Traffic light, no more shapes?

I remember when I was a kid. Each traffic lights had different shapes. Red = Square, Yellow = Triangle, Green = Circle. Now all the traffic lights that I see are round.

Is there a reason why they don't need to have different shape any more?
Isn't it harder for people that have trouble with colors?

(Source: http://en.wikipedia.org/wiki/Traffic-light_signalling_and_operation#mediaviewer/File:Colourblind_traffic_signal.JPG)

_{(source: dec-ced.gc.ca)}