Starting next Friday evening, one lane in each direction of the Jones Falls Expressway near 29th Street will be shut down for up to a month while crews make emergency repairs to clogged and collapsed drainage pipes.
Motorists are being urged to map alternate routes or take light rail until the work is completed.
"The capacity is being significantly reduced, and that means mornings and evenings are going to be dicey," said Frank Murphy, the city deputy transportation director. "But there's certainly enough options."
Alternate routes include Park Heights Avenue, Falls Road, Charles Street, York Road and Loch Raven Boulevard.
Officials said they won't know how long the work will take until they can see the extent of the damage, but initial estimates range from a few weeks to a month.
The JFX handles 6,000 vehicles an hour during peak periods. Losing one lane will drop capacity by at least 2,000 vehicles an hour, depending on the length of the merge area. There may be times when crews will have to close additional lanes to make room for equipment, Murphy said.
The southbound closure will likely begin near Cold Spring Lane to give motorists a chance to merge before the curves adjacent to Druid Hill Park.
Pipe damage was discovered during a routine inspection, and subsequent tests indicated that the integrity of the road structure was being compromised by erosion. Without repairs, a sinkhole would most likely develop, Murphy said.
The JFX, Baltimore's highest-volume road, turned 50 years old in December. Murphy said the road surface is "in pretty good shape," given the daily beating it takes, but the utilities below are aging.
The left lanes in each direction will be closed at 7 p.m. next Friday to give crews space to tear up the median and dig down at least 20 feet to reach the pipes.
"It gets tricky," Murphy said. "We're working in an area that was built up during JFX construction, so some pipes are below the original ground level so it could be as much as 40 feet. When we get down there, we could find some other damage."
To pay for the repairs, money will have to be pulled from other accounts, including this year's little-used snow-removal budget, Murphy said.
The road work will be "inconvenient for sure," said Brian Gobell, a Lutherville resident who works at the architecture firm HCM downtown.
His 12-mile commute generally takes about 35 minutes coming south in the morning and 20 minutes going north in the evenings, and the road work "is certainly going to increase my time both ways," he said.
Doug Hoffman, who lives in Hamilton and jumps on the JFX for a quick ride to his job at Constellation Energy downtown, said he expects the road work will cause major problems. The JFX "is pretty sensitive to tie-ups, so I'd imagine that's going to have a big effect," he said.
Having lived in the city for 20 years, he already has a few alternatives routes in mind, he said.
But the road work will "really throw a monkey wrench" into the commutes of others who rely on the JFX to commute farther north or who don't know alternative routes to take, he said.
Baltimore Sun reporter Kevin Rector contributed to this article.