A slip of two right wheels onto the shoulder of a road and into a guardrail apparently caused a van to plunge into an Eastern Shore creek Sunday, killing a Montgomery County woman and five of her six children as they returned from a beach vacation, Maryland State Police said yesterday.

Meanwhile the sole survivor of the crash, a family friend, remained in satisfactory condition in an Eastern Shore hospital.

Kimberly Pipari, 16, of Brookeville was hospitalized at Peninsula General Hospital in Salisbury with multiple lacerations and fractures, according to a hospital spokesman.

Kimberly was riding with Carol Holmboe, 42, and five of Holmboe's six childrenwhen the Holmboes' van crashed into a highway guardrail on Rte. 50 in Dorchester County about 4 p.m., and, according to Maryland State Police, "vaulted into a creek" about 30 feet away. Police said the van immediately submerged, trapping the occupants. It took about 25 minutes before rescue workers could free the victims from the van, which sank in 8-to-10 feet of water, according to police.

Maryland State Police Sgt. Richard McGee said the metal guardrail was angled up from the road, which apparently allowed the van to arc off the roadway. McGee said police will "look into the design" of the rail. He added that there was no evidence of alcohol or excessive speed. "If they were going 50 miles per hour it should not have occurred," he said.

The accident happened about 50 miles southeast of the Chesapeake Bay Bridge, police said, where Rte. 50 narrows to two lanes and crosses Bridge Creek, which flows into the Nanticoke River.

Neighbors near the family's home at 3616 Patrick Henry Dr., said the family was returning from their cottage at Millville, Del., near Bethany Beach. Holmboe's 18-year-old son, Mark, apparently was driving the van, police said.

In addition to Mark, the other Holmboe children killed were identified as Leigh Megan, 14; Jamie Elizabeth, 12; Scott, 8, and Ryan, 3.

Pipari was rescued by a passerby after being ejected from the van as it hit the water.

Neighbors said the father of the family, Ernest Holmboe, is an assistant vice president at Pacific Sierra Research Corp. After being notified of the accident Sunday, they said, he went to inform the couple's surviving child, Keri, 19, a sophomore at Pennsylvania State University at Altoona.