This study evaluates the effectiveness of the New Jersey Garden State Parkway (GSP) Alternate Bus Routing (ABR) system, an Advanced Public Transportation System (APTS). The GSP ABR Field Operational Test (FOT), which was conducted on a small portion of the parkway, was mainly concerned with real-time routing of New Jersey Transit (NJT) buses traveling the GSP to a parallel alternate route to avoid congestion on the parkway. One of the most important features of this FOT is the use of NJT buses as probe vehicles that provide real-time travel-time information to the bus routing algorithm. The use of probe vehicles for network surveillance increases the attractiveness of similar systems that can be deployed over larger networks where infrastructure-based surveillance can be prohibitively expensive. The functional evaluation of GSP ABR includes the collection and analysis of data from various sources including traffic sensors, probe vehicles, and surveys conducted among transit bus operators and system users. During the official testing period in 1997, the GSP ABR system produced accurate diversion messages, which proved the reliability of the system. However, the relatively short length of the alternate route, U.S. Route 9, and similar traffic patterns observed on both routes did not give the evaluation team the opportunity to observe scenarios where statistically significant travel-time improvements exist. This result prevented the evaluation team from reaching conclusive recommendations in terms of the effectiveness of this FOT. However, the survey results show that both transit bus operators and ABR system operators believe the system can be very beneficial if implemented in a different network. From a policy point of view, the general conclusions of the functional tests presented along with a list of lessons learned can be used in the effective design of future FOTs in the area of APTS.