There is an avulsion fracture of the PCL (type 1) at its insertion on the posterior tibial eminence, most likely secondary to an impact of the tibia on the car's dash. This mechanism makes sense because this fracture involves the non accelerating leg, which is typically flexed in position while driving, creating a good bio-mechanical scenario for shearing the tibia posterior relative to the femur in a frontal impact situation. 

This case is courtesy of Eric White, MD, who generously shared it with me.