Travel Budgets – A Review of Evidence and Modelling Implications.

This paper reviews the empirical data that has been put forward as evidence for the feasibility of direct forecasts of the average amounts of time and money allocated to travel, and the alternative model Craneworks wMch have been designed to exploit such forecasts. It is concluded that the evidence for the stability of aggregate travel behaviour from analyses of cross-sectional data has not yet been reconciled with the variations shown over time

The Internal Validation of a National Model of Long Distance Traffic.

During 1980/81, the Department of Transport developed a model for describing the distribution of private vehicle trips between 642 districts in Great Britain, using data from household and roadside interviews conducted in 1976 for the Regional Highways Traffic Model, and a new formulation of the gravity model, called a composite approach, in which shorter length movements were described at a finer level of zonal detail than longer movements. This report describes the results of an independent validation exercise conducted for the Department, in which the theoretical basis of the model and its the quality of its fit to base year data were examined. The report discusses model specification; input data; calibration issues; and accuracy assessment. The main problems addressed included the treatment of intrazonal and terminal costs, which was thought to be deficient; the trip-end estimates to which the model was constrained, which were shown to have substantial variability and to be biassed (though the cause of the latter could be readily removed), with some evidence of geographical under-specification; and the differences between roadside and household interview estimates. The report includes a detailed examination of the composite model specification and contains suggestions for improving the way in which such models are fitted. The main technical developments, for both theory and practice, are the methods developed for assessing the accuracy of the fitted model and for examining the quality of its fit with respect to the observed data, taking account of the variances and covariances of modelled and data values. Overall, the broad conclusion was that, whilst there appeared to be broad compatibility between modelled and onserved data in observed cells, there was clear evidence of inadequacy in certain respects, such as for example underestimation of intradistr ict trips. This work was done in co-operation with Howard Humphreys and Partners and Transportation Planning Associates, who validated the model against independent external data; their work is reported separately

Spatial Interaction Models Using Aggregated Information.

Despite their principal use as predictors of response to changing conditions, most travel demand models are estimated from data collected in single time periods. The fact of high mutual correlation between explanatory variables is perhaps the single greatest problem for the analyst, and has led to increasing use of disaggregate approaches, and a widespread recognition of the need for the 'temporal validation' of the models. Ideally, of course, such models would be estimated from data sets spanning different time periods; in practice the only historic information that is usually available is highly aggregate and incomplete. For example, the calibration of a conventional mode-splitldistribution model requires the collection of a sufficient set of zone-to-zone flows by each mode to identify the model parameters; such information will not normally exist for other time periods. However, it may happen that for previous years ticketing records and automatic traffic counts do provide information about certain specific groups of these flows. Such information is potentially useful, and may even allow a time dimension to be incorporated in the model specification. The second major use of conventional models is to Snfill' incomplete data to establish a current pattern of demand; here too estimates of aggregate quantities often exist, and could be used. In addition to such directly observed groups as flows on roads or revenue collected, there may be independent estimates of other aggregates which can also be used in the model fitting process, or in forecasts. The most familiar of these would be trip-end estimates calculated on the basis of socio-economic characteristics of households in each zone. More recently it has been suggested that the average amounts of time and money allocated to travel, so called 'travel budgets', can also be estimated directly and used to inform more detailed forecasts of travel patterns. The aims of this paper are as follows; firstly (in Section 2), it will present some recent evidence for the nature of 'travel budgets', and for the implications that the stability of these budgets has for the form of travel demand models. Secondly (in Section 3), it will outline an approach by which all of the forms of data described above may be used during the model fitting, together with a corresponding algorithm which applies to the most common form of spatial interaction model, the logit model

Travel Budgets: Evidence from a 1974 Survey.

