A GA-based household scheduler

One way of making activity-based travel analysis operational for transport planning is multi-agent micro-simulation. Modelling activity and trip generation based on individual and social characteristics are central steps in this method. The model presented here generates complete daily activity schedules based on the structure of a household and its members’ activity calendars. The model assumes that the household is another basic decision-making unit for travel demand aside from individual mobility needs. Results of the model are schedules containing complete information about activity type and sequence, locations, and means of transportation, as well as activity start times and durations. The generated schedules are the outcome of a probabilistic optimisation using genetic algorithms. This iterative method improves solutions found in a random search according to the specification of a fitness criterion, which equals utility here. It contains behavioural assumptions about individuals as well as the household level. Individual utility is derived from the number of activities and their respective durations. It is reduced by costs of travelling and penalties for late, respectively early arrival. The household level is represented directly by the utility of joint activities, and indirectly by allocation of activities and means of transportation to household members. The paper presents initial tests with a three-person household, detailing resulting schedules, and discussing run-time experiences. A sensitivity analysis of the joint utility parameter impact is also included.     

A tour-based model of travel mode choice

This paper presents a new tour-based mode choice model. The model is agent-based: both households and individuals are modelled within an object-oriented, microsimulation framework. The model is household-based in that inter-personal household constraints on vehicle usage are modelled, and the auto passenger mode is modelled as a joint decision between the driver and the passenger(s) to ride-share. Decisions are modelled using a random utility framework. Utility signals are used to communicate preferences among the agents and to make trade-offs among competing demands. Each person is assumed to choose the best combination of modes available to execute each tour, subject to auto availability constraints that are determined at the household level. The households allocations of resources (i.e., cars to drivers and drivers to ride-sharing passengers) are based on maximizing overall household utility, subject to current household resource levels. The model is activity-based: it is designed for integration within a household-based activity scheduling microsimulator. The model is both chain-based and trip-based. It is trip-based in that the ultimate output of the model is a chosen, feasible travel mode for each trip in the simulation. These trip modes are, however, determined through a chain-based analysis. A key organizing principle in the model is that if a car is to be used on a tour, it must be used for the entire chain, since the car must be returned home at the end of the tour. No such constraint, however, exists with respect to other modes such as walk and transit. The paper presents the full conceptual model and estimation results for an initial empirical prototype. Because of the complex nature of the model decision structure, choice probabilities are simulated from direct generation of random utilities rather than through an analytical probability expression.     

Evaluation,prioritization and selection of transportation investment projects in New York City

Over the last decade, a large number of high capital cost transportation projects have been proposed for the New York City Region. Many have resulted from addressing evolving capacity needs, changes in regional demographics and economics, meeting the improvements necessitated by operating century old subway systems and recognizing the impact of moving freight in a dense region. But the catalyst for bringing all of these projects to the attention of the public and all regional agencies was the tragedy of September 11, 2001. While these projects entail massive investments ($50–$60 billion), little analytical work has been carried out to measure the transportation and economic costs and benefits they entail and to categorize them accordingly. Competition among agencies to secure adequate resources to implement any of the desired projects makes such analysis necessary; yet there still remain political, vested economic interests and agency rivalry barriers to achieving this important planning objective. This paper reports the methodological approach taken by these authors for consistent and transparent project evaluation and then presents results from the ranking and prioritizing methodology. The policy underpinnings and implications of the analysis are discussed in a subsequent paper and thus only briefly touched upon here in the concluding section.     

Estimation of the Non-Linear Suspension Tyre Cornering Forces from Experimental Road Test Data

The paper discusses the application to real data of an identification procedure based on an Extended Kalman Filter, for estimating the equivalent non-linear suspension tyre cornering forces of a road vehicle from a single standard manoeuvre. In particular, both the steady-state and the dynamic handling characteristics can be evaluated.     

