Strategies for transit fleet design considering peak and off-peak periods using the single-line model

Abstract

Transit demand and traffic conditions present relevant differences between peak and offpeak periods e.g. flows, trip lengths, congestion raising a relevant strategic design choice regarding the potential use of vehicles with different sizes. Here we first revisit the optimal design using a single-line, single-fleet model, showing that buses should always run full at the peak but not always at the off-peak. Then we develop a two-fleet strategy (with different vehicle sizes) where one fleet operates the whole day and the other during the peak period only. This strategy includes holding during the peak (in order to avoid bunching) by imposing equal cycle times for both fleets. The two-fleet operation has slightly lower total costs than one-fleet, but exhibits very different effects on users' and on operators' costs across periods. A sensitivity analysis reveals the role played by various elements and shows that results are robust. Optimal one and two-fleet designs are both better than optimizing each period independently, revealing economies of time scope.