Tollroads are only part of the overall trip: the error of our ways in past willingness to pay studies

With rare exception, actual tollroad traffic in many countries has failed to reproduce forecast traffic levels, regardless of whether the assessment is made after an initial year of operation or as long as 10 years after opening. Pundits have offered many reasons for this divergence, including optimism bias, strategic misrepresentation, the promise to equity investors of early returns on investment, errors in land use forecasts, and specific assumptions underlying the traffic assignment models used to develop traffic forecasts. One such assumption is the selection of a behaviourally meaningful value of travel time savings (VTTS) for use in a generalised cost or generalised time user benefit expression that is the main behavioural feature of the traffic assignment (route choice) model. Numerous empirical studies using stated choice experiments have designed choice sets of alternatives as if users choose a tolled route or a free route under the (implied) assumption that the tolled route is tolled for the entire trip. Reality is often very different, with a high incidence of use of a non-tolled road leading into and connecting out of a tolled link. In this paper we recognise this feature of route choice and redesign the stated choice experiment to account for it. Furthermore, this study is a follow up to a previous study undertaken before a new toll road was in place, and it benefits from real exposure to the new toll road. We find that the VTTS is noticeably reduced, and if the VTTS is a significant contributing influence on errors on traffic forecasts, then the lower estimates make sense behaviourally.     

Dynamic process model of mass effects on travel demand

Whereas transportation planners commonly predict the negative impacts of mass transportation, there is increasing empirical evidence of the existence of positive mass effects, whereby increased use of a mode by the ‘mass’ will generally increase its attractiveness for future travellers. In this paper we consider the dynamic impact of such an effect on the problem of travel demand forecasting, with particular regards to social network effects. Our proposed modelling approach is inspired by literature from social physics, evolutionary game theory and marketing. For simplicity of exposition, our model is specified for a scenario in which (a) there is a binary choice between two mobility lifestyles, referred to as car-oriented and transit-oriented, and (b) there are two population groups, where one is the “leading” or “innovative” population group and the other the “following” or “imitating” population group. This latter distinction follows the rather well-known Bass model from the marketing literature (1969). We develop the transition probabilities and transition dynamics. We illustrate with a numerical case study that despite lower intrinsic utility for the transit lifestyle, significant changes towards this lifestyle can be achieved by considering congestion, service improvements and mass effects. We further illustrate that mass effects can be positive or negative. In all cases we explore the sensitivity of our conclusions to the assumed parameter values.     

A measure of linked‐trip accessibility

The concept of accessibility has been variously interpreted as being the “nearness to places,” the “nearness to activities” and more recently the “ease of participating in activities.” With each of these qualitative interpretations, there has also been a variety of quantitative definitions of accessibility. This paper shows that many of the proposed definitions of accessibility can in fact be gathered together to form a spectrum of accessibility measures. These measures differ with respect to the factors included in their formulation and their degree of behavioural interpretation.

Existing measures of accessibility are shown to be deficient in one major aspect. That is, they assume that for any one measure of accessibility there is but one origin of trips. Thus, in estimating the accessibility of a point within a region it is assumed that all potential trips, which contribute to the accessibility of that point, start from that single point. In view of the considerable amount of evidence demonstrating the widespread, and increasing, occurrence of trip‐linking such a proposition must be viewed as being rather doubtful.

In the light of this, the paper proceeds to develop a measure of accessibility which explicitly accounts for the linking of trips. The implications of this measure, compared to a conventional unlinked‐trip accessibility measure, are discussed as are some problems which are foreseen in the practical implementation of such a measure.     

Constraint Mapping as a Means of Further Refining Saltmarsh Re-Creation Opportunities for the UK Solent Region

Based on geomorphological criteria, the Coastal Habitat Management Plan (CHaMP) for the Solent identified some 4,800 hectares of land potentially suitable for the creation of intertidal habitat, principally saltmarsh, through the use of managed realignment. Using “constraint mapping,” this study set out to illustrate that limitations to habitat re-creation through inundation are not merely geomorphological in nature. Indeed, a broad range of social, political, legal, technical, and economic constraints exist and must be evaluated in conjunction with physical parameters if the objectives of the European Birds and Habitats Directives are to be met, and so that future coastal defense policies ensure maintenance of the “favorable conservation status” of designated sites. A numerical filter system has been used to re-evaluate individual sites to establish “realistic” opportunities for compensatory saltmarsh creation in the Solent. As a result of taking into account wider socioeconomic constraints, it is clear that fewer areas are available for habitat creation purposes than were initially identified in the Solent CHaMP study.     

An inter‐Urban freight mode choice model

The Australian Railway Research and Development Organisation is conducting a study with one of its objectives being to determine factors affecting freight mode use. Part of this has included the development and calibration of freight mode choice models. This paper outlines the results obtained from the application of an Elimination‐by‐Aspects (EBA) model to this task. The paper describes the theoretical background to the EBA model, within the context of a general choice process, and then describes the results of the model when applied to three samples of shippers involved in regional freight transport.     

Transport policy scenario-building

Long-term planning decisions must be as robust as possible to withstand such changes in the policy-making environment. This calls for a new approach for identifying how policies might fare under different types of conditions and for identifying robust no-regrets strategies. This paper outlines a systematic and logical framework for the development of policy scenarios and shows how scenarios can be used in the analysis of future policy options. The article discusses how scenario analysis can be used to identify, anticipate and assess policy options for the future in an environment of uncertainty, mainly using examples of transport policy in Europe.     

A model of managers’ preferences for location of freight facilities

The paper reviews the need for a better understanding of the factors which affect the location of freight facilities, such as depots, terminals, freight forwarding centres, distribution centres, etc. The development of an Elimination by Aspects (EBA) model to analyse such location decisions by the managers of freight firms is described. The results are shown to be comparable (perhaps even superior to) those obtained with a logit model. Conclusions are drawn with respect to both the use of the EBA model to analyse freight facility location preference, and the factors which affect such preference. Five factors were found to be significant: closeness to existing customers, closeness to arterial roads, availability of suitable sites, cost of truck fleet operation, and closeness to labor.     

Transport policy for an ageing population

Mobility declines with increasing age, reflecting the onset of physical or mental infirmity, affordability of travel for those on retirement incomes, and the mal-design of the transport infrastructure and operational arrangements. With the prospect of a rapidly ageing population, it is important to address measures to promote mobility if the quality of life of older people is to be sustained. In the UK, pensioners on low incomes, who could be hindered in their travel by the cost of fares on public transport, benefit from the general availability of half price (or better) concessionary fares for local travel. A variety of measures are in place to counter the effects of age-associated disabilities that hinder mobility, including low floor buses, subsidised taxis and community transport schemes. The Disability Discrimination Act is ensuring that public services vehicles are accessible to older people with disabilities. The motor car is of increasing importance in later life, particularly for those with disabilities, and a variety of design and technological approaches are being brought to bear to maintain the mobility of older people. These various efforts undoubtedly enhance the mobility of older people. However, beyond that broad conclusion it is hard to make evidencebased judgements. There is therefore a pressing need to develop methods to evaluate developments in policy and practice.