Family changes and public transport use 1984–1987

Panel data are used to investigate what happens when people have some important transitions or changes in their life-cycle, employment status, income, or car ownership. Only three years data are available, and the pace of transition is slow: as a result relevant sample sizes are rather small. The analysis is carried out in two stages: results are given from a two year period, and these are used to generate hypotheses checked with data from the third year.It is found that in many cases the effects on mobility are different from what would be expected from cross-section data. In particular:

The Effectiveness of Coastal Zone Management in the United States

The Coastal Zone Management Effectiveness Study was undertaken between 1995 and 1997 to determine how well state coastal management programs in the United States were implementing five of the core objectives of the U.S. Coastal Zone Management Act (CZMA). The five core objectives studied were: (1) protection of estuaries and coastal wetlands; (2) protection of beaches, dunes, bluffs and rocky shores; (3) provision of public access to the shore; (4) revitalization of urban waterfronts; and (5) accommodation of seaport development (as an illustration of the policy to give priority to coastal-dependent uses). Separate articles in this issue of Coastal Management report the findings of the five studies, each dealing with one of the core objectives. Each of the articles assesses issue importance, processes and tools used, and the limited outcome data available for that objective. This article provides an overview of the purposes of the study, the methodology used, the summary findings of each study, and overall conclusions and recommendations of the study team. State coastal programs are found to be effective in addressing the five CZMA objectives examined, but this conclusion is based on very limited information about program outcomes. A more definitive conclusion will require better outcome information. Coastal managers in the United States have not agreed upon indicators of success, which severely inhibits systematic and sustained collection of outcome information. A national outcome monitoring and performance evaluation system is recommended to address these deficiencies and allow better determinations of program effectiveness in the future.     

Generalised time and the problem of equity in transport studies

The generalised time expenditure on travel,g _t, may be defined asg _t =t +m/λ where t is the amount of time spent, m is the amount of money spent, and λ is the value of time. Generalised time is expressed in units of time, unlikeg _c, the generalised cost (g _c =m + λt), which measures the same quantities in units of money. Data on all trips from two studies are analysed to show that, as household income increases, the money spent per mile travelled increases, but the time spent per mile decreases. The use of generalised time gives a different picture of the relationship between income and the total time and money spent on travel to that given by the use of generalised cost. The choice between using generalised time and generalised cost in evaluation is fundamentally a choice between assuming that the marginal utility of time and that of money is constant. The procedures at present recommended by the Department of the Environment in U.K. have elements of both assumptions, with some loss of consistency. There are some a priori reasons for expecting constant marginal utility of time to be a more plausible assumption than constant marginal utility of money. Time is, by its nature, equitably and unalterably distributed, not subject to the accidents of inheritance, theft, chance, inflation, social system or government decree. Everybody starts off with 24 hours a day. Although the amount of “free” time varies, of course, it probably varies within a much smaller range than the amount of wealth, certainly for the employed population. In allocating time between various activities, the use of words likespend, save, waste, lose, gain, and so on is a reflection of how deeply rooted in language and thought is the concept of time as a fundamental currency. This approach is strengthened by recent developments in two areas where generalised cost has been found to be a useful tool of analysis — (a) in explaining and predicting the behaviour of travellers, and (b) in evaluating the social costs and benefits arising from transport projects. Only non-working time will be considered here. It is suggested that in some circumstances generalised time would allowbehaviourally correct relationships between non-working time and money to be used in evaluation. This paper — which is a revised version of “A Hypothesis of Constant Time Outlay on Travel” (Paper F29: Planning and Transport Research and Computation Ltd. Sussex, June 1973) — is based upon work carried out with the financial support of the Social Science Research Council.     

Empirical evidence on induced traffic

Disparate evidence indicates that the provision of extra road capacity results in a greater volume of traffic. The amount of extra traffic must be heavily dependent on the context, size and location of road schemes, but an appropriate average value is given by an elasticity of traffic volume with respect to travel time of about –0.5 in the short term, and up to –1.0 in the long term. As a result, an average road improvement has induced an additional 10% of base traffic in the short term and 20% in the long term: individual schemes with induced traffic at double this level may not be very unusual, especially for peak periods. Induced traffic is particularly seen on the alternative routes that road improvements are intended to relieve.     

Car ownership and public transport use: Revisiting the interaction

At the beginning of the 1980s, it seemed that a consensus was emerging among researchers that public transport service levels, fares or quality had a small but possibly important effect on car ownership, and that this should be taken into account for those purposes where car ownership forecasts are used for developing policy on public transport or roads. Somehow, the findings faded away, and had little effect on policy thinking or on analytical techniques. The results of six surveys carried out in South Yorkshire over the period 1972 to 1991, during which there were extreme changes in public transport policy, tend to support a prima facie case for reopening the question. At the household level, car ownership rates are shown to be more volatile than is often assumed, especially in multiple car households. This volatility provides a context within which the quality of public transport provision appears to influence both the level of car ownership and the relationship between changes in the level of car ownership and changes in public transport use.     

Some issues of dynamics in forecasting travel behaviour — A discussion paper

In the next few years there is likely to be a large growth of interest in the dynamic modelling of travel behaviour. In order to try to avoid the eventual collapse of enthusiasm which has sometimes occurred with other new developments when they turn out not to provide transport planning with the hoped-for panacea, this paper aims to demonstrate the diversity of approaches which will be required to tackle the subject of dynamics. In particular, it identifies three overlapping but distinct levels at which dynamics interact with travel behaviour — microdynamics, which is concerned with the detailed scheduling of activities and travel within a day — macrodynamic modifiers, whereby changes in medium- and long-term behaviour which are often considered to be instantaneous are in fact subject to important phasing considerations — and macrodynamic processes, which deal with the overriding demographic processes of birth, ageing and death. The paper suggests approaches to the incorporation of these three topics into the forecasting of travel behaviour.     

The risk of walking

Analysis of National Travel Survey data on the amount of walking done by 17,000 individuals has shown that people spend about twenty minutes per day travelling by foot, on average. This implies a pedestrian accident rate of about 500 accidents per hundred million miles walked, a greater rate than for car drivers but less than for motor cyclists. This paper also relates accident risk to age and sex of pedestrian, time of day, day of week, and month of year. It is further shown that, for daylight hours, the average number of pedestrian accidents is approximately proportional to the product of vehicle and pedestrian flows.The authors would like to thank the Department of the Environment and the Transport and Road Research Laboratory for making available NTS and accident data respectively, and C. E. Mollart for his able assistance.