DEDHAM — The initial report about the Aug. 5 fatal collision on Route 1A indicates 85-year-old Richard Olson, who was driving to his summer home in Ellsworth, may have drifted in his lane and overcorrected, causing his vehicle to cross the centerline and hit an oncoming truck head-on.

Olson, a former mayor of Des Moines, Iowa, and the occupants of the truck, Phillip Carter, 32, and Roxanne Papken, 25, both of Bangor, all were killed. Investigators, in this early report, so far are unable to pinpoint why Olson may have crossed into the other lane

“There is no evidence of braking from either vehicle,” states the Maine State Police initial crash report, filed by Trooper Gregory Roy. “It is unclear of why (Olson) crossed the centerline.”

Olson had a valid Iowa driver’s license but was required to wear corrective lenses and have left and right outside rear-view mirrors installed on his vehicle, according to Kim Snook, director of the Office of Driver Services for the Iowa Department of Transportation. The extra mirrors help older drivers with reduced peripheral vision, she said.

While it is unclear whether Olson’s age was a contributing factor in the Aug. 5 crash, he was the fifth driver age 65 or older to be involved in a fatal crash in Maine this year, officials say. To date in 2014, 75 people have died in 67 car accidents across the state.

Maine has the fourth-highest share of traffic crash fatalities involving drivers 65 or older in the nation, and the ninth-highest percentage of drivers age 65 or older — nearly 20 percent of the state’s 1 million licensed drivers.

There are 206,228 Mainers age 65 or older who have a driver’s license, according to 2013 Maine Bureau of Motor Vehicles data. Of those, 130,121 are 70 or older.

In Maine, drivers age 65 and older must renew their license every four years instead of six. A vision test is required for those who renew their license after age 40, at every second renewal until age 62, and then at every subsequent renewal, according to the state.

Iowa has graduated driver’s license renewal requirements, according to the state’s Department of Transportation. When Iowans age 69 renew their license, it’s for five years, whill those age 70 get a four-year license, 71-year-olds receive a three-year license, and those age 72 or older are issued a two-year driver’s license.

“Iowa is one of the top four,” said Snook about the percentage of elderly drivers in her state. “We do a lot of restricted licenses. We check peripherals. Other states do not. We actually require them to come in (every two years) so we can see them. Every state deals with issues surrounding (elderly drivers).”

The final report on the Dedham crash is expected to be filed in September and should provide more details, according to Maine Department of Public Safety spokesman Stephen McCausland.

“Because of the magnitude of the crash — the three deaths — it’s going to take a bit longer,” he said.