Though the 18-year-old Stamford youth severely injured in a four-vehicle collision in New Canaan last Thursday remains in critical condition, he is stable and "showing improvement," police said Tuesday afternoon.

The teen is at Yale-New Haven Hospital, where he's being treated for injuries he suffered what an official called "a high-speed" accident that sent three others to the hospital.

The drivers of the three other vehicles were treated for "non-life-threatening" injuries at Norwalk Hospital, police Sgt. Carol Ogrinc said.

All four drivers were wearing their seatbelts at the time of the accident. Contrary to previous reports, no one was ejected from a car, but two needed to be extricated from their vehicles, Ogrinc said Tuesday.

None of the drivers' names has been released as the crash remains under investigation, but police said the others involved were a 50-year-old New Canaan woman, a 50-year-old Norwalk man and a 41-year-old Wilton woman.

Police on Monday released more details on what Police Chief Leon Krolikowski had called a "complex" collision in the immediate aftermath of the event.

The crash on Silvermine Road, near Clapboard Hill Road, took place shortly after 5:30 p.m. Thursday.

Both the teen and the Wilton driver were traveling east on Silvermine Road, toward New Norwalk Road, while the other two drivers headed west, according to the report.

When officers arrived at the crash scene -- about 375 feet east of Clapboard Hill Road -- the New Canaan woman's vehicle was on its side in the woods on the westbound side of the road, Ogrinc said. Two other vehicles were off the shoulder on the east-bound side with severe damage and a fourth vehicle was stopped on the eastbound lane. All four cars had their air bags deployed.

Fire Chief Jack Hennessey said Friday the four-vehicle collision was "a high-speed accident" and that three of the cars wound up off the road.

Hennessey said it took 35 minutes to extricate a male driver from one vehicle, a small Subaru.

Other vehicles in the collision were a large Audi SUV, a Chevy Tahoe and a BMW. None of the drivers had a passenger, according to police.

The cause of the accident is still being probed, Ogrinc said, but no charges have been filed as yet.