An ordinary camera would work if mounted rigidly to the car, you could shoot a video and then take out the center line after the fact. 55 miles/hour is about 80 ft/sec so the horizontal resolution is a little bit more than a foot with a 60 fps video, you could make out houses but not read house numbers.
I think most webcams have a low-level interface that would let you read out part of the display without reading the rest so getting a better frame rate could be done at low cost too.
I think I'm going to try taking pictures of clouds first...