Somebody just has to stop these Lego people. Now look what they did.
The tractor contains sensors for the steering and drive motors, while the trailer carries the RCX controller and an earthmover. The Truck can back up in a straight line by using the sensors to determine if the trailer is off center, and applying corrective steering in either direction.
It uses MindStorms robotics. This rig even has one of those annoying beeping backup warning devices to alert any minifigs that happen to be in the way.
A Lego minifig