The family of a woman and her adult son killed when a tree along the Garden State Parkway fell onto their car in 2008 can't sue the operator of the toll road, an appeals court ruled Monday.

A three-judge panel ruled that the New Jersey Turnpike Authority, which operates the Parkway, couldn't have known that the 80-foot hickory tree might fall.

Joel Baudouin, 42, of Arlington, Mass., and his mother Marie Vernet, 72, were killed when the tree crashed down on his Volkswagen Passat on Christmas morning in 2008. Baudouin's two daughters, then 13 and 8, were seated in the back and injured.

The four were traveling south near milepost 151.5 in Bloomfield, minutes from arriving in Belleville to spend the holiday with family, when the tree, which was decayed on the inside, tumbled over during winds of about 24 mph.

The Parkway checks trees by the "windshield inspection" method -- a landscape specialist sits in the passenger seat of a truck as it travels slowly along the shoulder of the highway looking for trees that appear dead, near death and in danger of snapping.

The court called the way the Turnpike Authority checks trees, "a sensible approach to monitoring the parkway," adding, "Courts do not have the authority to require that the Turnpike Authority improve or refine its method of inspection."

The tree was about 16-to-18 feet from the guardrail and crushed the front passenger section of the car, which was in the center lane.

The girls' mother, Chantal Baudouin, has already settled lawsuits against Bloomfield and a contractor, Elite Tree Service. The terms of those settlements are not known.

Jeff Goldman may be reached at jeff_goldman@njadvancemedia.com. Follow him on Twitter @JeffSGoldman. Find NJ.com on Facebook.