Global optimization method for mixed transportation network design problem: A mixed-integer linear programming approach

This paper proposes a global optimization algorithm for solving a mixed (continuous/discrete) transportation network design problem (MNDP), which is generally expressed as a mathematical programming with equilibrium constraint (MPEC). The upper level of the MNDP aims to optimize the network performance via both expansion of existing links and addition of new candidate links, whereas the lower level is a traditional Wardrop user equilibrium (UE) problem. In this paper, we first formulate the UE condition as a variational inequality (VI) problem, which is defined from a finite number of extreme points of a link-flow feasible region. The MNDP is approximated as a piecewise-linear programming (P-LP) problem, which is then transformed into a mixed-integer linear programming (MILP) problem. A global optimization algorithm based on a cutting constraint method is developed for solving the MILP problem. Numerical examples are given to demonstrate the efficiency of the proposed method and to compare the results with alternative algorithms reported in the literature.     

The economics of parking provision for the morning commute

In this paper, we study the economics of parking provision for the morning commute, where all the parking lots are owned and operated by private operators. The parking capacity allocations, parking fees and access times are considered in a parking market. First we solve the parking market equilibrium without regulatory intervention, revealing four types of competitive equilibrium. Only one of the four types of equilibrium, however, is found to be stable and realistic, and under it each parking area is preferred by the commuters during certain time periods. Compared to the case without parking choice, provision of parking through a competitive market is able to reduce commuters’ travel cost and queuing delay, but it does not necessarily lead to the most desirable market outcome that minimizes social cost or commuter cost. This issue can be addressed through market regulations, such as price-ceiling, capacity-floor or capacity-ceiling, and a quantity tax/subsidy regulation. It is found that both price-ceiling and quantity tax/subsidy regulations can efficiently reduce both the system cost and commuter cost under certain conditions, and help ensure the stability of the parking market. Numerical examples are also provided to illustrate these findings and furthermore, how a price ceiling or a quantity tax/subsidy should be set in a parking market under realistic model parameters.     

Urban activity spaces: Illustrations and application of a conceptual model for integrating the time and space dimensions

This work extends the conceptual argument for the use of ellipses to portray activity spaces and offers one example of how the ellipse construct can be used to analyze urban travel characteristics, based on observed trip making behavior and socio-economic variables. A problem in characterizing activity spaces has been in integrating the time and space dimensions into the same analytical framework while maintaining an understandable graphical representation of the space-time geographies envisioned by Hagerstrand and others. The ellipse allows this, as well as providing several quantifiable measures to be used for analyzing and characterizing activity spaces and urban travel behavior. In the current application, analysis of variance is used to analyze the resulting elliptic variables of 653 travelers. The results indicate that home location and household size are important factors in determining activity space characteristics and that the ellipse variables provide a different and useful approach for understanding urban travel behavior.     

Application of Learning Automata to Controller Design in Slow-Active Automobile Suspensions

This study considers a new design methodology in the context of active vehicle suspension control. The approach combines concepts from Stochastic Optimal Control with those of Learning Automata. A learning automaton effectively learns optimal control on-line in the vehicle, in an appropriate stochastic “test-track” environment. For practical application, the overwhelming advantage of this approach is that no explicit modelling is required, and considerable time savings may be expected in system development. This simulation study considers the on-line learning of optimal control in a low-bandwidth active suspension system, where control feedback is confined to a body-mounted accelerometer at each corner of the vehicle. It is shown that learning can successfully take place under a range of conditions, including the case when there is substantial transducer noise. The performance of the resulting control system is shown to depend heavily on the nature of the learning environment.     

Evaluating security of rail transit systems: A metric system approach

Crime and fear of crime is a major problem plaguing U.S. transit systems, particularly those serving large urban areas. This paper presents a normative framework for assessing rail transit security following a system-wide metric approach. The security metric can also be used to assess the marginal improvement in security as a result of improving or adopting alternative policing and monitoring strategies. The model consists of five tasks: surveying rail transit security systems, developing a rail transit security metric, assigning efficiency ratings to rail security functions, developing a composite index for the efficiency of the overall security system, and applying a probability matrix to temper the results. Efficiency ratings can be translated into probability of occurrence figures that can be used in a decision tree context to improve rail transit security.     

