Mark E. T. Horn

FLEET SCHEDULING AND DISPATCHING FOR DEMAND-RESPONSIVE PASSENGER SERVICES

Abstract This paper describes a software system designed to manage the deployment of a fleet of demand-responsive passenger vehicles such as taxis or variably routed buses. Multiple modes of operation are supported both for the fleet and for individual vehicles. Booking requests can be immediate (i.e. with zero notice) or in advance of travel. An initial implementation is chosen for each incoming request, subject to time-window and other constraints, and with an objective of minimising additional travel time or maximising a surrogate for future fleet capacity. This incremental insertion scheme is supplemented by post-insert improvement procedures, a periodically executed steepest-descent improvement procedure applied to the fleet as a whole, and a “rank-homing” heuristic incorporating information about future patterns of demand. A simple objective for trip-insertion and other scheduling operations is based on localised minimisation of travel time, while an alternative incorporating occupancy ratios has a more strategic orientation. Apart from its scheduling functions, the system includes automated vehicle dispatching procedures designed to achieve a favourable combination of customer service and efficiency of vehicle deployment. Provision is made for a variety of contingencies, including travel slower or faster than expected, unexpected vehicle locations, vehicle breakdowns and trip cancellations. Simulation tests indicate that the improvement procedures yield substantial efficiencies over more naive scheduling methods and that the system will be effective in real-time applications.

Efficient modeling of travel in networks with time-varying link speeds

This paper investigates exact and approximate methods for estimating time-minimizing vehicular movements in road network models where link speeds vary over time. The assumptions made about network conditions recognize the intrinsic relationship between speed and travel duration and are substantiated by elementary methods to obtain link travel duration. The assumptions also imply a condition of FIFO consistency, which (as shown by work of Kaufman and Smith) justifies the use of Dijkstras algorithm for path-finding purposes. The paper describes several adaptations of the Dijkstra algorithm, including new variants that are addressed specifically to the dynamic conditions mentioned above. Computational tests indicate that these procedures will be useful for scheduling, modeling, and other purposes, when applied to networks of substantial size.

An automated itinerary planning system for holiday travel

This article describes a prototype travel recommender system called the Electronic Travel Planner (ETP), which prepares travel itineraries for tourists. The system is driven by models of a traveler’s preferences and requirements, and makes reference to databases containing information pertaining to tourism and travel products. Its main tasks are to select destinations for the traveler to visit, to decide which tours or attractions are to be taken, and to compose a detailed itinerary linking up the chosen components. These tasks entail difficult optimization problems, which the prototype addresses by means of an heuristic problem-solving framework. Computational tests confirm the effectiveness of the methods used, and suggest that an automated approach will be feasible in full-scale travel planning applications.

Measures of Societal Risk and Their Potential Use in Civil Aviation

This article seeks to clarify the conceptual foundations of measures of societal risk, to investigate how such measures may be used validly in commonly encountered policy contexts, and to explore the application of these measures in the field of civil aviation. The article begins by examining standard measures of societal and individual risk (SR and IR), with attention given to ethical as well as analytical considerations. A comprehensive technical analysis of SR is provided, encompassing scalar risk measures, barrier functions, and a utility-based formulation, and clarifications are offered with respect to the treatment of SR in recent publications. The policy context for SR measures is shown to be critically important, and an extension to a hierarchical setting is developed. The prospects for applying SR to civil aviation are then considered, and some technical and conceptual issues are identified. SR appears to be a useful analytical tool in this context, provided that careful attention is given to these issues.

Static and Dynamic Order Scheduling for Recreational Rental Vehicles at Tourism Holdings Limited

Tourism Holdings Limited (THL), with 14 locations in Australia and New Zealand, operates a fleet of approximately 4,000 recreational rental vehicles of many types. It allocates vehicles to bookings centrally. If demand for a particular vehicle type at a location exceeds supply, THL may substitute vehicles of similar types or relocate vehicles from other locations to the location that needs the vehicles. The static problem that THL faces daily is to determine a vehicle schedule that minimizes the tangible and intangible costs of such substitutions and relocations. The dynamic problem is to determine---sometimes as the customer waits---whether a vehicle will be available to cover a potential booking and to incorporate that booking into the schedule. The Commonwealth Scientific and Industrial Research Organisation (CSIRO) has researched, developed, and supplied software, VASS and D-VASS, to solve the static and dynamic aspects of THLs schedule creation and maintenance. This paper describes the THL problem, the systems that CSIRO implemented, and how THL embedded these systems into its operations.

