The cop gave you a load of bull! That's assault with a deadly weapon, at the very least! 4 numbers on a license plate plus the make and model of the vehicle is more than enough for a detective to find a suspect. Hell, give me access to a DMV computer and I could probably do it in a week or two!

I'd re-visit the police, and get a lawyer. People who intentionally endanger people like that on the road probably already have a history, and will most likely perform a similar act on another random victim in the near future. And I say this as a pedestrian, bicyclist, and a motorist!