Investigators said he was part of a large cycling group on South Salem Street headed toward downtown at about 15 to 20 miles per hour.
Rosar decided against following the rest of the riders going back to a bicycle shop and instead went home. He made a left turn onto Apex Peakway.
Chief Jack Lewis said cyclists in front of Rosar made the turn, and he then made the turn that put him directly in the path of a car. Lewis said it appears Rosar looked left and didn't see the car that hit him.
"I think, based on a lot of years of doing this. We believe that the first cyclist clears intersection with no eminent danger," said Lewis. "Rosar approaches, looks at the line of traffic and then looks back left and looked beyond the car that was closest to him. The operator of the motor vehicle was looking ahead with no expectation of someone turning in front of them."
Witnesses told investigators that the position of Rosar's bike when he was hit indicated he was looking left.
Police said the driver of the car will not face charges.
Rosar was a long time Triangle area cycling activist. He was known locally and nationally for his involvement in cycling. He was the director of the North Carolina Active Transportation Alliance and involved in many other bicyclists organizations.