State police say six people have been killed in traffic crashes since late last Friday night and they plan to beef up enforcement efforts for the upcoming Memorial Day weekend.

Details were not available on the latest fatal crash, which took place Wednesday evening in Topsham.

Earlier Wednesday, on Route 9 in Clifton in Hancock County, troopers said 22-year-old Adam Carlisle of Brewer was killed when his car overturned. Investigators say speed was the main cause of the crash. They said Carlisle had passed a tractor trailer at a high rate of speed and it was the truck’s driver that found the car overturned a short time later.

The crash took place about 2:45 a.m. Carlisle was killed instantly and his passenger, 20-year-old Nicholas Muncey of Aurora, was taken to Eastern Maine Medical Center with non life-threatening injuries, police said.

On the opposite side of the state, an 18-year-old driver is in critical condition after his vehicle overturned on Route 202 in Lebanon early Wednesday morning.

State police said Tejay A. Smith, 18, from Lebanon is being treated at Frisbee Hospital in Rochester, N.H. Troopers said the crash took place about 3:15 a.m. and Smith was alone. The York Sheriff’s Department and Sanford police assisted with the investigation. Troopers said the cause of Lebanon crash remains under investigation.

The chief of the Maine State Police, Colonel Craig A. Poulin, said troopers have additional patrols and several special enforcement efforts under way for the holiday weekend. Poulin said extra troopers will be looking for drunk and aggressive drivers, speeders and enforcing Maine’s seat belt and child safety seat laws.

“Memorial Day weekend sets the tone for the summer driving season and the state police’s goal is to make it a safe one,” Poulin said. “Drivers need to take personal responsibility by driving the speed limit, avoid drinking and driving and using their safety belts.”

Poulin said one person was killed on a Maine road last Memorial Day weekend. Maine had fatality-free holidays in 2004 and 2003.

Among those killed since Friday night, are a 42-year-old man who died in a one-car crash in Industry late Friday, two teenage boys who died in a one-car crash in Belgrade early Saturday morning and a 39-year-old New Hampshire man who died in a two-car crash on Route 1 in Woolwich Sunday morning.