Travel demand model system for the information era

The emergence of new information technologies and recent advances in existing technologies have provided new dimensions for travel demand decisions. In this paper we propose a comprehensive travel demand modeling framework to identify and model the urban development decisions of firms and developers and the mobility, activity and travel decisions of individuals and households, and to develop a system of models that can be used by decision makers and planners to evaluate the effects of changes in the transportation system and development of information technologies (e.g. various tele-commuting, tele-services and Intelligent Transportation Systems).The implementation of an operational model system based on this framework is envisioned as an incremental process starting with the current best practice of disaggregate travel demand model systems. To this end, we present an activity-based model system as the first stage in the development of an operational model system.     

Market segmentation as a mechanism in allowing for variability of traveller behaviour

A major problem with aggregate transport planning models is the accounting of variability in traveller behaviour when the basic unit of analysis is the geographical traffic zone. In an attempt to allow for this variance, recent attention has been given to the role of socio-economic (user and household) characteristics in systematically identifying a homogeneous grouping of travellers with respect to the issue under study rather than restricting the grouping definition according to physical geographical criteria alone. This homogeneous grouping criterion combined eventually with a necessity to represent travel demand in a spatial context, can assist in improving our ability to explain real travel patterns by the development of an improved aggregation condition. The emphasis is on modelling homogeneous groups of travellers separately, and then relating the individual sets of results to each other to obtain an aggregate prediction of behaviour via a knowledge of the representativeness of each group contained in the total sample. This paper presents a technique to identify the relative homogeneity of travellers in accordance with a specified criterion, and illustrates its use with individual household data for the Sydney Metropolitan Area. The paper concludes with a discussion of the advantages of segmentation in operational transport planning, in particular with reference to the aggregation of disaggregate behavioural travel choice models, or movement from a micro-model of individual choice behaviour to an aggregate model of travel demanu.     

Wanting to travel,more or less: Exploring the determinants of the deficit and surfeit of personal travel

This study investigates the determinants of peoples desire to increase or decrease the amount of travel they do. We use data from 1,357 working commuters, residents of three different neighborhoods in the San Francisco Bay Area, California. The dependent variables are indicators of Relative Desired Mobility for ten categories of travel (short- and long-distance overall and by several mode- and purpose-specific categories). These variables are measured on a five-point ordinal scale ranging from much less to much more, through which the respondents indicated the amount of travel they want to do (in the category in question) compared to what they are doing now. Censored ordered probit models were developed for these variables, with explanatory variables including general travel attitudes, specific liking for travel in each of the same separate categories, objective and subjective measures of the amount currently traveled in each category, and personality, lifestyle, and socio-demographic characteristics. The results support the hypotheses that the liking for travel has a strong positive impact, and subjective qualitative assessments of mobility have a strong negative impact, on the desire to increase ones travel. Finally, a number of general types of effects on Relative Desired Mobility were identified, among them complementarity and substitution effects. The results of this study can provide policy makers and researchers with new and valuable insight into key principles that affect individual travel demand.     

A tale of two cities

Land use and transportation mutually affect each other. Unfortunately, most transportation decision making procedures assume that public agencies cannot shape future land use patterns, and that past land use practices unswervingly determine future conditions. In A Tale of Two Cities, the author surveys the correlations between land use policies and travel behavior in two Oregon cities (Portland and Hillsboro).Building on successes the City of Portland has achieved in reducing reliance on the automobile, the author outlines a recent project by 1000 Friends of Oregon, titled Making the Land Use, Transportation, Air Quality Connection (LUTRAQ). According to the author, the purpose of LUTRAQ is to replicate Portland's approach in a more suburban context. Specifically, LUTRAQ is attempting to develop a realistic land use/transportation/demand management alternative to a proposed new bypass freeway and to accurately measure that alternative for its effects on travel demand, land use, air quality, climate change, and other indices. Although LUTRAQ is a project in progress, the author provides preliminary information that suggests the alternative successfully reduces demand for single occupancy automobile travel.     

