"Chicken" is also an idiomatic synonym for "frightens easily." They do have some instinct for avoiding danger.

They definitely cross roads.

In the mountains around Trondheim, Norway, you run into free range chicken farms (and sheep roaming the mountain top). Signs warn you that chickens are about and I think them getting hit is a real concern if you are maximizing chicken freedom.

That said, these aren't busy roads. The more traffic, the more barriers to keep the animals from getting hit.

or perhaps it's an artefact of them having a higher contrast against the asphalt and being somewhat fat and puffy compared to most roadkill animals