The National Transit Institute, a federally funded training and research organization at Rutgers University in New Brunswick, N.J., has studied the new technologies, but Christopher A. Kozub, the associate director for safety and security programs, cautioned that few have been proved to be fail-safe.
''The application of smart technology is only in its embryonic stages,'' he said. ''The potential is there, but variables like temperature conditions, the passenger environment and rush-hour influxes are all very hard to program into these systems.''
Mr. Hull and Mr. Kozub said that no one has rigorously studied the use of cameras by transit agencies across the world. In the United States, transit agencies vary widely in their use of cameras. In San Francisco, the Bay Area Rapid Transit, which opened in 1972, has cameras in all 43 stations, but the system has its limits. Station agents on duty are responsible for monitoring the video screens for their stations, and only some of the stations record and save images.
In the past decade, vandalism plummeted after cameras were installed in many of BART's 669 cars. ''We want to enhance them to be all digital, with wireless capability, but we're not there yet,'' said the agency's police chief, Gary Gee, who added that upgrading surveillance systems is a major part of the $200 million antiterror wish list that the agency compiled after Sept. 11.
New Jersey Transit, the largest statewide transit agency in the country, uses more than 1,400 cameras across its 11 commuter rail lines, 3 light-rail lines and 240 bus routes. The agency has begun connecting its cameras to computers that can automatically detect suspicious activity, using a complex algorithm.
''Any abnormality that differentiates from the algorithm will set off an alarm or a pager, or give a call to whoever is responsible for that camera,'' said the agency's police chief, Joseph C. Bober.
The system can also be used to avoid the cautionary evacuations that have become the norm since Sept. 11. One day last summer, for example, when a suspicious bag was identified at Pennsylvania Station in New York, the agency quickly reviewed recorded images and determined that it had inadvertently been left behind by an employee.
In Houston, the Metropolitan Transit Authority of Harris County, Tex., opened a 7.5-mile light-rail line, its first, in January 2004. All 17 stations and 18 cars were equipped with cameras, but the agency is now testing enhancements that would allow the cameras to transmit live images wirelessly to police cruisers and law enforcement centers.
In New York City there are 2,328 cameras in 276 stations, but none on the 6,182 subway cars, although the newest ones were built to accommodate them.