BOSTON -- State police were investigating Friday a bizarre accident on Route 128 in Westwood that sent a storm drain cover crashing through a man's car windshield, hospitalizing him and backing up traffic in all directions for hours.

The accident occurred around 5:30 a.m. in the northbound lanes of the highway, near the University Avenue exit.

Much of the road was closed while a helicopter was brought in to take Pawel Swierczynski, 39, of North Easton, to Brigham & Women's Hospital, where officials said he was in critical but stable condition.

Three lanes of the highway were closed as a result of the accident for most of the day, and thousands of commuters were backed up in traffic that extended back to Braintree. The highway was not fully reopened until about 7 p.m. on Friday.

"I've been in traffic jams before. This is probably the worst I've ever been in, by far. Easy," one stuck motorist said.

"I didn't think it would be this bad this far back, and then it just got progressively worse," another driver said.

Police said it appeared a tractor-trailer dislodged a metal catch basin cover, which flew into the windshield of a 2003 white Toyota Corolla, which then crashed into a Jersey barrier.

"The highway is dangerous and things do happen here. This is just one of many things that occur here that sometimes motorists can't expect or predict," State Police Lt. Bruce Lint said.

State police responded to a similar call regarding a loose storm grate in the same area on Thursday, but they had little to say about the investigation. MassHighway said it instructed contractor SPS New England to secure all of the grates along the roadway.

"We became aware of storms covers becoming slightly dislodged and some that were rattling in their frames. A couple of days ago, we directed the contractor to secure all 24 catch basin covers that are in that construction zone," MassHighway Commissioner Louisa Paiewonsky said.

The catch basins typically are not in interstate roadways, but the Westwood stretch of the highway has been under construction for some time. The grates are usually found in medians or breakdown lanes.

"We had understood that the (welding) work was completed. Part of the investigation is looking into how this became dislodged after the repairs had been completed by the contractor," Paiewonsky said.

Experts say when a motorist's car is damaged on a state highway they have very little legal recourse. Generally, state law does not provide for state responsibility on a state road. If you get a flat after hitting a pothole, there is no one to call.

But if your car is damaged at a construction site you can take it up with the construction company, which, in most cases, will reimburse you if they're negligent. You may have some recourse if you your car sustains damages on a road owned and maintained by a local municipality. In some cases, they'll reimburse you for repairs, but the state rarely will.