WINDHAM — A Derry man was critically injured yesterday when he was ejected from his car and landed in the high-speed lane of Interstate 93, according to police, who later tracked down a second driver involved in the crash.

The accident, which occurred shortly before 4:30 p.m. near the weigh station, forced police to close the northbound side of the highway for about 21âÑ2 hours, state police Capt. John LeLacheur said. Traffic was backed up for miles - and hours - as police investigated the crash and sought a second driver who had driven away.

Mario Poto, 38, was taken by Windham Fire Department ambulance to Parkland Medical Center in Derry and then flown by medical helicopter to Brigham and Women's Hospital in Boston. His condition was not available earlier today.

State police initally said they believed a second vehicle was involved in the crash, but could not find the other driver and did not know if the vehicles collided. Shortly before midnight, they announced that the second driver, Charles Hutchins, 49, of Salem, had been found.

The two vehicles were traveling north when Poto suddenly lost control of his car, striking a large rock and trees - ejecting him from the car. The Honda received heavy front-end damage. Hutchins, driving a blue Ford sport utility vehicle, was not injured, police said.

No charges have been filed, police said. Details on how Hutchins was found were still unavailable early this morning.

Police interviewed several motorists who witnessed the crash and pulled over, LeLacheur said.

Motorists were at a standstill for several miles as state police investigated the wreckage. A tarp covered the front of the blue Honda and pieces of the car were strewn across the blood-spattered road. State troopers were still gathering evidence, including vehicle fragments, at the crash scene two hours after the accident occurred as it became dark. At least one fire engine also was sent to the scene.

The northbound side of I-93 was reopened about 7 p.m.

Police closed the northbound side of I-93, between exits 3 and 4, for about 15 minutes after the crash, and diverted northbound traffic off the highway at Exit 3 in Windham.

Traffic on the northbound side of the highway, just south of the accident, was diverted onto the southbound side via an emergency crossover road in the median strip.

Large tractor-trailers, which were too big to use the crossover, were forced to back up, heading south, down the northbound lane to Exit 3, where they got off the highway, LeLacheur said. An empty school bus also had to backtrack to Exit 3 to get off the highway, he said.

Some motorists who were diverted off the highway expressed frustration and said they didn't know what secondary roads to take to get where they were headed, including Bedford and Manchester.

Police contacted Massachusetts authorities, who placed electronic signs along I-93 northbound to alert motorists to the accident in Windham, LeLacheur said.

The New Hampshire Department of Transportation also was involved in handling the traffic.

Four barrels were placed at the I-93 northbound on-ramp on Route 111 in Windham to keep anyone from getting onto the highway. At the same time, all motorists on the northbound side were diverted off the highway at that exit, and police directed the extra heavy traffic.

Motorists were forced to use secondary roads. LeLacheur said he hopes they took advantage of the emergency routes, marked by blue DOT signs, which include Route 28 through Windham and Derry, where traffic was slow moving for a couple of hours.