Modelling car availability,modal split and trip distribution by Monte-Carlo simulation: A short way to integrated models

The model used a Monte-Carlo algorithm to simulate modal split and trip distribution as an interconnected decision process at the individual level. Using census data, the individuals of a planning region are classified into situation groups, which represent significantly different decision situations with respect to socio-demographic position and territorial location. According to the theoretical framework, which emphasises mobility constraints instead of preferences, household structure and sex (time budget and car availability constraints) and work place characteristics (location constraints) are the key variables. For each situation group, decision profiles are empirically determined; these describe car availability, travel time constraints and work place distribution. Modal split and trip distribution are simulated as an interconnected individual decision process, which is stochastically determined by the location of the individual and the decision profile of his situation group.The algorithm is very sensitive and flexible and extremely well suited to electronic processing. An extended and modified version is currently being used in the preparation of regional transporation plans for several German city regions.     

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.     

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.     

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.     

Travel behaviour and the total activity pattern

In the past years the behavioural basis of travel demand models has been considerably extended. In many cases individual behaviour is taken as the starting point of the analysis. Conventional aggregate models have been complemented by disaggregate models. However, even in most disaggregate models there is still the well-known sequence of generation, distribution, mode split, and assignment. In fact, travel behaviour is isolated from other human activities, and analyzed separately. The alternative is to take the general activity pattern of individuals as the departure point, and to consider travel as a derived demand. The basis of this study are diaries, kept during a full week on the basis of quarter hours by a sample of approximately 1100 persons.First, results with respect to travel frequency and travel time are given. Secondly, the influence of car availability and degree of urbanisation on travel behaviour is studied. Next, the population is divided into five person categories, and the travel pattern and activity pattern are studied separately per person group. Finally, links between travel and other activities are tentatively established.     

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.     

Approaches to the future in U.S. urban transportation planning

In appreciation of the fact that longer-run considerations are particularly important in the development of urban transportation, during the past three decades American transportation planning has been employing increasingly sophisticated approaches to the future. This article discusses four phases in this evolution, with a given focus dominant in each period.During the first period, following on the initial provision of federal government funds for the construction of highways in and around cities, major reliance was based on simple projections of travel demand in metropolitan regions, based mainly on current patterns.This was followed by an approach which focused on an analysis of impacts on transportation systems of projected land uses, based on forecasts of population and economic growth for a target year, on the assumption that facilities were to be provided to move all vehicles that wanted to move from here to there at least possible cost.The third period was characterized by an increasing consciousness of the value of articulating national and local goals in making transportation decisions, going beyond narrow economic and mobility objectives, and including the notion of trade-offs among goals.The most recent period discussed is one characterized by rising interest in futures studies, using methods such as Delphi and cross-impact analysis and approaches such as alternative futures, as well as a search for achieving flexibility in transportation development and for means of limiting resource commitment in the face of the uncertainties of the future (keeping options open).It is pointed out that we still have a long way to go in learning how to evolve feasible images of the future, with associated explicit urban life-style goals, that come to grips with societal variety and conflicting interests.     

Making do: The effects of a mass transit strike on travel behavior

A brief transit strike in early December 1976 disrupted bus services to the city of Pittsburgh and surrounding Allegheny County. That strike provided an opportunity for testing a variety of approaches to increase ride-sharing and to reduce traffic congestion, and for examining the effect of the strike on traffic congestion and on individual travel behavior. Even though over 60% of the commuters to the CBD use transit, the effects of the strike were relatively mild. There was some increase in traffic flow into the CBD and some spreading of the peak period. The largest proportion of the transit commuters who made trips to the CBD during the strike were dropped off by a non-commuter, increasing highway traffic. The most severe impact was felt by those transit commuters who had no cars in the household; 25% of these commuters (only 3% of the total CBD commuters) stayed home from work on the first day of the strike. Most attempts to mitigate the impact of the strike had little effect, largely because most commuters were able to manage adequately during the short strike. The anticipated parking problem, on which much of the contingency planning was focused, did not emerge, largely because of the use of carpooling and drop-off mode by many of the transit users.     

