A tractor hauling an asphalt grinder rolled off a ferry and plunged into the Long Island Sound after the 100,000-lb. combination broke through three sets of chains, killing the driver.

Witnesses say the trailer's rear axles slid off the deck and pulled the tractor into the water. The boat was a little less than a mile from the dock at Orient Point, NY, near the end of a trip from New London, CT, said Coast Guard spokesman Steve Sapp.

Michael Zuber, a driver for Branford, CT-based Big East Equipment Co., was pronounced dead at a hospital.

Authorities were hesitant to speculate about what they called a freakish accident, but some investigators suggested that the parking brakes on the truck and trailer were somehow disengaged, either through a technical failure or some action by the driver, according to a report in The New York Times.