These shots are done by using a "rig" which mounts the camera to the car then the car is driven while the shutter is opened for a slightly extended time.

Rigs are a very well kept secret among auto photographers but can be built with some research and patience, or they can be bought for a very steep price. The rigs actually end up being in the shots and are later photoshopped out of the image (yes it is common practice ask around if you like).

I know people who have spent as little as $50 building rigs and spent as much as $1200 building or buying a rig.