This paper describes a sequence of exploratory models fitted to individuals' travel times and overall households' travel times, costs and generalised costs, as reported in the 1974 County Surveyors' Trip Rate Data Bank. The analyses involve an approximate allocation of travel times to those in connection with 'mandatory' activities (assumed fixed in the short term, in frequency and location) and those in connection with 'discretionary' activities (the rest). The most important 'background' variables are identified and discussed. Finally, after controlling for these background variables, a comparison is made between amounts of travel performed in connection with discretionary activities by individuals and households grouped according to reported amounts of 'mandatory' travel. Little or no variation is found, leading to the conclusion that the two sorts of travel are undertaken independently; for example, there is no indication that those reporting above-average amounts of 'mandatory' travel perform below-average amounts of 'discretionary' travel

National and international freight transport models: overview and ideas for further development

This paper contains a review of the literature on freight transport models, focussing on the types of models that have been developed since the nineties for forecasting, policy simulation and project evaluation at the national and international level. Models for production, attraction, distribution, modal split and assignment are discussed in the paper. Furthermore, the paper also includes a number of ideas for future development, especially for the regional and urban components within national freight transport models

Assessing the Value of Time Travel Savings – A Feasibility Study on Humberside.

It is expected that the opening of the Humber Bridge will cause major changes to travel patterns around Humberside; given the level of tolls as currently stated, many travellers will face decisions involving a trade-off between travel time, money outlay on tolls or fares and money outlay on private vehicle running costs; this either in the context of destination choice, mode choice or route choice. This report sets out the conclusions of a preliminary study of the feasibility of inferring values of travel time savings from observations made on the outcomes of these decisions. Methods based on aggregate data of destination choice are found t o be inefficient; a disaggregate mode choice study i s recommended, subject to caveats on sample size

(47171) 1999 TC36, A Transneptunian Triple

We present new analysis of HST images of (47171) 1999 TC36 that confirm it as a triple system. Fits to the point-spread function consistently show that the apparent primary is itself composed of two similar-sized components. The two central components, A1 and A2, can be consistently identified in each of nine epochs spread over seven years of time. In each instance the component separation, ranging from 0.023+/-0.002 to 0.031+/-0.003 arcsec, is roughly one half of the Hubble Space Telescope's diffraction limit at 606 nm. The orbit of the central pair has a semi-major axis of a~867 km with a period of P~1.9 days. These orbital parameters yield a system mass that is consistent with Msys = 12.75+/-0.06 10^18 kg derived from the orbit of the more distant secondary, component B. The diameters of the three components are dA1= 286(+45,-38) km, dA2= 265(+41,-35 km and dB= 139(+22,-18) km. The relative sizes of these components are more similar than in any other known multiple in the solar system. Taken together, the diameters and system mass yield a bulk density of p=542(+317,-211) kg m^-3. HST Photometry shows that component B is variable with an amplitude of >=0.17+/-0.05 magnitudes. Components A1 and A2 do not show variability larger than 0.08+/-0.03 magnitudes approximately consistent with the orientation of the mutual orbit plane and tidally-distorted equilibrium shapes. The system has high specific angular momentum of J/J'=0.93, comparable to most of the known Transneptunian binaries.Comment: 16 pages, 8 figures, 6 tables. Accepted to Icaru

Recent evidence on car cost and time elasticities of travel demand in Europe

Many European regions do not have traffic models that have been calibrated on data for that specific region. For such national and regional authorities that would like to have a first approximation of the travel demand impacts of changes in car cost and car travel times, the outcomes of the research project into elasticities of travel demand presented in this paper might be particularly useful. The objective of this study is not to replace detailed traffic models; if these are available we advise their use. In this paper, results are presented from a large-scale review of available evidence concerning elasticities of private car travel demand with respect to time and cost changes and from new runs with three traffic models. The focus is on countries that are member or associate member states of the European Union and on studies conducted recently (1985 and later). The car cost and car travel time elasticity outcomes presented refer to the impact on both trips and kilometres, distinguishing several modes, travel purposes, and are short versus long term

A meta-model for passenger and freight transport in Europe

On the basis of the outcomes of five disaggregate national models for passenger transport, four national models for freight transport and two European transport models, a fast and approximate meta-model for passenger and freight transport in Europe has been developed. The meta-model for passenger transport includes a detailed segmentation of the population, which makes it possible to investigate the impact of policies on many different groups of the population. The meta-model for passenger and freight transport has been applied for a reference scenario for 2020 and to simulate many elements of the European Commission’s Common Transport Policy. These policy measures were also assessed in terms of the consequences on the internal and external cost of transport