MERRIMACK — Road rage may be to blame for a serious car accident on the F.E. Everett Turnpike Monday that has left a man fighting for his life.

“Yes, there are indications that this was road rage,” said Capt. John LeLacheur of the New Hampshire Department of Safety.

Witnesses told police that an altercation between two motorists began at the Bedford toll plaza and continued south to Exit 11, where the two vehicles collided around 11:20 a.m.The driver of a silver 1999 Isuzu Rodeo reportedly tried to pass a box truck that was in the breakdown lane and either struck or cut off a blue 2008 Chevrolet Aveo, according to police. Ultimately, both vehicles went out of control as they headed southbound just north of the exit 11 off-ramp, police said. The Aveo hit a jersey barrier while the Isuzu rolled over onto its roof.

The driver of the Isuzu, whose name has not been released, was thrown out of the car and suffered “serious, possibly life-threatening injuries,” LeLacheur said. He was taken by helicopter to Beth Israel Deaconess Medical Center in Boston.

Both lanes of the turnpike were closed while the medical helicopter landed on the roadway. For several hours, the southbound lane remained closed while authorities investigated; both lanes were fully opened by 4 p.m.

The driver of the Chevrolet, Gregory Clark, 56, of Northfield, was not injured. There were no passengers in either of the vehicles, authorities said.

“Obviously, this is still under investigation,” said LeLacheur, explaining two independent witnesses had provided thorough statements to police. However, it is still unclear what prompted the road-rage altercation, he said.

LeLacheur said it was fortunate no one else was injured, especially given the high volume of traffic on the turnpike around noon.

“I am glad an innocent body wasn't injured,” he added, reminding people of the serious consequences that can result from road rage. “Unfortunately, these things happen,” he said. ”You get cut off, it happens. People just have to learn to let it go.”

Police said the injured driver's name was being withheld until proper notification can be made to family members.

Photographs taken at the scene by emergency crews show the severely damaged Isuzu rolled onto its roof, with a shoe and other debris lining the roadway.

State police are urging anyone who may have witnessed the accident to call Trooper Kieran Fagan at Troop B, 603-223-4381.