State police said Tuesday that driver fatigue was the apparent cause of fatal motor vehicle accidents in Casco and Hartford on Monday, bringing the total highway deaths so far to 16 in the first 17 days of the month.

Edward McIlvaine, 28, of Wyndmoor, Pa., was returning from the Phish concert in Vermont on Monday afternoon when his vehicle drifted across the center line of Route 302 in Casco and hit a cement truck, Trooper Adam Fillebrown said.

McIlvaine was pronounced dead at the scene, he said, and three passengers were hospitalized along with the truck driver.

“It appears it was driver fatigue,” Fillebrown said of the cause of the crash, “but it is under investigation.”

Michael McCollister, 17, of Sumner died at 6:35 a.m. Tuesday at Central Maine Medical Center in Lewiston after his car drifted off Route 219 in Hartford late Monday night, went up a 15- to 20-foot embankment and struck two trees, Trooper Dan Hanson said.

Because there were no brake marks, no speed or alcohol involved, no known medical problems and it was on a curve, Hanson said, it appears he “possibly fell asleep at the wheel.”

He said McCollister had just left a birthday party when the accident occurred at 10:19 p.m. on a curve near Pratt Hill Road and Camp Wekeela. The 1995 Oldsmobile Delta 88 registered to a family member “drifted right off the road” on a curve, he said.

The teen was taken by Turner Rescue to the hospital.

At Casco, McIlvaine’s 1987 Toyota 4Runner was headed east toward Windham about 3:35 p.m. when it drifted into the westbound lane into the path of a P&K Sand & Gravel cement mixer from Naples, Fillebrown said. The accident occurred near Sebago Lake State Park Road.

Riding with McIlvaine were Walter Leeman, 29, of Orr’s Island in Harpswell; Alex Stuempfig, 27, Bryn Mawr, Pa.; and Alton Wyman, 19, of Wiscasset, who were all taken to Maine Medical Center in Portland for treatment.

A nursing supervisor said Tuesday night that Leeman was in critical condition and Stuempfig and Wyman were in satisfactory condition.

Cement truck driver Randall Pike, 40, of Raymond, who was listed in serious condition late Monday night, was no longer a patient at the Portland hospital, the supervisor said.

Maine State Police Col. Craig Poulin said August is the deadliest month for automobile accidents. It may be the high volume of traffic and people trying to cram too many activities into waning summer days, he said.

While state police are able to set up along highways to target drunk drivers or speeders, he said, “There’s precious little you can come up with for an enforcement strategy that will keep people awake.”

There were five fatal crashes – in Bingham, Sedgwick, Orland, Vanceboro and Addison – over the last week, in addition to the Casco and Hartford crashes Monday, spokesman Steve McCausland said Tuesday.

The highway death of a Bath woman Tuesday morning, Poulin said, brings the total number of automobile-related fatalities for the month to 16.

“I think it’s going at a pace that could exceed what the norm is,” he said. “It’s certainly troubling to see this many this month.”

McCausland concurred, citing August statistics for the past four years. There were 23 highway deaths in Maine in 2003, 21 in 2002, 26 in 2001, and 20 in 2000.

With 16 deaths in the first 17 days of August, he said Tuesday night, “Obviously, we’re going to be above the average” of the last four years and above the average of 21 deaths in August for the past 10 years, if the present rate continues.

Staff Editor Mary Delamater contributed to this report.