Just prior to the BMW crash, it is shown to be driving at a very slow speed (especially compared to the fire department truck), perhaps 10-15 MPH. From a speed of 20 MPH, the car would stop in about 20-30 feet once the brakes were applied. It would not slide the long distance shown and retain enough energy to go through the guard wires on the side of the road.
After the BMW crashes, the fireman uses a cell phone to call in the crash to the station. Since he was in a fire department vehicle, proper procedure is to use the radio in the vehicle to alert dispatch so additional resources (such as EMS and law enforcement) would be sent to him immediately and an incident number could be generated.