The crippling of the A and C subway lines following Sunday’s Chambers Street station fire provided a dramatic reminder that New York’s subway equipment lags far behind that of other American cities.

The technology in New York’s signaling infrastructure predates the system itself, which began operation in 1904. In contrast, two of the country’s other large subway systems – the Washington Metro and the Bay Area Rapid Transit system in the San Francisco area – have fully computerized control systems, known as automated train control.

Under that type of operation, according to the chief engineer of the Department of Operations for the Washington Metro, Patrick Porzillo, computerized code is transmitted to subway trains through either modules along the running rail or wireless radio-wave technology. Contained in the code is information telling the train what speed limit it should obey, where it should stop and when it should stop, and controlling the opening and closing of subway doors.

At a central control room, supervisors can monitor the entire system on computer screens. Automated train control also allows for broken-rail detection, makes subway operation less vulnerable to snow and ice, allows for track notices announcing the wait time for the next train, and ultimately means the train essentially drives itself.

The Washington Metro, which has a daily ridership of 650,000 and covers 106 miles of track, began service in 1976 and had computerized automated train control from the start.

So did San Francisco’s BART system, which began service in 1972. It has an average weekday ridership of 310,000 and covers 104 miles of track, a spokesman for the transit system, Jim Allison, said.

One of the main benefits of automated train control is that it allows for trains to run more frequently.

Most subway systems around the world used fixed-block technology, the patent for which dates back to 1872, according to the president of Transportation Systems Design, Thomas Sullivan. The Oakland, Calif.-based firm does train technology consulting. In a fixed-block system, no two trains are allowed to be in the same block – a section of track 400 to 1,000 feet long – at the same time.

In a system like New York’s, Mr. Sullivan said, it is impossible to know where a train is within a block. For that reason, a subway train cannot enter a block until the train before it has exited completely. Mechanical trips will stop the train if it runs a red light.

The director of subway operation and rail vehicle engineering for the Massachusetts Bay Transportation Authority, Jeffrey Parker, said the older systems also do not allow for varying train speeds. For example, he said, if a train is traveling at 40 miles per hour in a previous block, it may be safe for the train behind it to follow at 20 miles per hour. In a noncomputerized system, trains can travel only at a predetermined speed – which means that if they can’t travel into the next block at 40 miles per hour, they aren’t allowed to enter into the block at all, he said.

That makes for a lower frequency of trains. Mr. Allison said that at peak rush hour, BART trains run every 135 seconds. Rush-hour frequency on Washington’s Red Line – its most heavily used – is two-and-a-half minutes, a spokeswoman for the Washington Metro, Cathy Asato, said. In contrast, under normal circumstances, the peak frequency of New York City’s A train is every 6 to 8 minutes.

Another advantage of having computerized, updated technology is greater ease in responding to subway disasters – or avoiding them entirely.

Mr. Allison said the last major subway incident to afflict BART was in 1979, when a train caught fire in a tunnel and closed the tube for 12 weeks, prompting a major fire-safety overhaul that included the refurbishing of every BART train car with fire-resistant material. During the 1989 earthquake that left parts of the Bay Area in ruins – it even caused a postponement of the start of baseball’s World Series – BART experienced no shutdowns in service, Mr. Allison said.

Last July, at the Washington Metro’s stop in Silver Springs, Md., a misfortune similar to that afflicting the A and C lines befell the Red Line.

A room containing relays, switches, and other controls was flooded, and the room and its equipment had to be gutted entirely before it could be restored. But service was never suspended on the Red Line, and while train frequency slowed as the line reverted to manual operation, full service was restored within two weeks, Ms. Asato said.

Officials of New York City Transit have estimated that it will take six to nine months to restore normal service to the A and C lines, revised from their initial projection of three to five years.

While no subway system in America is fully computerized that was not computerized when it began service, Boston’s T system – which, having started service in 1897, is older than New York’s subway – has computerized all of its Red Line and part of its Orange Line, bringing to Boston commuters many of the advantages enjoyed by their counterparts in Washington and the Bay Area, Mr. Parker said.

Although Boston, the Bay Area, and Washington have partially or fully computerized, centralized control systems, they do not have the “next generation” of computer technology, Mr. Sullivan said. That is communications-based train control, which the Oakland-based consultant said is already in place at Vancouver and parts of San Francisco.

CBTC, as it is called, eliminates the block-and-relay system entirely, and it allows the position and speed of a train to be known with precision on a constant basis, not only when a train is entering or exiting a block. In San Francisco, the CBTC system allowed for an increase in train frequency to 48 trains an hour from 20 trains an hour. The line now has a maximum capacity of 60 trains an hour, Mr. Sullivan said.

New York, Mr. Sullivan said, is more advanced than most systems in the country in installing CBTC technology, at least in part. The JFK air train already uses CBTC technology, and the $288 million L line project, scheduled to be ready this summer, will be the first segment of the New York subway to move to this next-generation system.

Mr. Sullivan, who was director of new technology train control with New York City Transit in the early 1990s, when the decision was made to move over to CBTC technology, said New York will require between 20 and 30 years to upgrade all its 722 miles of track.

One reason it will take decades is resistance from labor unions, which have protested the safety of the new L line and have objected to job losses stemming from the improved technology, Mr. Sullivan said.

Another factor prolonging the New York system’s upgrade to CBTC technology is that it runs 24 hours a day, while most other systems around the world close for a few hours in the early morning, Mr. Sullivan said.

Yet another complication is the fact that the L-line technology was provided by Siemens, and, because the city wants to have competitive bidding for the retrofitting of the rest of the system. Siemens must reveal information about its technology to other companies, so that they can come up with systems compatible with the Siemens product used along the L line.

Still, Mr. Sullivan said, New York will not take longer than other comparable world systems looking to shift to CBTC technology, including Paris, London, Madrid, Toronto, Singapore, and Hong Kong.