It seems that practically every city has a slightly different way of indicating pedestrian and/or vehicle signals. I especially noticed this, what with my recent trip to Europe. Essentially, they differ in the ways that the signal changes to inform you of whether you should proceed. The way I see it, a good design maximizes the information provided, the ease of comprehension, and minimizes cost. The least information given are signals that have two values, “go” and “don’t go.” If you don’t actually see the change from “don’t go” to “go,” it means that you have no idea how long “go” will remain the state, and whether it is really appropriate to go.
A ternary system is better than a binary one, because at least you have an idea that it will soon change to “don’t go.” I love when they replace a ternary pedestrian signal with one that counts down. Everyone has their own speed, they know how long it will take them to walk across the street, and knowing the number of seconds remaining, can properly evaluate whether or not to proceed.
One option that I found recently (via information aesthetics) is the Marshalite, a traffic signal that is essentially an analog clock, with the traditional traffic indicators of red, amber, and green around the circle. Apparently it was used in Australia for decades. I think it is fantastic, providing people with perfect information about the current status and how long until it will change. I think we could do a lot worse than switch to these everywhere. Some might argue that this is not simple to understand, but I don’t believe that. The Wikipedia article suggests that this method can’t cope with changing durations, but I have no doubt that it could be modified to handle that.