For repair crews on the Cabin John Bridge, life between the fast lanes is not easy.

Day and night, a relentless stream of cars and trucks speeds through the bridge's southbound and northbound decks, confining men, materials and equipment into a center section that is often little wider than two car lengths.

There is also the problem of the Potomac River. A 75-foot drop from the bridge could plunge a man into an 80-foot-deep channel of water that the U.S. Coast Guard considers unnavigable. A net of yellow nylon rope stretches from deck to deck to prevent the worst from happening.

This week the ironworkers have swung into some night action, setting monstrous steel girders, weighing more than 30 tons, on top of concrete piers, shaped like angular hourglasses 50 feet tall.

About 10 men work the 9 p.m.-to-5 a.m. shift. "What it's like? Tough man, tough," said Montia Rice, the project manager for the steel erecting operation. "The weather, traffic. Have you ever worked at 22 below?"

"People have no mercy," added Jim Hall, the project engineer. "They throw stuff at you on Friday nights."

Hall refers to the angry motorists who get caught in one-mile backups on Friday night or in the wee hours of the morning when two or three lanes may be closed.

"I've been called names I never knew existed," confided the grizzled Rice, who has been building bridges for 38 years.

About 60 men work on -- and sometimes beneath -- the Cabin John Bridge. The variety of trades involved in redecking the twin span includes crane operators; pile drivers, who hammer steel beams into the earth to support the bridge at either end; carpenters who build wooden forms for the concrete, and laborers, who set up the barriers, break up the old bridge and lay pipes.

As work progresses, the night crew will increase; by midsummer they will be doing half of the work.