Joachim Breitner

The merits of a yellow-red phase

Published 2018-07-30 in sections English, Reisen.

In my yesterday post on Continuity Lines in North America I mentioned in passing that I am big fan of German1 traffic lights, which have a brief yellow-red phase between the red and and the green phase (3 to 5 seconds, depending on road speed). A German reader of my blog was surprised by this, said that he considers it pointless, and would like to hear my reasons. So where we go…

Life without Yellow-Red

Lights that switch directly from red to green cause more stress. Picture yourself at the first car waiting at a traffic light, with a bunch of cars behind you. Can you relax, maybe observe the cars passing in front of you, switch the radio station, or simply look somewhere else for a moment? Well, you can, but you risk missing how the light switches from red to green. When your look at the traffic light again and see it bright green, you have no idea how long it has been on green. Hyper-aware of all the cars behind you waiting to get going, you’ll rush to get started, and if you don’t do that really fast now, surely one of the people waiting behind you will have honked.

So at the next intersection, you better don’t take your eyes off the light – or, alternatively, you develop a screw-you-I-don’t-care-attitude towards the other cars, which might allow you to relax in this situation, but is in general not desirable.

Maybe this is less of a problem on the West Coast, where supposedly everybody is nice, relaxed, and patient, and you can take all the time you want to get rolling. But in the stereotypical East Coast traffic full of angry, impatient and antisocial drivers, you really don’t get away with that.

Life with Yellow-Red

The yellow-red phase solves this problem elegantly: As long as the light is red, you don’t have to watch the light constantly and with maximum attention. You can relax: it suffices to check it often enough to catch the red-yellow phase, once every two or three seconds. When you see it, you get ready to start; and when it actually turns green, you start on time.

I would expect that it is not only less stressful, it is also more efficient: Because every car in the lane has the heads-up warning “green in a moment”, the cars can start rolling in quicker succession. Without the warning, every car to account much more for the possible slower reaction of the car before.

PS: A friend of mine wonders whether the German Yellow-Red is needed because cars with manual transmissions are much more common in Germany than in the US, and you need more time to, well, get into gear with these cars.


  1. Also Great Britain, Croatia, Latvia, Norway, Austria, Poland, Russia, Saudi-Arabia, Sweden, Switzerland, Hungary and others.

Comments

Some traffic lights in Abidjan, Ivory Coast, now have a countdown timer between red and green.

Great for street racers!

(Previously the only place I'd seen countdown timers was on Washington DC pedestrian crossings -- there they tell you how long before the pedestrian crossing goes "DONT WALK" -- super stressful).

#1 John Hughes am 2018-08-03

The Abidjan thing is interesting. It probably has a similar effect, although it precludes smart traffic lights with dynamic cycle lengths (if such a thing actually exists).

Pedestrian crossing count downs are actually common all over the US, as far as I can tell. I often use the count down of the cross section to see how long it takes to turn green for me... But why do you find it stressful? Isn't it more stressful if the light turns red unexpectedly while you cross the road?

#2 Joachim am 2018-08-03

Not sure really, I guess because without the timer I assume that the delay between DONT WALK and green for cars is enough for me to get across the street, but with the timer I seem to be calculating "hum, 3 seconds, can I make it in time?"

#3 John Hughes am 2018-08-04

As far as I know, the delay afterwards is still big enough, i.e. it doesn't change that aspect. But I am not 100% sure, so I see how that ambiguity can cause stress. UI is tricky!

#4 Joachim am 2018-08-04

The yellow-red phase has another advantage: When approaching a red light, you can adjust your speed to not come to a full stop right before it switches to green, but rather to coast into the crossroads. This allows for more fuel efficient driving.

Austrian traffic lights also have the reverse: The green light starts flashing a few seconds before it switches to yellow. Thus, yellow becomes the phase in which you only expect overly fast cars, unattentive and taxi drivers to cross, and barely anyone enters the crossroads at red.

#5 chrysn am 2018-08-06

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