It depends on their kind of colorblindness.

I see green lights as white, which is fine most of the time because of the order.

The exception is when there's a lot of glare from the sun setting behind me, and I sometimes can't tell if it's green, or just the sun reflecting at the right angle. It also washes out the red and yellow, making it harder to see if they're lit.

Funny thing, I'm NOT colorblind and apparently I only rely on the color. I've been driving for over 10 years now, mostly in the capital that has traffic lights everywhere, and sitting at my desk now not looking at a traffic light, I wouldn't want to bet money on the order.

Yes. They can still drive fine, but don't get the benefits of color coding, like being able to infer whether red or green is lit from the light reflected off of other objects. That becomes somewhat important in low visibility situations where the position is hard to determine.

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.

Horizontal lights are not consistent across countries. The linked article has an image of a Japanese horizontal traffic light with red on the right, whereas an American traffic light would have red on the left.

> The order of the lights doesn't change.

For 3 lights streetlights no. For 2 lights streetlights it depends. They can be (in DE) either red and yellow or yellow or green.

Almost fifty years ago, I worked with a guy who was color-blind. This was in Colorado, where at the time some of the little towns in the mountains still had traffic lights arranged horizontally rather than vertically. He must have known the order at one time--I think I learned it for my license test--but of course with little chance for reinforcement tended to forget. I suppose that such lights are all gone now.

Most color blind have issue to see shades and subtle differences. They see red and green just fine.

The people who do not see red at all however, see red as black. So, they do not see red traffic light at all.

> The order of the lights doesn't change.

That argument has two issues: First, not all US traffic lights have order, as single-light ones replace stop signs in some (mostly suburban/rural) areas. Second, light position is still hard to discern at night.

My personal take: the red and yellow hues in traffic lights are often indistinguishable for those of us with red-green colorblindness.

Night time?