Just before the blue car driven by Mary Barnes is hit, the Monte Carlo that hits her already has a dent on its side, indicating they used a previously damaged car for the accident.
The ambulances shown have "Ambulance" on the front. In the real world, ambulances typically have it written in reverse, so that people can read it correctly in their rear-view mirrors.
When Holmes, the ambulance driver, is being chased in his own car, there is an accident where a car rides up on another. Before it happens, the ramp on the back of the front car is visible.