Travel-time models considering the operating characteristics of the storage and retrieval machine HARK HWANGt and SEONG BEAK LEEt Existing travel-time models of automated storage/retrieval systems (AS/RS) assume the average uniform velocity, ignoring the operating characteristics of storage/retrieval (S/R) machine such as the acceleration/deceleration rate and the maximum velocity. Consequently, the optimal design and schedule based on the existing models is far from optimal from the practical point of view. This paper presents continuous analytical models of travel time which integrate the operating characteristics ofS/R machine. Using a randomized assignment policy,travel times are determined for both single and dual command cycles. The models developed are examined through discrete evaluation procedures.