Thanks,
Sure there is lots of ways to do it but I render the image with-out any cars first off, then render the image again with cars. Cut the cars out, do the S-curve thing in Photoshop to them so taking the contrast right up. Then blur them as much as you want. Last off apply a fare and change the colour and blur that as well.
Normally have to play around with the shadow and any reflection till it looks right.
Think you can do it in Max using a Vray Physical Camera and then animating the car over a longer exposure but you don't get as much control, and I've heard render times are quite high.
Really it's just playing round till you find something that looks better, I've found that darker cars work better at night.
Hope that helps.