  In this paper, we present a novel approach for fleet sizing in the context of
flash delivery, a time-sensitive delivery service that requires the fulfilment
of customer requests in minutes. Our approach effectively combines individual
delivery requests into groups and generates optimized operational plans that
can be executed by a single vehicle or autonomous robot. The groups are formed
using a modified routing approach for the flash delivery problem. Combining the
groups into operational plans is done by solving an integer linear problem. To
evaluate the effectiveness of our approach, we compare it against three
alternative methods: fixed vehicle routing, non-pooled deliveries and a
strategy encouraging the pooling of requests. The results demonstrate the value
of our proposed approach, showcasing its ability to optimize the fleet and
improve operational efficiency. Our experimental analysis is based on a
real-world dataset provided by a Dutch retailer, allowing us to gain valuable
insights into the design of flash delivery operations and to analyze the effect
of the maximum allowed delay, the number of stores to pick up goods from and
the employed cost functions.
