While flipping the bird did not help, don't beat yourself up about it too much. This driver was already endangering your life and out to f**k with you.

Spend some time in the car in that area and find this kid. Don't let it go and do everything you can to get the investigating officer onto him. It's a unique vehicle and should be easy to spot again. If you do find him and he still lives at home (probably not many 20-somethings driving around in a range rover, paying all their own bills), knock on the door and talk to a parent about his actions towards you.