the need to meet "deadlines" for particular activities and the sequential planning of activities in different locations. While social scientists may find this a fruitful subject to analyse and model per se, within the transport field the interest is mainly on understanding the circumstances under which travellers might change their time of travel, particularly in response to pricing and other signals. Within time period choice modelling, there are two rather separate areas of interest, corresponding to the domain of "macro" and "micro" time shifts (a distinction originally propounded by Bates, 1996). In the case of "macro" shifts, we are looking at travellers' propensity to make quite large changes in their time of travel (e.g., from peak period to off-peak), typically in the face of peak period surcharges, such as road pricing etc. By contrast, "micro" shifts involve relatively minor adjustments to travel time, usually to avoid the worst incidence of congestion. Despite recent interest, modelling travellers' choice of when to travel remains an area of particular difficulty. However, even if an integrated methodology is some way off, there is a need to develop approximate tools which can address some aspects of the problem in the near future. Here, we pay particular attention to notation, since, without the necessary clarity, it is easy both to become confused and to reach false conclusions. For the covering abstract see ITRD E109027.
Abstract