Speaker: Saif Benjaafar, University of Minnesota
Date & Time: April 15, 2022, Friday 17:00
Title: Dimensioning of On-Demand Vehicle Sharing Systems
Abstract: We consider the problem of optimal fleet sizing in an on-demand and one way vehicle sharing system. The size of the fleet must account not only for the nominal load and for the randomness in demand and rental duration but also for the randomness in the number of vehicles that are available at each location due to vehicle roaming (vehicles not returning to the same location from which they were picked up). We model the dynamics of the system using a closed queueing network and obtain explicit and closed form lower and upper bounds on the optimal number of vehicles. Specifically, we show that starting with any pair of lower and upper bounds, we can always obtain another pair of lower and upper bounds with gaps between the lower and upper bounds that are independent of demand and bounded by a function of only the prescribed service level. We show that the generated bounds are asymptotically exact under several regimes. Extensive numerical experiments show that the approximate and exact values are nearly indistinguishable for a wide range of parameter values. We use features of the bounds to construct a simple and closed form approximation that we show to be always within the generated lower and upper bounds and is exact under the asymptotic regimes considered. The approximation is highly interpretable with buffer capacity expressed in terms of three explicit terms that can be interpreted as follows: (1) standard buffer capacity that is protection against randomness in demand and rental times, (2) buffer capacity that is protection against vehicle roaming, and (3) a correction term. We show that the capacity needed to buffer against vehicle roaming can be substantial even in systems with vanishingly small demand. (The talk will draw on material from the following two papers:
Bio: Saif Benjaafar is McKnight Presidential Endowed Professor and Distinguished McKnight University Professor at the University of Minnesota. He is Head of the Department of Industrial & Systems Engineering at the University of Minnesota. He is a founding member of the Singapore University of Technology and Design where he served as Head of Engineering Systems and Design (at the rank of Dean). He is the Editor in Chief of the INFORMS journal Service Science. He has broad research interests in operations management with a current focus on sharing economy, online platforms and marketplaces, on-demand services, and smart city operations. His research has been published in leading journals such Management Science, Operations Research, and M&SOM and has been recognized by numerous awards from professional societies such as INFORMS, MSOM, and POMS. He serves on the board of director of Hourcar, a social carsharing organization. He is a Fellow of INFORMS and IISE.