[331c8c71]

It's simpler than that, one can only change lanes when they are separated by a dashed line. Solid lines you are not supposed to cross.

[gpvos]

Well, there are bidirectional roads with dashed lines in the middle, so you can overtake, but you should obviously not stay in the lane with oncoming traffic for longer than that. I can see how colours can help there, but in Europe the road situation tends to be clear enough that that isn't necessary.