I would implement the following :
Vehicles with Petrol / Diesel (you also have to fill up at filling stations)
Speedometer / Revometer
Sell vehicles to other online players on a web site that you could advertise your vehicle on.
Police doing a checkpoint for road tax and insurance and licence.
police doing a speed check for speeding
if your caught for an offence by the police you should have to go to court and face the judge and see what sentence you should be given..... you could then try to escape (Like BUST OUT)
your friends from your crew could try and help you break out of prison and taking to a hideout but others could inform police to your whereabouts for a reward if your found.
the game should be set in real time to get from A to B.