Traffic light, no more shapes?

Question

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?

Answer 1

1. Its more expensive to manufacture and maintain different shaped lights.
2. Round hoods on each light provide better shielding against sunlight and better protection against rain (quicker dissipation) and wind by being more aerodynamic (less resistance).
3. Parts are more interchangeable. Examples: One hood fits on all the lights. The clear tempered glass cover on the red light also fits on the other lights. Clear glass is less expensive than colored glass.
4. Even color-blind people know where the red, yellow and green lights are located.
5. (not relevant to this question) Each light is now made up of a matrix of small LED's. If one LED fails, the rest keep on working. As we know, LED's are brighter, more energy-efficient and last much longer than regular bulbs.

Answer 2

I think your basic assumption that they are all the same now is wrong, or at least very locally biased. Where I'm from, there are plenty of different shapes in use. Most notable are the pedestrian lights:

However, there are many variations, even animating ones:

and ones with different count-downs:

There are also special versions for bikes:

Then, of course, there are also the arrows-type lights, in use for cars:

To conclude: it is hardly the case that there are only circles in use these days.

Answer 3

From a great distance, like traffic lights are often viewed from, it is hard to discern shapes--especially square vs. circle.

Glare and flaring tend to reduce the light to a blur anyway (except for those have 20/20 vision and perfectly clear eyeballs viewing them through a clean windshield on a clear day). The color becomes the predominant signal--and therefore it is quantity of light that becomes important.

The above examples all cut down on the amount of light leaving the signal-- especially the "bicycle" and "pedestrian" shapes (which are appropriate for the slower-moving clientele they serve, but would blur into "dim green"/"dim red" for car drivers, especially in the rain.

As @Matt mentioned in a comment to the question, the 'green' traffic lights often have a strong blue component so that RG-colorblind people have a better chance of distinguishing them, the major argument against relying solely on color.

Position provides an additional reinforcement, and a top-down arrangement is clearer than a left-right (or is it right-left?) arrangement, which was the other notably confusing thing about shaped Canadian traffic lights.