A limousine carrying four sisters, other relatives and friends to a birthday celebration blew through a stop sign and slammed into a parked SUV outside a store in upstate New York, killing all 18 people in the limo and two pedestrians, officials and victims’ relatives said Sunday.

The weekend crash was characterized by authorities as the deadliest U.S. transportation accident in nearly a decade. The crash turned a relaxed Saturday afternoon to horror at a rural spot popular with tourists viewing the region’s fall foliage. Relatives said the limousine was carrying the sisters and their friends to a 30th birthday celebration for the youngest.

The 2001 Ford Excursion limousine was traveling southwest on Route 30 in Schoharie, NY, about 170 miles north of New York City, when it failed to stop at 2 p.m. Saturday at a T-junction with state Route 30A, State Police First Deputy Superintendent Christopher Fiore said at a news conference.

It went across the road and hit an unoccupied SUV parked at the Apple Barrel Country Store, killing the limousine driver, the 17 passengers, and two people outside the vehicle.

Fiore didn’t comment on the limo’s speed, or whether the limo occupants were wearing seat belts. Authorities didn’t release the names of the victims or speculate on what caused the limo to run the stop sign.

It’s the deadliest transportation accident since February 2009, when Colgan Air Flight 3407 crashed near Buffalo, New York, killing 50 people.

The National Transportation Safety Board is investigating.