Office location — city or suburbs?

Suburban offices constitute a growing proportion of the metropolitan office stock in Melbourne. The relocation of around 1700 Coles Myer employees from the Central Business District to Tooronga, 8.5 km south east from the GPO, is an example of office decentralisation. A study of the resultant impacts arising from the relocation has been conducted utilising a before-the-move and after-the-move survey of Coles Myer employees. Both surveys generated response rates in excess of 60%. Office relocation can have various short and long term impacts on employees and will influence decisions relating to residential location, car ownership and the resultant travel and activity patterns. It is not until these impacts are quantified that planners can gain acceptance for strategies designed to minimise the negative impacts associated with dispersed employment opportunities.This paper discuses the suburbanisation of office employment in Melbourne and studies the travel related effect on the employees, whose headoffice is relocated from the CAD to a suburban location. One of the great challenges for transport in the 90's will be the successful management of office location and the resultant impacts on travel.Abbreviations CAD Central Activities District; the CAD is defined as a slightly larger area than that previously referred to as the Central Business District (CBD)     

Sample size and grouping in the estimation of disaggregate models—A simple case

Using a very simple form of disaggregate model for household car ownership, it appears that two widely held beliefs about disaggregate modelling — that analysis should always be carried out on individual households, and that sample sizes of 500 to 1000 are generally sufficient - are not necessarily valid. Though the results may not be generalizable to the full class of problems to which disaggregate analysis addresses itself, it does seem that more attention needs to be given to the questions of sample size and grouping.In addition, the standard test of goodness of fit (the so-called rho-squared test) is shown to be extremely weak. A far stronger and to some extent complementary, test is to compare the log-likelihood value given by the model with that on the basis of the full or saturated model — a test which has recently been clearly presented by a number of writers in the statistical literature. When using dummy variables, it is important that pair-wise tests on coefficients relating to various levels of the same attribute should be carried out, as well as the standard test assessing difference from zero.These points are illustrated by a number of simple examples.The abstract of this paper appears on p. 369.     

Disaggregate simultaneous urban travel demand models: A brief introduction

This paper is intended to provide a general background to the two following papers, A Simultaneous Destination and Mode Choice Model for Shopping Trips and Some Estimation Results of a Simultaneous Model of Auto Ownership and Mode Choice to Work. Some of the deficiences of the conventional urban transport modelling system are reviewed and a case is made for the use of simultaneous models estimated with disaggregate data.     

Generating complete all-day activity plans with genetic algorithms

Activity-based demand generation contructs complete all-day activity plans for each member of a population, and derives transportation demand from the fact that consecutive activities at different locations need to be connected by travel. Besides many other advantages, activity-based demand generation also fits well into the paradigm of multi-agent simulation, where each traveler is kept as an individual throughout the whole modeling process. In this paper, we present a new approach to the problem, which uses genetic algorithms (GA). Our GA keeps, for each member of the population, several instances of possible all-day activity plans in memory. Those plans are modified by mutation and crossover, while bad instances are eventually discarded. Any GA needs a fitness function to evaluate the performance of each instance. For all-day activity plans, it makes sense to use a utility function to obtain such a fitness. In consequence, a significant part of the paper is spent discussing such a utility function. In addition, the paper shows the performance of the algorithm to a few selected problems, including very busy and rather non-busy days.     

A test of the two-mode UMOT in the Netherlands

The UMOT model, presented as an alternative to conventional travel demand models, is critically examined for its feasibility to predict vehicle distance travelled and average daily traffic in The Netherlands. Using data from the National Travel Survey (OVG) 1978 a Dutch version of UMOT is developed, and an attempt is made to validate it on historical data from the period 1960 to 1980. Some comparisons are made with results of similar work using 1976 survey data in the UK by the Transport and Road Research Laboratory.     

