Look, here comes the library van! Optimising the timetable of the mobile library service on the Isle of Wight
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Look, here comes the library van! Optimising the timetable of the mobile library service on the Isle of Wight Tanutr Rienthonga, Andrew Walkerb and Tolga Bektas¸a,* a School of Management and Centre for Operational Research, Management Science and Information Systems (CORMSIS), University of Southampton, Highfield, Southampton SO17 1BJ, UK. b Isle of Wight Council, Library HQ, 5 Mariners Way, Cowes, Isle of Wight PO31 8DP, UK.
*Corresponding author.
Abstract
This article describes an approach taken to optimise the timetable of the mobile library service operating on the Isle of Wight. The mobile library visits over 90 communities on the island, offering books, DVDs, videos and CDs, and operates on a periodic timetable. The optimisation problem is formulated as a multiple travelling salesmen model with additional time-balancing constraints on route durations. The article also shows ways in which data required for the model, in particular travel times, were gathered, and discusses practical issues arising in pre-processing the data to fit the purposes of the case study. The model is used to produce an improved timetable over the current one that implies driving time reductions of up to 25 per cent and yields routes that are better balanced in terms of time spent on the visits made each day. The model is also used to test various scenarios differing with respect to the number of locations visited and days over which the service operates. OR Insight (2011) 24, 49–62. doi:10.1057/ori.2010.17; published online 26 January 2011
Keywords: multiple travelling salesman problem; routing; integer programming; optimisation Received November 2010; accepted November 2010 after one revision
& 2011 Operational Research Society Ltd 0953-5543 OR Insight www.palgrave-journals.com/ori/
Vol. 24, 1, 49–62
Rienthong et al
Introduction The Isle of Wight Council’s Library Service serves a population of around 140 000, and among unitary authorities is in the top quartile for visits and issues. The service has a stock of just under a quarter of a million books and issues close to 1 million books, CDs, DVDs and videos every year. There are currently 28 000 active borrowers out of a population of 140 000, but the service is also used for its internet-based services, access to other council services and for a wide variety of enquiries. The Isle of Wight Council’s Library Services has 11 branches providing service for Bembridge, Brighstone, Cowes, East Cowes, Freshwater, Newport, Niton, Ryde, Sandown, Shanklin and Ventnor. The main library is the Lord Louis Library located in Newport. Figure 1 shows a map of the Isle of Wight and the main centres of population on the island. The Council also provides additional library services, namely the Mobile Library Service that visits locations on the island where there are no static libraries, and the Home Library Service that delivers to the homes of people who are unable to visit their local library because of being housebound. In addition, they also have a delivery van in order to provide facili
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