You can have some fun with that here
http://www.calctool.o.../newtonian/projectile
For example if you assume the bridge is a 30 degree angle and the car hits at 70 mph you'd go 86 meters and a maximum height of 18 meters.
If that seems a lot to you then you're right. Air resistance is neglected and that's quite a big factor in a calculation like this.
It's also fiendishly difficult to account for. A proper scientific answer is related to the Navier Stokes equation - which is still unsolved and has a $1 million bounty on it's head.