Teleworking in the Netherlands: an evaluation of changes in travel behaviour

This article describes the first experiment on teleworking in the Netherlands, and presents the results of an analysis of the impact of teleworking on the travel behaviour of the participants in the experiment and their household members. It was concluded that teleworking has resulted in a significant decrease in the total number of trips by teleworkers (–17%). Peak-hour traffic by car has been reduced even more (–26%). An unexpected result was that the household members of the teleworkers also appeared to travel less than before the experiment.     

Model development for metro station access mode choice

This paper analyses the behaviour of metro users in choosing their access mode to a metro station. Multinominal logit models with satisfactory predictive power were developed for access mode choice on the basis of data collected by interviewing metro users at existing metro stations. A population segmentation approach was adopted and models referring to individuals having the same set of alternative access modes were developed. Trip purpose was found to have significant effects on the access mode choice. Thus, for each population segment different models are proposed for work and education and other trip purpose. Various conclusions concerning the importance of the variables included in the proposed models were drawn through comparisons carried out across the models.     

What is induced traffic?

Investment in new or up-graded roads both raises the level and alters the pattern of accessibility over the whole area served by the road system. Vehicle-users will perceive the opportunities that this increased accessibility offers and respond in various ways, most of which can lead to more rather than less travel on the system. To the extent that travel increases overall, it can be said to have been induced by the road-improvement. Conversely, congestion as it spreads on the network will deter some travel and can be said to have a traffic suppression effect.The purpose of this first paper is to spell out, as clearly as possible, what is meant by induced traffic and to relate its various components to the full range of behavioural responses by travellers. In doing so, it draws upon the recently published (December 1994) report by the Standing Advisory Committee on Trunk Road Assessment (SACTRA) and response by the UK Government. The paper concludes with some of the implications of induced/suppressed traffic for current methods of forecasting and evaluation of road investment, which are covered in more detail by subsequent authors.     

The opening of the Amsterdam Ring Road

This paper presents the results of a major before-and-after study carried out to establish the short term effects of the removal of a severe bottleneck in the road network around Amsterdam. An important focus in the study was on measuring changes in the timing of travel, as well as changes in route choice, mode choice, destination choice and frequency of travel. The results of the study indicated that, in the short run, there was little or no change in mode choice, nor was there significant emergence of new induced trips. On the other hand, large shifts in time of travel as well as route choice were reported, emphasising the importance of alterations to the timing and routes of existing trips when congestion is relieved, and the need to consider the benefits these bring in evaluating the impact of any road investment.     

An approach to the evaluation of changes in travel unreliability: A “Safety margin” hypothesis

Even where unreliability has been recognised as a significant component in the generalised cost of trip-making, few attempts have been made to quantify it in the evaluation of transport improvements. This neglect is perhaps explained by the difficulty of observing a suitable trade-off situation in which transport users can trade money directly or indirectly for improved reliability of their transport modes.This article investigates the characteristics of a possible trade-off which might be made by commuters — the allowance of extra time for travelling in order to avoid unpredictable lateness at destination. The form of the costs of a response to unreliability of this nature is considered within a more general framework of the allocation of time under uncertainty or risk conditions.Certain other approaches to the evaluation of travel unreliability are reviewed and a brief outline is given to a current research project which attempts to test the applicability of the safety margin in London commuters' timing of the trips that they take to work.Any views expressed in this article are those of the author and are not necessarily those of the Department of the Environment.     

Gateway diversity and competition in international air transportation

Because of the existence of limited designation gateways, i.e., gateways for international air travel where entry by U.S. flag carriers is limited (in many cases to only one carrier), the U.S. Civil Aeronautics Board (CAB) has announced a policy of gateway competition. This policy seeks to maximize inter-gateway competition as a goal of the carrier selection process. The paper reviews the rationale and history of this policy and the economic principles of gateway competition. After addressing exceptions where gateway competition does not enhance competitive goals, the issue of how to enforce the credibility of the bidding process in route awards is addressed. The paper concludes by identifying circumstances where competitive objectives are not advanced through application of the principle gateway competition.     

