Dead Meat
The carcass on the shoulder buzzed with flies and other insects feeding on the rotting flesh. The process of decay started the moment the vehicle, probably an SUV or pickup truck by the amount of damage, rammed into it.
Larger critters had already been by, but there was enough intermittent traffic during the day that the real feast would wait until dark.
In a way, we're always rotting, from the moment we're born. It's thanks to the magic of cellular technology we're able to keep regenerating through the decades, sloughing off the dead skin and useless morality as we go.