About the seasonal variability of the Alboran Sea circulation

Data from a mooring line deployed midway between the Alboran Island and Cape Tres Forcas are used to study the time variability of the Alboran Sea from May 1997 to May 1998. The upper layer salinity and zonal velocity present annual and semiannual cycles characterised by a minimum in spring and autumn and a maximum in summer and winter. Temperature has the opposite behaviour to that of salinity indicating changes in the presence of the Atlantic water within the Alboran Passage. A large set of SST images is used to study these cycles. The decrease of salinity and velocity in our mooring location in spring and autumn seems to be related to the eastward drifting of the Western Alboran Gyre (WAG). The increase of salinity and velocity is caused by the Atlantic current flowing south of the Alboran Island and its associated thermohaline front. Conductivity–temperature–depth (CTD) data from two cruises along the 3°W are coherent with current meters and SST interpretations.During the period analysed, summer months are characterised by the stability of the two-gyre system, while in winter, the circulation is characterised by a coastal jet flowing close to the African shore. We use sea level differences across the Strait of Gibraltar for studying the variability of the Atlantic inflow. We discuss the changes in the Alboran Sea circulation and its relation with the variability of the inertial radius of the Atlantic inflow. Though our results are speculative, we find a possible relation between the disappearance of the two-gyre system and a reversal of the circulation in Gibraltar. Longer time series are needed to conclude, but comparison with previous works makes us think that the seasonal cycle described from May 1997 to May 1998 could be the most likely one for the Alboran Sea upper layer.     

Supplying a single location from heterogeneous sources

This paper studies how items with different characteristics, and being demanded at different rates from a finite number of supply points, should be transported to a common destination. The items may differ in size and value, and the origins may differ in their spatial distribution, the kind of items they produce and the production rate. Depending on the application context, the common destination can represent a warehouse, a factory, a military base, a break-bulk terminal, a port or another kind of transportation terminal. Different kinds of items may call for separate transportation treatment if, for example, the items have sharply different inventory carrying costs or their origins are not equally scattered. On the other hand, if their characteristics are not very different, they may be transported together more cheaply because of existing economies of scale. In fact, in most applications it should be optimal to use only a few transportation systems because the economies of scale are quite strong. The paper essentially shows that origins can be ranked according to a simple criterion, and that if two origins are served together, the ones ranked in between should be served with them. A simple method for determining the optimal number of transportation systems and the sources served by each is developed. The technique is illustrated with a numerical example. The results of the paper are developed assuming that supply points do not cluster together by type and that the density of suppliers is slowly varying. In any practical application in which these assumptions are not reasonable approximations, the results of this paper should not be applied too literally. Nevertheless, they can still be used as guidelines in the search for an optimum supply strategy.     

The role of copepods in the Baikal ecosystem

This describes a study of the pelagic zone of Lake Baikal with particular reference to copepods. In addition the cycling of matter and energy in lacustrine basins is described.     

The privatization of United Kingdom seaports

The background is described to U.K. port administration and the implementation of the Conservative Goverment's privatization policy is reivewed. The objectives of privatization and the ways in which it has been achieved with trust and municipal port authorities are discussed. The paper goes on to discuss the difficulties encountered in privatizing statutory undertakings and concludes by examining the benefits port managers claim have arisen from the introduction of teh policy.     

Interval constraints for the treatment of the partial data problem in gravity model calibration

The problem of indeterminacy, in the solution parameters of the Evans-Kirby calibration model, is discussed. A proposal is made to alleviate this problem, in the case of missing data, by introducing interval constraints.     

Physical distribution from a warehouse: Vehicle coverage and inventory levels

This paper studies the costs involved in distributing items from a warehouse or depot to randomly scattered customers on a day-to-day basis. Two trade-offs are explored simultaneously. The first one arises because by accumulating large inventories at the depot it is possible to build more efficient distribution tours. This trade-off has already been explored for both distribution of goods (Burns et al., 1983) and passengers (Daganzo et al., 1977; Hendrickson, 1978). Another tradeoff, which involves the length of individual vehicle tours (Clarens and Hurdle, 1975), balances the inventory inside the vehicles against the transportation cost. Banks et al. (1982) have considered both of these tradeoffs simultaneously in the context of passenger transportation, but used a somewhat unrealistic model for vehicle routing. This paper is similar to the latter reference but uses a different routing strategy. It also illustrates how the nature of the objects carried (cheap goods, expensive goods, people, etc.) affects the optimal configuration of the distribution system and the overall distribution costs. Usually there is an optimum partitioning of the service area into districts and an optimum dispatching frequency in each district. The results can vary tremendously, depending on factors such as: the inventory carrying cost per item per unit time, the transportation costs, the demand per unit area and unit time, the average distance from the depot, the average vehicle speed and the time per stop.As an illustration of the ideas, a hypothetical limousine service from an airport is analyzed. The example is used to demonstrate how dramatically the optimal system configuration depends on the nature of the items carried.