[perilunar]

With the switch from incandescent bulbs to LED traffic lights it would be very easy to change the shape of the lights: e.g. octagonal for stop, triangular for caution, and circular for go. Keep the colors, but add shape as well. Seems like an obvious and useful change to me.

[NegativeK]

That might fall apart for people with poor visual acuity.

[blincoln]

If they're roughly the same size and in the same order as the round lights today, people with poor visual acuity would still see more or less what they see currently.

[NoMoreNicksLeft]

If you can tell neither the color of the light, nor its shape...

Should you be driving?