STAMFORD -- A state Department of Transportation review has found that two of the three trees that fell on cars over the past two weeks on the Merritt Parkway -- one killing a Massachusetts driver -- were healthy and the incidents could not have been foreseen.

The health of a third tree that fell, causing a three-car accident in the northbound lanes between exits 42 and 44 in Westport on Sunday night, has not yet been determined.

DOT spokesman Kevin Nursick said the tree that caused the death of Norman Gamache, 74, of Westport, Mass., as he was driving southbound a quarter mile past the Wire Mill Road overpass on the afternoon of June 23, appeared healthy when examined after the accident.

Nursick said the tree, located 20 feet or more from the roadway, had been uprooted during a heavy thundershower just before 1:30 p.m. That tree ended up blocking both southbound lanes and one northbound lane after it fell.

Two other women in the car, one from North Dartmouth, Mass., and the other from Scarsdale, N.Y., were injured in the crash.

Six days later early on June 29, two cars were damaged and one person was injured during another thundershower when a tree fell on the southbound lanes between exits 42 and 44 in Westport.

Nursick said that tree was also deemed healthy when it was examined after it dropped.

Nursick said Thursday that he is waiting to hear about the condition of the tree that fell Sunday night.

The trees that killed Gamache and hit the two cars a week ago Wednesday "would not have been touched by us because they were healthy and not posing a problem," Nursick said.

"Healthy trees can and often do succumb to strong weather events, and the solution to something like that is rather nuclear in that we would have to remove virtually every healthy tree that could potentially fall in the roadway given the right set of circumstances," Nursick said.

He said that the last Merritt Parkway tree that caused a fatal event fell in June 2007, killing two people driving through Westport, and was also deemed healthy. Nursick said that tree, a white pine 65 to 75 feet tall, was growing more than 30 feet away from the roadway when it fell and killed a Pelham, N.Y., couple. Rather than having been uprooted, that tree was sheared from its base, Nursick said.

Much of the danger with trees on the Merritt Parkway has to do with the number of vehicles that use the roadway, Nursick said.

"When a tree falls on a local road or state route, chances are there is not going to be a car there when it happens. When you talk about a tree falling on the Merritt Parkway, chances are more than likely there will be a car where that tree is falling due to the high traffic volumes," he said.

While he said he realizes that it will not offer solace to the friends and family of those who have been killed, Nursick pointed out that it is a very rare occurrence when a tree falls on a moving car.

"It is even rarer if there is not some type of storm event associated with it. Obviously, these are tragic events when folks lose their lives... But it is very rare. We will continue to have a proactive program to maintain trees near roadways throughout the state," Nursick said.

Merritt Parkway Conservancy Executive Director Jill Smyth said that her group supported the DOT's efforts to maintain the trees and enhance the safety of the parkway.

She agreed that removing all possibility of trees falling on the road would ruin the beauty of the 72-year-old parkway.

Nursick said DOT workers will continue to do what they have been doing to care for the trees along the Merritt, which includes "continued vigilance."

He said tree maintenance is a regular activity, akin to mowing grass.

"We remove dead, decaying or compromised trees as needed on all state roads, and we do so on a day-to-day basis," he said. Nursick said healthy trees are also cut down if they are too close to a roadway and pose an impact hazard.

"Sometimes perfectly healthy trees showing no overt signs of weakness break, or fall completely, particularly during storm conditions. Preventing this, despite our best efforts, is virtually impossible," he said.

Staff writer Martin Cassidy contributed to this article.