Here is some old footage of the huge Craig Lowndes Crash in 1999. Telemetry later showed he was doing 160km/h at the time. Same would happen to a road car but without a cage, helmet etc etc (this was pre-HANS days). Craig missed out on the next round with all of this safety gear.
All it takes is for a mechanical failure on a road car and the same sort of accident can occur. None of us or our cars are bullet proof.....
Craig Lowndes' massive crash at Calder Park 1999 - YouTube