Surprising New Yorkers who had steeled themselves for months of commuting hell, the Metropolitan Transportation Authority announced yesterday that service on the partly disabled A and entirely crippled C lines would be restored today.

Effective at 5 a.m., the C line will be back in commission and A trains will run more frequently, restoring about 70% of the service offered before the fire at the Chambers Street station that destroyed a relay room and vital signaling equipment. V trains, which had replaced C trains in Brooklyn, will return to their normal route.

Previous MTA estimates had put the time for restoration of service to the C line, and complete restoration of the scaled-back A service, at six to nine months, and immediately after the fire the estimated period of disruption was as long as five years.

According to an MTA update, off-peak service on both lines would be normal starting today but “full rush hour service is still a few months away,” so “customers should continue to expect delays and crowding.” The announcement says it will still take six months to restore service completely.

Despite the unexpected good news about train service, there is no similarly rosy improvement in the anticipated cost of the January 23 fire: The estimate of $50 million to $60 million for repairs to the relay room remains unaffected by restoration of the A and C lines, a spokesman for the MTA’s New York City Transit, Mark Groce, said yesterday.

The estimated time requirement for complete refurbishment of the destroyed relay room – which the MTA has announced will take three to five years – will also remain unaffected by the restoration of train service, Mr. Groce said.

Yesterday, the New York City Transit president, Lawrence Reuter, said: “The engineers in the field figured out how to get the system to this level of service,” by bringing in parts from other parts of the subway network, according to the Associated Press.

Mr. Groce said the fix was a patchwork procedure, connecting two otherwise functioning stretches of C-line track that had been served by other lines during the post-fire shutdown.

In Brooklyn, Mr. Groce said, the signaling system was usable, which was why the MTA was able to run V trains along the C track. In Manhattan, north of the Chambers Street station and the stretch of track signals disabled by the fire there, other trains serviced C customers. The B and D lines run along the same track as the C on the Upper West Side, and farther south the 1, 2, 3, and 9 lines are a few blocks from C stations.

Mr. Groce said that while the B and D trains could be operated on the C track north of the affected area, and the V line south of it, the C line had to be stopped because it could not bridge the gap between the two functioning sections of track.

The MTA engineers, he said, have now found a way to do that, which is why C service will resume tomorrow.

As for the A train, Mr. Groce said, a complete service shutdown was avoided by using manual signaling along the affected area of track. With manual signaling, however, it is more difficult to keep trains at a safe distance from one another – previously the task of the destroyed equipment – so the MTA scaled back the number of trains, to avoid straining manual-signaling resources, according to Mr. Groce.

An expert in train-signaling technology, Thomas Sullivan, also said manual signaling is more dangerous than using standard equipment.

He said New York’s subway system sometimes uses manual signaling late at night in the course of conducting routine maintenance. Men and women with flags signal train operators through a section of track, in a practice Mr. Sullivan – who is also the president of the Oakland, Calif.-based train-technology consulting firm Transportation Systems Design – noted was “labor intensive” and said creates a higher “potential for making errors.”

Mr. Sullivan said that New York’s subway system has many rarely used track switches – “there are a lot of ways to get from one track to another that are only used in an emergency or during non-regular operations,” he said – and that these nonessential switches were probably diverted to the stretch of disabled C- and A-line track.

Despite its A- and C-line engineering successes, the MTA faced more mechanical problems yesterday, when a smoke condition disrupted the D line for an hour at midday, according to the Associated Press, which reported that the incident shut service in both directions between 36th Street and Stillwell Avenue in Brooklyn.

Neither did the MTA’s public-relations problems disappear, as many rush-hour commuters late yesterday remained unimpressed with the agency’s work and with its continually revised estimates.

Some were hearing about the service restoration for the first time. At the Chambers Street station where the trouble began, no flyers announcing the service update were posted, and requests to a booth attendant for the latest service information yielded the old flyer about the prolonged suspension of the C line.

At the Jay Street station in Brooklyn, updated flyers – which a worker said were delivered at 4 p.m. – were posted amid the outdated ones. The whiteboard in the station attendant’s booth still announced a suspended C line and reduced A-line service. An MTA employee reacted to the latest news with a jubilant “We work fast! First, three to five years; then, three to five days.”

Less enthusiastic was Williamsburg resident Jake Woland. “I am getting used to the MTA setting low expectations for us. We are expecting a fare hike and all kinds of bad news. This is no different,” he said while waiting for an A train at Chambers Street.

“They change their minds so frequently… they might need a tickertape so we can get a minute-to-minute update,” Mr. Woland said, adding: “I wish there was some kind of outside accountability.”