The state-of-the-art of “comprehensive” planning

Planning occurs as a part of governmental operations wherever decision-making happens. For US metropolitan areas, the locuses of decision-making are multiple, ranging in scale from very small jurisdictions up through the hierarchy to state and federal levels, and in function from general governments to many special-purpose agencies — transportation, health care, education, etc. Almost all might affect or be affected by urban transportation decisions and actions. Since no one of these units of government is comprehensive in authority and activity, there is no single, centralized planning operation that is truly comprehensive. Pluralistic planning is increasingly trying to foresee and to accommodate the interactions among the various levels and functions. Instead of fragmenting, with the fragments pulled apart and insulated, we need to move toward partitioning, not merely to delimit boundaries but also to identify interfaces. This movement is hampered by the differentials in the development of the state-of-the-art of the technical planning process now used by the several levels and functional units of government. This is most advanced, and most effective, for small, homogeneous suburban jurisdictions primarily concerned with guiding and controlling physical development; it is in disarray in central cities trying to cope with social and economic problems as well as with physical deterioration; at the metropolitan scale it is highly developed technically but not very influential. There is a trend toward a network of planning activities that recognizes and facilitates interrelationships and interactions, both vertically among functional boundaries and horizontally across geographical-scale distinctions — a trend toward the comprehensive —but we have a very long way to go.Paper prepared for the Highway Research Board Conference on Organization for Continuing Urban Transportation Planning.     

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.     

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.     

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     

Evaluating employer programs encouraging the use of alternate transportation modes: Two studies

Since 1976, major Denver metropolitan area firms have been required to encourage employees to use mass transit, carpooling, bicycling, and other alternate transportation modes to commute to work. The encouragement programs of 36 firms were clearly associated with greater use of alternate transportation modes, with the portion of variance in alternate transportation use explained by differences in employer programs of approximately 15%. The effects of the programs on deterring alternate mode users from returning to solo driving are consistently weaker than their effects on persuading drivers to try alternate transportation modes initially. Recommendations for the conduct of alternate transportation encouragement programs are made, based on these and other results. In addition, two recommendations are made concerning the evaluation of encouragement programs: that aggregate percentage change in alternate transportation use should not be used as the sole measure of success, and that environmental variables such as the availability of and pressure for use of alternate transportation modes should be measured and controlled.     

Uncertain demand,modal competition and optimal price-capacity adjustments in air transportation

A new microeconomic model for the operation of an airline facing modal competition with uncertain total demand is developed to analyze optimal price capacity combinations. The novelty is the treatment of the capacity restriction, which is not viewed as affecting negatively individual preferences (e.g. probability of a full flight), but does influence aggregate utility. A mode choice model is used to represent unrestricted individual preferences assuming full availability (phone call demand); air capacity is treated as a variable that acts on the actual choice set. Restricted choices and total demand stochasticity are integrated in welfare calculations (users' benefits and profits). Numerical examples are given and results are analyzed in terms of load factors fare levels, and sensitivity to the stochasticity of requests.This research was partially funded by FONDECYT, Chile, Direction Génerale de l'Aviation Civile, France, the Andes Foundation and the Fulbright Commission.     

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.     

Car availability change in England and Wales 1971–1981

The aggregate dynamics of car ownership have overshadowed the dynamics of car ownership and availability at the personal and household level. These dynamics have only recently been investigated in more depth. This paper contributes to this work by probing a special data source, theLongitudinal Study (LS) produced by the Office of Population Censuses and Surveys, for the changes in household car availability.The paper describes the LS and explains its special format, as a Census-based ~1% sample of the population of England and Wales.The analysis focuses on the car availability dynamics of a number of groups defined by changes in their life cycle position. Special attention is given to those households where the LS member remains a dependent child throughout the study period.The results show that all studied household types increase and decrease their car holdings, but that there are patterns in this process, which vary from group to group. In particular, the size of the previous car fleet has a different influence on the current fleet size from life cycle group to life cycle group.The paper argues in its conclusion to incorporate these differentials into the further work on car ownership and car ownership change.The work reported here was performed, while the author was a staff member of the Centre for Transport Studies, Imperial College, London.     

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.     

Modelling behavioural rules for daily activity scheduling using fuzzy logic

The paper focuses on how trip time variability affects re-scheduling of daily activities. A delay in a trip or an early arrival can contribute to changes in the timing, location of the next activity, and to the deletion/addition of some activities. We propose the idea of using fuzzy logic rules to explain the effect of variability in travel time on the benefits perceived by an individual with the changes, and to model different actions that the individuals take in order to re-establish the steadiness of the existing timetable. The fuzzy model is used to handle the imprecision of the data which is unstructured text. The results show that large deviations in trip duration are more likely to induce significant changes in the timetable whereas small deviations are either ignored or translated into modified timing of the next activity. In choosing an action, greater importance is assigned to the flexibility of the following activity, to the magnitude of the trip time saving/delay, and to the duration of the next activity. Time savings are not favoured unless they can be readily transferred into additional activity time allocated to the next activity or to a new activity. The fuzzy rules based system is capable of predicting satisfactorily the strategy of coping with uncertainty in travel times and the satisfaction sensed with the change.     

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.