Experiences with a Crew Scheduling System Based on Set Covering

Abstract

The embryonic IMPACS crew scheduling system was introduced by Parker and Smith (1), and presented in a prototype form by Wren, Smith and Miller (6) at the 1983 Workshop. The basic form is still broadly similar to that given in (6), but several enhancements have been made, and a decomposition process has been introduced to deal with large problems. The current system is described, apart from the decomposition process, by Smith and Wren (2).

A prototype of the IMPACS bus crew scheduling system was installed for London Transport in 1983. This was subject to various enhancements over the next eighteen months, and was used quite extensively by London Transport schedulers during that time. In January 1985, the completed program was accepted by London Transport, and has been used for the bulk of schedule compilation by LT andits successor, London Buses Ltd., ever since.

During 1985, IMPACS was installed for two further users, and it is now being used by nine bus companies and being actively considered by others. It has also been applied experimentally to problems of London Underground.

The basic IMPACS system has been described at previous workshops, and the development of the system is the subject of a paper to be published elsewhere. In the present paper, the concepts of IMPACS are summarised. The paper introduces a decomposition technique which has been used to great advantage in large schedules, and there follows an outline of implementations for some ten clients. Results have bettered or equalled the manual schedules in all cases.