The GPS works as you might think it would work, it paints a line on the road showing the driver where to go.
This technique is very similar to the one shown in racing computer games, in these there called "Driving lines". They tell the user where to put the car to get the best speed. Obviously the car assitance will not want the driver to drive faster, but get to where they want to go.

As you can see from the image above, the driving aid isn't too overpowering so the user can still appreciate the graphics in the game. However in the driving assitance system, the driving line, along with the arrows would be a lot clearer.
This feature of the system would also have a distance counter, to allow the driver to see how far he has got left to get to their destination.
It would also have direction arrows to tell the driver where to turn.
This feature of the system would also have a distance counter, to allow the driver to see how far he has got left to get to their destination.
It would also have direction arrows to tell the driver where to turn.