A crash Tuesday on the Garden State Parkway has raised questions about why none of the developmentally disabled passengers was wearing a safety belt — and has revived a debate about the safety of passenger vans.

Only the driver, Ahmed Ashour, 22, and the front-seat passenger, Michael Votta, 49, were wearing safety belts, police said Wednesday. They were the only two of the nine occupants who weren't ejected from the van as it skidded off the roadway and flipped over onto the grassy shoulder near Exit 153 in Clifton.

The seven other occupants — four developmentally disabled men and three staff workers — were thrown from the van. At least three were critically injured, and all remained in area hospitals Wednesday.

The group had been on a fishing trip to Sandy Hook and was on its way back to the North Jersey Developmental Center in Totowa when the van crashed.

Mary Helen Cervantes, a spokeswoman for the state Department of Human Services, said the accident prompted a review of policies on the transport of mentally disabled residents. She said the current policy doesn't require staffers to ensure that passengers behind the front seat wear safety belts if they are ambulatory.

That policy requires only that wheelchair-bound clients be firmly secured with wheel locks.

"Clearly, that policy is not strong enough," Cervantes said.

Investigators hadn't determined what made the 15-passenger, 2000 Ford van suddenly veer off the roadway around 3:15 p.m. Tuesday. But federal safety experts have long warned that 15-passenger vans can be hard to handle.

A study by the National Highway Traffic Safety Administration found that passenger vans were involved in more than 1,000 fatal accidents from 1990 to 2002, and that 80 percent of the people who died weren't wearing seatbelts.

"People drive these vehicles like they're cars, but they really should think of them as trucks," said Rae Tyson, a spokesman for the National Highway Traffic Safety Administration. "Any vehicle with that high a center of gravity is prone to roll over under certain conditions."

Tyson said passenger vans are safe if the driver is properly trained and the tires are properly inflated.

But Jeff Wigington, a Texas attorney who has handled a dozen lawsuits on behalf of families who lost relatives in van crashes, says the vehicles aren't wide enough to be stable. Wigington says the 1970s designs used by GM and Ford weren't intended for passengers.

"These vans started out as cargo vans, and the manufacturers simply added seats and turned them into people carriers," Wigington said. "When they did that, they drastically raised the center of gravity upward and rearward, and that makes them hard to handle."

The Ford Motor Co. maintains that the passenger vans are safe if properly operated.

"There are a lot of factors to consider in any accident," said Daniel Jarvis, a Ford spokesman. "We can't comment on the accident [on the parkway] because we simply don't know what happened."

New Jersey's public and private schools no longer use passenger vans, but other state agencies — including the Department of Human Services — still do.

Cervantes said a federal ban only applies to the purchase of new vans.

"The law doesn't require the old vans to be taken out of service," Cervantes said.

The North Jersey Developmental Center declined to name the four developmentally disabled men who were injured in the accident, but it did release the names of the injured staff members:

Ashour was being treated in Hackensack University Medical Center for internal injuries. His condition was not released.

Votta, 49, of Hackettstown was treated for lacerations at St. Joseph Regional Medical Center in Paterson. His condition was not released.

Carol Hungo, 50, of Sparta, was in critical condition with internal injuries at St. Joseph's.

Lois Conely-McGovern, 52, of North Arlington was treated for a pelvic fracture at St. Joseph's. Her condition was not released.

Andrew Vandepolder had a leg injury and was at University Hospital in Newark. His condition was not released.

Among the clients, an 18-year-old man was in critical condition with head trauma at St. Joseph's, a spokeswoman said.

And a 17-year-old boy was in critical condition at University Hospital in Newark, where he, too, was being treated for head trauma.

Two 19-year-old men were in Hackensack University Medical Center with head and facial injuries.