I. Introduction
Travel-Time data are the raw elements for a number of performance measures in many transportation analyzes. They can be used in transportation planning, design and operations, and evaluation. Especially, travel-time data are critical pretrip and en route information in advanced traveler information systems. They are very informative to drivers and travelers to make decision or plan schedules. With precise travel-time prediction, a route-guidance system can suggest optimal alternate routes or warn of potential traffic congestion to users; users can then decide the best departure time or estimate their expected arrival time based on predicted travel times.