Synchronizing e-commerce city logistics with sliding time windows

The cost-effective and high-quality city logistics service is a key for the success of e-commerce enterprises. Synchronization (sync) is emerging as a typical yet challenging requirement, which asks for simultaneous deliveries of multiple products to the same customer. This paper is among the first to model the sync constraints with sliding time windows (STW). STW is a special type of time window of which only the window size is defined. Unlike traditional time windows, the start and end time of STW could be adjusted earlier or later, so long as their difference equals to the pre-defined window size. In this sense, the STW is a time constraint with partially unknown factors. Such flexibility of STW can greatly improve the efficiency of vehicle tours, because customers could be served in a more flexible sequence decided by the transporter. A novel divide and conquer based algorithm is developed to tackle the proposed problem with partially unknown time constraints. The values for STWs will dynamically be determined during the algorithm. Numerical studies show that by modelling sync requirements with STW, transportation cost could be saved as much as in half. We also carry out sensitivity analyses on the key factors such as promised sync level to customers and the complexity of online orders.