The Transportation Operations Coordinating Committee's System for Managing Incidents and Traffic (TRANSMIT) is an operational test that uses vehicles equipped with tags of the E-ZPass electronic toll collection system as traffic probes for traffic surveillance and incident detection. The TRANSMIT incident detection algorithm is based on statistical comparison of real-time estimates of travel times with continuously updated historical travel times for the same time period of the day and type of day (weekday, Saturday, Sunday, or holiday). The probability of detecting an incident and the false-alarm rates produced by TRANSMIT during a 4-month evaluation period (January to April 1996) may be considered excellent for the data collected on the New York State Thruway and satisfactory for the data collected on the Garden State Parkway. The mean time to detection of an incident was not estimated at this stage of the evaluation. The TRANSMIT communication system exhibited excellent performance in terms of the transmission rates systemwide, which were found to be near 100%. Only the radio link at Tappan Zee Bridge exhibited a lower transmission rate. A limited probe vehicle test was conducted to determine the detection rate at individual roadside terminals. The lower detection rates observed were site specific rather than systemwide. The performance of the TRANSMIT incident detection algorithm performed very favorably compared with the performances of the best incident detection algorithms reported in the literature.