  In this paper fuzzy VRPTW with an uncertain travel time is considered.
Credibility theory is used to model the problem and specifies a preference
index at which it is desired that the travel times to reach the customers fall
into their time windows. We propose the integration of fuzzy and ant colony
system based evolutionary algorithm to solve the problem while preserving the
constraints. Computational results for certain benchmark problems having short
and long time horizons are presented to show the effectiveness of the
algorithm. Comparison between different preferences indexes have been obtained
to help the user in making suitable decisions.
