The motion of motor proteins on biopolymers is important for diverse biological processes. Actin, microtubules, and nucleic acids can serve as one-dimensional tracks on which motor proteins move. Motors must accumulate on filaments in sufficient density to perform their biological roles. Motor accumulation on filaments is related to extensive theoretical work on asymmetric simple exclusion processes, a class of models in which particles move on a one-dimensional (1D) lattice by biased hopping and experience excluded-volume interactions with other particles. These models have been applied to diverse examples of one-dimensional nonequilibrium transport ranging from molecular motors to vehicular and pedestrian traffic. Motor motion on cytoskeletal filaments is particularly important for biological length regulation, because numerous proteins targeted to microtubule ends modify their dynamics and can dramatically alter the length distribution. Because the mitotic spindle includes arrays of overlapping antiparallel MTs at the spindle midzone, regulation of MT overlaps is important for mitotic spindle function and cytokinesis. We are studying the density of motors on antiparallel microtubule overlaps and subsequent length regulation of the overlaps.