An 18-year-old man was killed yesterday when his car ran off a rural road in northeastern Maryland and hit a tree, state police reported.

Rodney Todd Helsel of Appleton Road near Elkton was driving near his home when his westbound Volvo S40 ran off Jackson Hall School Road, plowed through a grassy field for about 1,000 feet, flew into the air and hit a tree.

Police said the crash - one of three serious accidents in Cecil County overnight - is believed to have occurred between midnight and 1 a.m., but that the wrecked car was not discovered until about 5:30 a.m.

The accident remained under investigation. Police said that Helsel probably was not wearing a seat belt and that alcohol did not appear to be involved.

About 1:45 a.m., a North East man was injured when his Jeep ran off Maloney Road on the outskirts of Elkton, hit a drainage ditch and flipped over, state police said.

The driver, Keith Doyle, 22, of the 1600 block of Pulaski Highway was reported in serious condition at Maryland Shock Trauma Center in Baltimore.

Late Saturday, a 21-year-old North East man was injured when he was hit by a van while trying to walk across Route 274 south of Calvert, police said.

The victim, Joshua Belcher, was reported in serious condition yesterday at Shock Trauma. Police said the cause of the accident, which occurred about 11:30 p.m., appeared to be pedestrian error.