Traffic lights are a combination of color and position; even if one is completely colorblind, the position of the lit lamp is sufficient to discern the signal.
The above suggestion doesn't have that sort of double-encoding of the data.
(This holds even for the odd horizontal signal, though I would expect most non-colorblind people would not be able to tell you the orientation from memory.
… and … there are plenty of drivers on the road who, judging from their behavior, would appear to be incapable of determining the color of the signal.)
