quote http://www.consolecheatcodes.com/xbox/needforspeedmostwantedcheats.html

Get some cops to chase you, then go to the bus stop. Get on top of the buses and make sure that the front of the car is at the edge of the last bus so that the cops can see you and do not lose you. Keep looking behind you, because the cops will sometimes find a way on top of the buses. When they do get on the buses, just reverse as soon as you see them coming and push them off. Only one cop car will come on top of the bus. Do this for as long as desired. When you want to lose them, just reverse, park in the middle of the buses, and wait until your Cool Down bar fills. The cops will also drive crazy and crash into themselves, giving you extra bounty and bring up your rap sheet rankings on police vehicles immobilized and police vehicles involved.