Editorial - Recent Methodological Advances
Guest Editors:
Public transportation is generally considered as an economically, financially, environmentally and socially sustainable form of urban transportation in major cities (World Bank, 1996). Promoting public transportation has long been one of the top priorities for both developed (European Conference of Ministers of Transport, 1973; Pucher, 1995) and developing (Armstrong-Wright, 1993) countries, and is supported through a series of government interventions, such as public regulations, ownership restraints, operational priorities, direct or indirect subsidies, and privatization. The performance of public transportation is usually evaluated in terms of a number of important attributes such as cost, revenue, service ubiquity and reliability, patronage, and safety, ranging from a more localized perspective of "efficiency" to a wider perspective of "effectiveness" (Organisation for Economic Co-operation and Development, 1980; Fielding, 1992). An effective and efficient public transportation system benefits a society at large by reducing fuel consumption, preserving the environment, fostering development, reducing traffic congestion, improving safety, etc. However, ineffective and inefficient systems require excessive government subsidies, which impose a burden on taxpayers. Furthermore, in developing countries, poor levels of service on public transportation may lead to the vicious cycle and shift the transportation system to automobile-biased motorization at an early stage of development.
Hong Kong is a very densely populated city with about seven million people living in a total land area of 1,092 km2. Among cities of comparable GDP around the world, Hong Kong has among the lowest car ownership and highest public transportation usage levels. Over 90% of residents use public transport as their usual mode of transport. The development, maintenance, and expansion of a good public transportation system are therefore extremely important for continuous economic development in Hong Kong. To this end, a Workshop on Public Transportation was held in December 1999 to act as a forum for the exchange of expertise, knowledge and experience among overseas and local experts and researchers. A number of papers presented at the workshop are of particular interest to practicing engineers and researchers involved in the planning, design, and operation of public transportation systems. These papers are worthy of further elaboration and expansion, and of being shared with a wider spectrum of audience. Therefore, two Special Issues were called. They are devoted to the subject of public transportation and are designed to provide a broader platform for the dissemination of research findings by these authors and other experts. This is the first of the two Special Issues, focusing on the recent methodological advances in public transportation modeling and analysis. It consists of five papers and is presented as follows.
Following a stimulating introduction to the workshop, Allsop presents a conceptual framework for modeling the provision of transport with planned or market-determined public transport services. The problems are formulated as bi-level programs. General remarks on the distinction between the solutions of these bi-level programs and those in the context of traffic signal optimization are also made.
Zhou and Lam also adopt a bi-level programming approach to optimize fares for a transit system, subject to line capacity restraints; the upper-level sub-program seeks to minimize the total network travel time, whereas the lower-level sub-program is a stochastic user equilibrium transit assignment model with line capacity restraints. A heuristic solution algorithm based on sensitivity analysis is used to solve the bi-level program.
Ceder investigates the impact of routing strategies on transit network design problems and proposes a framework for the construction of two operational objective functions, taking into account passenger, operator, and community interests. The approach consists of a sequence of six components: route generation, route condensation, transit assignment, evaluation of objective functions, scenario evaluation, and multi-objective user decision.
The last two papers are concerned with the role of transit schedules in the design and operation of a transit system, based on computer simulation. Liu and Wirasinghe present a simulation model to evaluate the performance of a transit route for a fixed schedule, which was validated by a case study of the Calgary transit system. The simulation is based on a series of sub-models on link travel time, passenger arrival patterns, passenger boarding/alighting patterns, dwell time requirements and terminal time requirements. A rule-based optimization approach, comprising a mix of heuristic search, enumeration, and population ranking and selection, is also proposed to determine a near-optimized transit schedule.
Tong et al. review recent advances and prospective future research in a schedule-based approach for a dynamic transit network with fixed transit schedules and time-dependent trip demands, in which a simulation sub-model is used to evaluate the performance of a transit network. Dynamic shortest path finders and the estimation of time-dependent origin-destination matrices are critically reviewed. Cases of both deterministic and stochastic user equilibrium problems are also discussed.
Owing to the diversity of public transportation research, the papers presented in this special issue are by no means exhaustive. However, they do provide general coverage of various important areas of recent methodological advances on this subject. The editors hope that this issue will bring the latest state-of-the-art methodologies of public transportation modeling to the attention of practicing engineers and researchers, and that it will inspire and stimulate new research opportunities and efforts in the field. With the recent methodological advancements, the next question becomes one of how to apply these theories and methodologies in practice. The second Special Issue in the sequel will focus on the applications of the up-to-date methodologies for solving practical public transportation problems with real case studies.
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