Scheduling patrol boats and crews for the Royal Australian Navy

The Royal Australian Navys Patrol Boat Force carries out essential tasks in the surveillance, policing and defence of Australias coastal waters. To help the Navy make efficient use of a new generation of boats, the authors have developed optimization procedures to schedule the activities of the boats and their crews. The procedures—embodied in a software system called CBM (‘Crews, Boats, Missions’)—use simulated annealing and specialized heuristic techniques within a multi-stage problem-solving framework. Tests show that CBM is reliable in terms of solution quality, and flexible with respect to the range of scheduling conditions applied. CBM has proved valuable to the Navy as an investigatory tool, and it is planned that it should be adapted for operational use, as part of a decision support system to aid in the ongoing management of patrol boat operations.

Quantification of High Level Safety Criteria for Civil Unmanned Aircraft Systems

The civil Unmanned Aircraft System (UAS) sector is growing rapidly, with a notable orientation towards applications considered too dull, dirty, dangerous or demanding for conventionally piloted aircraft. Operations in this sector present hazards of two main kinds: to other aircraft, and to people and property overflown by UAS. Methods currently used for assessing these hazards and for managing safety and risk are less than comprehensive. This paper commences with a review of existing High Level Safety Criteria for UAS, including safety metrics, hazard metrics and risk metrics for manned aircraft operations and other modes of transportation. A set of quantified risk criteria for UAS operations is then developed, consistent with the As Low As Reasonably Practicable (ALARP) risk management framework used in current regulatory practice.

Dynamic scheduling of recreational rental vehicles with revenue management extensions

AbstractThe rental fleet scheduling problem (RFSP) arises in vehicle-rental operations that offer a wide variety of vehicle types to customers, and allow a rented vehicle to ‘migrate’ to a setdown depot other than the pickup depot. When there is a shortage of vehicles of a particular type at a depot, vehicles may be relocated to that depot, or vehicles of similar types may be substituted. The RFSP involves assigning vehicles to rentals so as to minimise the costs of these operations, and arises in both static and online contexts. The authors have adapted a well-known assignment algorithm for application in the online context. In addition, a network-flow algorithm with more comprehensive coverage of problem conditions is used to investigate the determination of rental pricing using revenue management principles. The paper concludes with an outline of the algorithms’ use in supporting the operations of a large recreational vehicle rental company.

On-Line Vehicle Routing and Scheduling With Time-Varying Travel Speeds

This article considers the application of an on-line vehicle scheduling system to road networks where travel speeds vary over time. In such conditions, the volume of path calculations needed to maintain a consistent view of vehicle deployments may be much greater than when travel speeds are invariant. The article investigates the contexts in which time-dependent estimates of travel duration are required and presents approximate methods based on the idea of reducing the number of path calculations carried out. Simulation tests show that two of the proposed approximations are robust and effective in terms of computational performance.

Strategic workforce planning for the Australian Defence Force

This paper presents a mixed integer linear programming (MILP) model to aid in planning a large, hierarchically structured workforce. The workforce (eg, all Army commissioned officers) is classified by occupational group and rank and modelled in yearly intervals. Personnel and their movements are modelled as stocks and flows, subject to constraints representing employment conditions and resource limitations. The task is to estimate personnel numbers and flows so as to minimize a composite cost function. The model’s detailed fidelity to actual conditions, and hence its value in practice, clearly exceed previous efforts in the workforce planning domain. To overcome computational challenges that arose when an MILP solver was applied directly, the authors developed an iterative solution approach, which has yielded an attractive combination of solution quality and computational performance.