My issue with give way lines is that it would be a little overpowered in the context of the game.
It's worth testing give way signs. They wouldn't work on some levels, like the round about (where you would normally have give way signs) because there's just too many cars. But on other road layouts where you have created several slip roads and the traffic isn't too high it could work. Makes sense instead of the car just driving out. But it would change the game, so should be tested first