Interstate I-684 turned into a parking lot for hours Friday afternoon after a tractor-trailer accident just north of the Westchester-Putnam county line.

According to police, a truck was parked on the side of the road waiting for a tow when a tractor-trailer apparently lost control and clipped the stopped vehicle. Police say the truck went careening off the interstate and down an embankment. The 39-year-old truck driver was flown by helicopter to the Westchester Medical Center with head injuries.

The truck?s smashed front end sat in a small stream that empties into a New York City reservoir south of Brewster. Hazmat crews from Putnam County and the New York City Department of Environmental Protection moved in to contain about 50 gallons of fuel from a ruptured tank on the truck.

Troopers are investigating the accident and are waiting to speak with the truck driver.