With its frequent traffic jams, confusing signs, and occasional chunks of falling concrete, the Brooklyn-Queens Expressway has long been a traffic nightmare. But even transportation experts underestimated the impact that continuing rehabilitation of the road would have on driver safety. Motorists have slammed into protective barriers almost 200 times since a $252 million construction project at the main approach to La Guardia Airport began four years ago, according to documents obtained by The New York Sun.

Between August 2000 and August 2003, vehicles hit the barriers that split a westbound lane in front of the Bulova Avenue bridge 50 times, according to the documents. Elsewhere, motorists took out more than 120 sand filled barrier tubs situated throughout the project, which runs from Broadway to 25th Avenue in Astoria, near the Queens terminus of the expressway.

The state Department of Transportation has touted the construction project as the most costly it has undertaken. It involves reconstruction of 16 bridges, landscaping adjacent streets, and raising CSX freight rail tracks. All of the work must be done while the BQE, which is one of New York City’s – and the country’s – most overcrowded roadways, remains open to traffic. Work began in 2000 and, with completion now scheduled for this spring, has run at least six months behind schedule. The project also is at least 17 percent over budget.

Officials at the state DOT and city police said they could not estimate damages or injuries sustained by motorists in the accidents at the barriers. The New York City Law Department was unaware of any related litigation filed against the city. Construction officials labeled most of the crashes “hit and run.”

Nevertheless, the project’s main contractor, Slattery Skanska Inc., has had to order an additional 50 crash-absorption devices, known as “crash impact attenuators,” which cost nearly $9,000 apiece, and more than 140 sand-filled barrels, which cost about $120 each, to replace those destroyed by accidents, change-order documents show. Each time it replaced an attenuator, Skanska charged the state about $4,000 for a markup on materials and for the cost of labor and overhead. It charged an additional $39 each time it replaced a sand filled tub. Further, the contractor received permission from the state agency to hire tow trucks to stand by in case of accidents or other obstructions in stretches of the construction area that merge into single lanes.

That would bring the cost of dealing with accidents at the barriers to $700,000 or more.

Construction workers at the site say the force necessary to put an impact attenuator out of service would almost certainly do significant damage to the vehicle that hit it. At least one accident, which included a semi truck, tied up traffic for hours.

“This is not going to let up anytime soon,” the executive director of the traffic safety group Transportation Alternatives, Paul White, said. “The city is too reluctant to reduce speed limits, because the BQE is already maxed out at peak hours and even a small change would lead to major backups. It’s an inherently dangerous situation.”

State officials acknowledged the danger but said drivers need to be more careful.

“The problem is that people are not paying attention when they drive,” a spokeswoman for the DOT, Jennifer Post, told the Sun last week. “They are driving too aggressively through work zones.”

Near Albany, an errant driver killed a worker this year, and Ms. Post said cracking down on aggressive driving is a priority of the state agency, which has launched a series of initiatives aimed at getting traffic in construction zones under control. Nationwide, about 1,000 people a year die in construction zones, 85 percent of them drivers and passengers, according to the state DOT. State regulations now require workers to employ traffic-safety officers in construction zones, and fines for speeding in construction zones have been doubled. Along the BQE, the state has spent more than $2 million on traffic-enforcement agents since the start of the project.

Officials at Skanska declined comment on the BQE situation, referring questions to the state agency. But some of the construction workers were willing to speak, as long as their names weren’t used. Most of the accidents have occurred in areas where lanes merge, or single lanes are split into two by barriers, they say, and have resulted from “sheer stupidity.”

“If you tell people to go in one direction they can handle it, but when you tell them they can go one way or the other,” one worker said, shrugging, “they can’t make a decision, so they crash right into the middle. That’s just the way people are.”

Transportation experts expressed surprise at the number of incidents on the roadway, though some said the situation was unavoidable, given the hundreds of thousands of cars that navigate the BQE every day.

“We think that the state DoT is actually doing the best they can under difficult circumstances, and they’re keeping the highway open while they are rebuilding it,” a staff analyst at the Tri-State Transportation Campaign, Michelle Ernst, said. “People just have to take it easy in this construction zone and drive a little slower and be more cautious.”

A spokesman for the American Automobile Association in New York, Justin McNaull, offered a different perspective. “In a situation where there are that many collisions, it’s not enough to just blame the drivers,” he said yesterday. “Transportation officials should do something, such as place more prominent signage, especially if it’s happening in an area where construction is going on.”

Wherever the responsibility lies, evidence of driver mishaps on the BQE is easy to find. On a tour through the construction zone one day last week, the Sun encountered almost a dozen overturned or crushed orange cones – including one lying in the middle of the road beneath an underpass. Strips of shredded yellow sand barrels lay by the side of the traffic-clogged road, amidst plastic bags, discarded yellow police tape, and rusting hubcaps. Many of the newly installed concrete barriers lining the roadway were marred by black smudge marks – telltale signs of errant drivers who strayed off the central road, and probably dented their fenders.