Optimization of tunnel tolls in land use and transport planning

The task of transport planning is to determine cost-effective methods of providing and improving mobility, which can include minimizing traffic congestion. A cost-effective solution to transport problems should consist of a land use pattern, a transport system an a set of road pricing policies that together bring demand and supply into balance in an efficient and equitable way. The conventional approach aimed to produce comprehensive, long-term plans for land use and transport in considerable detail, but tended to ignore the role of road pricing policy, thus ending up with solutions that might not be efficient or economical. This feature of sub-optimal road pricing policy is accentuated by the overall growth in car use, which has generated problems with the efficient use of road space. This paper presents a computer analysis system (or model) which will enable the analysis of coordinated tunnel toll pricing policies by optimising an “objective function” while satisfying the associated and other constraints. The possibility of integrating the optimal road pricing policies in the land use and transport planning are discussed. A case study based on Hong Kong data demonstrates the efficiency of optimizing tolls on two of the three harbour crossing tunnels in Hong Kong.     

Radioactive tracers as a tool in coastal oceanography: An overview of the MAST-52 project

Radionuclides (⁹⁹Tc, ¹²⁵Sb, ⁹⁰Sr, ¹³⁷Cs) discharged from La Hague in France have been used to trace advection and dispersion of water masses in the “European Coastal Current” from the English Channel to the Baltic. Time-series of radionuclide measurements in water samples taken in the English Channel, at the Netherlands coast, in the German North Sea sector and in Danish waters have been compared with reported discharge values. The prospects for using ¹²⁹I measured by accelerator mass spectrometry (AMS) as an oceanographic tracer have been evaluated as positive. The ⁹⁹Tc analytical procedure have been improved and background levels of ⁹⁹Tc, ¹³⁷Cs and ⁹⁰Sr in open North Atlantic seawater without influence from European discharges have been determined. An intercomparison programme have documented the quality of the measured ⁹⁹Tc and ¹²⁵Sb data. Transit times and transfer factors from La Hague to different locations in the study area have been estimated. It is concluded, that 10% of the La Hague discharge is transported through Kattegat and that 1/3 of the inflowing Kattegat bottom water originates from the coastal current. Three fundamentally different numeric models have been further developed under the project. The measured data have then been compared with values simulated by the three models. Models as well as measured data indicate, that a close coastal transport with longer transit times and often higher concentrations than seen in the open water main current is taking place. This coastal transport is important when contaminant transport is monitored. It is concluded, that the collected data gives a unique opportunity to evaluate models on advection and dispersion of coastal water masses and contaminants. The database will be made available as a tool for the evaluation of such models.     

1981 air-cargo market penetration

This paper examines the depth of air-cargo market penetration being made in the UK by the air-transport industry, following the collapse of I.A.T.A.-constructed fares a nd rates in the wake of de-regulation on the US domestic market in 1978.

It looks at statistical evidence from H.M. Customs and Excise for 1978, 1979 and 1980, and in particular makes a distribution costs analysis by comparing sea and air costs together. In the current economic climate, given today's freight rates and the fact that air-freight is rapidly turning towards bulk unitization with a frequent scheduled delivery service, a reassessment of company distribution costs could be financially beneficial to many exporters traditionally using sea transport.     

Future use of stage bus services

The reasons underlying the decline of stage bus services in the U.K. over the past 30 years seem to be well understood, and the probable future trends have been projected using a quantitative forecasting model. The model considers U.K. bus services at a very aggregate level, but it breaks the demand into specific user groups: work trips, children's travel, travel by the elderly, and all other travel, and separately for households with and without a private car. Forecasts depend very sensitively on the level of economic growth assumed, since this governs the two major factors which determine public transport use — car ownership and the cost of operating the services. If the economy could recover its historic growth rates, a further substantial decline in bus use seems inevitable under most realistic assumptions. However, with the present economic outlook, a lower growth rate seems likely to persist for some time, and in this case public transport use will become much more stable in the 1990's; a tendency which would be helped if there were large increases in fuel prices. Many of the Metropolitan Counties have adopted policies of strongly restraining future rises in fares, in some cases to the extent of freezing fares in monetary terms. The effects of such policies on both patronage and subsidies are considered here, and although much of the current political attention is focussed on controlling fares, the question of balance between fares and service levels is also discussed. Lastly, it must be admitted that these predictions are based on knowledge which is largely restricted to the short-term effects of transport policies. The nature of our uncertainty about longer-term effects, and the possible size of them, is considered in terms of sensitivity-testing of the prediction model.