PORTSMOUTH — Samantha Kavanagh, 15, the daughter of former School Committee Vice Chairman Terrence Kavanagh, was in critical condition yesterday in the intensive care unit of Hasbro Children’s Hospital, a day after she was struck by a car as she was running across the four lanes of busy East Main Road.

The car was driven by an off-duty Portsmouth police officer, Mark Mooney, 36, of Tiverton, according to state police Capt. James Swanberg. He declined to release the victim’s name, but Kavanagh was identified by Sylvia Wedge, chairwoman of the Portsmouth School Committee and a Kavanagh family friend.

Tuesday’s incident, at the bottom of Quaker Hill near Brooks Pharmacy, marked the third car-pedestrian accident in the last two years on the same mile-long stretch of East Main Road, where speed has long worried law-enforcement officials.

Swanberg said there was no indication that Mooney exceeded the “normal flow of traffic.”

But he and Portsmouth Police Chief Lance Hebert agreed that the “normal flow” is 10 to 15 mph above the posted limit of 25 mph.

“The flow is 35 to 40 miles an hour — except when I have a police officer there. Then, it’s 25,” Hebert said.

“But that could be said of the entire East Main and West Main roads,” Hebert continued.

“It’s going to take the overall concern, not only of law enforcement, but of the state and towns affected, to be able to come up with reasonable, cost-efficient ways of slowing people down,” he said.

A proposal for a Town Center on Route 138, from Town Hall at the top of Quaker Hill past Tuesday’s accident site to Clement’s Marketplace at the foot of Turnpike Avenue, would have three roundabouts, or rotaries, that would slow traffic, Hebert said. But the plans are in their preliminary stages and actual construction is still years away.

“And that’s only a portion of the road,” he said.

Hebert said Mooney, who was on his way to work at the time of Tuesday’s accident, has been placed on administrative leave to take advantage of a new policy that provides confidential counseling to officers who have experienced traumatic events.

He said Mooney was very shaken by the accident.

The Portsmouth police initially asked the state police to assist with the accident because of its severity and then asked troopers to take over the investigation when they learned the driver was an off-duty officer on their force, Swanberg said.

Mooney’s car has been impounded, which is normal procedure, he said. State police reconstruction of the collision is not yet complete, he said.

On Tuesday, the state police said the right front fender of Mooney’s car struck the victim, the second of two girls who ran across the highway.

Wedge, the School Committee chairwoman, said the first girl, whom Wedge did not identify, had reached the other side of the road before she heard the crash. Wedge said Kavanagh suffered multiple fractures.

Initially taken to Newport Hospital, she was transferred to Hasbro Children’s Hospital, where she underwent emergency surgery, Wedge said.

“We are still on our knees” in prayer, she said.

In September 2005, 64-year-old Jean Correia was killed while crossing the same stretch of East Main Road where Tuesday’s accident occurred. Correia apparently had gone shopping and was on her way home to Quaker Manor, a housing complex for the elderly.

Six months ago, 90-year-old Adelia Payton was struck and killed on the same highway about a mile away, after attending an afternoon Mass at St. Anthony Catholic Church at 2836 East Main Rd.

gmacris@projo.com