I do not have an answer for that, but every year I see turtles that have been hit by cars (five since this spring).
I personally have assisted several turtles in their highway crossing. The area where I notice them crossing is near the Idaho Club golf course and the Pack River Bridge on Hwy. 200 heading to Hope, Idaho.
I spoke to Susan Kiebert who used to be with the Idaho Transportation Department in the spring of 2015. I was hoping she could help me in the process for obtaining a sign that might make drivers aware that those rounded dark objects on the highway are turtles! She said she experienced the same sight of dead turtles on a Clark Fork River bridge crossing as well. She thought the idea of having a warning sign for drivers had merit.
She guided me to Ryan Hawkins and Stephanie Hale of the ITD. They were receptive to the idea and included Idaho Fish and Game in the process by having them research the need for such a sign. After their research they agreed to work out a hinged sign that can be opened when it is turtle crossing season (spring, summer and fall) and closed during the winter.
I am happy to report that yesterday, July 20, the sign is up!
Thank you to all of the people that were involved with this project. It is my hope that with awareness of their presence people will be on the lookout and slow down for them.