A lot.
The most dangerous thing about cars is the massive amounts of momentum, inertia and potential energy that can be generated at speed, energy which can cause the car (or anything falling off or released from the car) to have a lot more destructive power than it's weight alone (they say that in an accident, an average passenger in the back seat can hit the person in front with the force of a baby elephant if they're not wearing a seatbelt).
One of the worst automotive accidents in history, the 1955 Le Mans disaster [http://en.wikipedia.org/wiki/1955_Le_Mans_disaster], caused 84 fatalities and 120 injuries, because a car disintegrated at 150mph and individual parts ripped through the massed spectators like grapeshot from a cannon.
Once a car gain enough speed and momentum, it has the potential to be more destructive than a gun or a bomb, depending on what it hits.
Fortunately, most cars don't travel fast enough or hit groups of people to cause such high fatalities and most pedestrianised areas where people congregate have barriers and obstacles which will stop cars, so the majority of car journeys end without incident, but still the potential is there, just like a aeroplane has the potential to wipe out a village if it falls on it from the sky.