In a second area of research, some studies used buses as probes to characterize and evaluate arterial performance. Tantiyanugulchai and Bertini (2003) used information of one corridor from both AVL and GPS data and found that the maximum instantaneous bus speed achieved between stops was the most reliable output to represent general traffic movement (i.e.,non-bus traffic). Pu and Lin (2008a) reviewed five cases of using buses as probes and highlighted the limitations of the methodology in the following situations: the understanding of the bus-car interaction in urban traffic streams, the uncertainty of bus operations, the lack of traffic data and the difficulty of handling and processing massive AVL data. Pu and Lin (2008b) studied a short segment of a bus route to compare the use of archived driven space, AVL (fixed position at certain points along bus routes) and online time-driven data (data provided by a GPS). They concluded that both types of data have a similar capacity to estimate travel time, although time-driven information is able to better describe the bus operation phenomena.Berkow et al. (2007) also discussed the possibility of using buses as probes to evaluate arterial performance.