In this paper, we address the flowpath design issue of automated guided vehicle systems (AGVSs). In particular we concentrate on the design of unidirectional flowpaths (i.e. vehicles are restricted to travel only in one direction along a given segment of the flowpath). We have developed five different heuristics for the design of unidirectional AGVSs. We have also developed simulated annealing algorithms for the above problem. Our extensive computational results indicate that a composite heuristic (i.e. one that combines the most successful of our five heuristics) yields solutions of comparable quality in a fraction of the time required by simulated annealing. For large-size flowpath design problems, we advocate the usage of composite heuristics over simulated annealing, and in particular for the cases in which inaccurate estimates for the input data in our design problem exist