Traffic tie-ups on the Chesapeake Bay Bridge will become significantly worse starting Monday when an additional westbound lane is closed as construction crews rush to fix a botched paving project, Maryland officials announced yesterday.

The center lane closure will reduce the three-lane westbound span to a single lane from 10 a.m. to 5 a.m. the next morning while crews repave the left lane. Two westbound lanes will remain open during the morning rush from 5 to 10 a.m. and on Election Day, Nov. 2.

State officials said they took the drastic step because they are racing against cold weather to repave parts of the westbound span of Route 50 after serious cracks were found in pavement that was laid as part of a four-year construction project.

Officials had hoped to complete the work at night, but they said rain has interrupted workers on six of the 11 nights they have tried to pave. In ideal conditions, workers can lay down about 700 feet of concrete a night; so far, 3,000 of the 12,000 feet have been poured, officials said.

But there has been only one ideal night so far, and officials estimate that they have just a few weeks to find those conditions before temperatures drop below 45 degrees, the cutoff mark for laying the type of concrete they are using. Because the bridge is over water, its temperature tends to be 4 to 8 degrees warmer than on land, officials said. But they also said they can't work when winds exceed 15 mph and when it rains. If the work is not completed before winter temperatures set in, one bridge lane will be closed until spring.

"I apologize for the inconvenience drivers have experienced and what looks like continuing inconvenience," Maryland Transportation Secretary Robert L. Flanagan said at a news conference yesterday. He added that drivers ought to expect "lengthy backups in both directions at any given time."

Flanagan said a single lane can move about 1,400 cars an hour in ideal conditions, which won't be the case on a bridge during a construction project. He said about 1,800 cars try to cross the westbound side of the bridge each hour during the day, so several hundred cars will be stacking up by the hour all day.

"The next few weeks are going to be extremely difficult for all of us who travel the Bay Bridge," he said. "There's no way to sugarcoat the situation."

During particularly bad times, traffic engineers may shift some westbound traffic onto one of the two eastbound lanes, Flanagan said.

He also said that officials would launch a print and radio advertising campaign to alert drivers of the expected delays and asked people to avoid the bridge if possible.

Flanagan reiterated that the cost of the repaving will exceed the $7 million it cost the first time, adding that extra work crews, additional emergency response teams, the advertising campaign and other unusual steps would inflate the costs even more than expected.

Weather and traffic have always been controlling factors in the paving project. State officials avoided paving during summer months, when many construction projects are scheduled, because of the tens of thousands of drivers who head to and from the Delaware, Maryland and Virginia shores.

Instead, officials used a type of cement, called microsilica, that was believed to be easier to pour during cold weather. But it was removed after significant cracking was discovered and is being replaced by a latex-modified concrete that is weather sensitive.

The result for travelers is summertime traffic in the middle of autumn.

In addition to the center lane closure, all westbound lanes are closed from 9 p.m. to 5 a.m. Mondays through Thursdays.

On Fridays, the center lane closes at 8 p.m., and the right lane closes at 9 p.m. The right lane reopens at 7 a.m., and the center lane at 9 a.m. The same is true Saturdays, except the center lane closes at 10 p.m.

On Sundays, the center lane closes at 10 p.m. and the right lane closes at midnight, before both reopen at 5 a.m.

Beginning Monday, westbound travelers on the Bay Bridge will have just one lane -- except during the morning rush.