Biases in response over time in a seven-day travel diary

Data from multi-day travel or activity diaries might be biased if recording inaccuracies and tendencies for respondents to skip certain types of trips or activities increases (or decreases) from day-to-day over the diary period. One objective of the research reported here is to test for such temporal biases in a seven-day travel diary. A second objective is to calculate correction factors which can be applied to the data in the case that biases are found. The analyses were conducted using regression and analysis-of-variance techniques. The variables investigated included total trips per day, total travel time per day, and trips per day by various modes (such as walking, car driver and car passenger). Results showed that most biases per capita statistics are due to increases over time in the percentage of respondents reporting no travel at all for an entire day. However, even after accounting for this bias by measuring statistics in terms of per mobile person, there remains a decrease over time of about 3.5 percent per day in the reporting of walking trips. This appears to be the main factor in the overall bias of about one percent per day in total trips per mobile person per day. No significant differences were found among population segments in terms of the levels of their biases.     

Changes in real incomes and the demand for taxicabs

This paper comments on the possible future of the taxicab industry within the context of a familiar economic-growth model. The future capability of the taxicab industry to check increases in real costs is shown to be an important determinant in the industry's long-term viability. More importantly, the effect of rising real incomes on the demand for taxicabs is postulated also to have a strong effect on future demand. The strength of this effect and the exact position of the taxicab in the transit tree have important implications not only for the future demand for taxis but also for the more traditional modes of public transport.     

Indicators of urban accessibility: Theory and application

The concept of accessibility and its related indicators have been in use for a long time, with still diverging interpretations of their significance and formulation. In this paper, a review is made of various existing theoretical bases, with special emphasis on recent behavioural approaches. It is suggested that this theoretical framework now allows a better appraisal of accessibility indicators and precise recommendations are proposed for their practical formulation and use. Various examples are given, especially for disaggregate analysis where a calculation for a given person is proposed instead of the conventional calculation .by a given mode. Finally, the relations between accessibility and trip rate are examined; from a study made in French cities, it is suggested that accessibility is a powerful determinant of trip rate.     

The design of bus route systems — An interactive location-allocation approach

An interactive modelling approach is developed to solve the practical problem of bus route network design. Possible bus routes are identified with facilities which can be located. Zones or pairs of zones in the urban area are identified with customers who will be allocated to the established facilities. It is shown that the classical Set Covering Problem is useful under the assumption of fixed demand; the Simple Plant Location Problem is effective under the assumption of demand which is sensitive to the level of bus service provided.     

Characterization and evolution of spatial density patterns in urban areas

This paper examines the spatial patterns of population density, household automobile ownership and other socio-demographic variables that affect urban travel, as a function of distance from the central city core. Spatial density functions provide a useful characterization of urban structure, and of its evolution when taken at different time intervals. Analysis of the data from four case cities (Austin, Atlanta, Dallas, Phoenix) for 1960, 1970 and 1980 reveals continuing overall dispersion away from the traditional central core, accompanied by the densification of formerly low-density suburbs. This presents implications for high congestion levels in the densifying suburban communities, comparable to those typically associated with the CBD. In addition, the analysis has captured the continuing growth of average household automobile ownership and revealed a distinct spatial pattern that seems to be robust across the case areas considered, as well as within radial corridors in the one case that was so analyzed (Austin).List of symbols Y gross population density in census tractt - X _t distance in miles from the center of tract to the CBD - parameter representing the central business district density - y density gradient parameter - X₀, X₁, X2, and X3 locations of the knots in a three segment division of the x-axis - D_i dummy variable defined for thei-th segment - ₁ normally distributed disturbance term,a _i,b _i,c _i,d _i,i = 1, 2, 3 — parameters to be estimated - A _t area of census tractt