SCHOHARIE, N.Y. — A limousine loaded with revelers bound for a 30th birthday celebration blew through a stop sign at the end of a highway and slammed into a parked SUV outside a store, killing all 18 people in the limo and two pedestrians in the deadliest U.S. transportation accident in nearly a decade, officials and victims’ relatives said Sunday.

The collision turned a relaxed Saturday afternoon into chaos at an upstate New York spot popular with tourists taking in the fall foliage. Relatives said the limousine was carrying four sisters and their friends to a birthday celebration for the youngest.

“They did the responsible thing getting a limo so they wouldn’t have to drive anywhere,” their aunt, Barbara Douglas, told reporters Sunday. She said three of the sisters were with their husbands and identified them as Amy and Axel Steenburg, Abigail and Adam Jackson, Mary and Rob Dyson and Allison King.

Douglas said the couples had several children among them who were left at home.

“They were wonderful girls,” Douglas said. “They’d do anything for you and they were very close to each other and they loved their family.”

The 2001 Ford Excursion limousine was traveling southwest on Route 30 in Schoharie, 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, police said.

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.

The crash “sounded like an explosion,” said Linda Riley, of nearby Schenectady, who was on a shopping trip with her sisters. She had been in another car parked at the store, saw a body on the ground and heard people start screaming.

The store manager, Jessica Kirby, told The New York Times the limo was coming down a hill at “probably over 60 mph.” In an email to The Associated Press, she complained that the junction where the crashed occurred is accident-prone.

“We have had 3 tractor-trailer type trucks run through the stop through our driveway and into a field behind the business,” Kirby wrote. “All of these occurred during business hours and could’ve killed someone then.”

The National Transportation Safety Board is investigating.

Police didn’t comment on speed or whether the occupants of the vehicle had been wearing seat belts.

The vehicle was an after-market stretch limousine, according to an official briefed on the matter who was not authorized to discuss an ongoing investigation publicly.

Safety issues on such vehicles have arisen before, most notably after a wreck on Long Island in July 2015 in which four women on a winery tour were killed.