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Usability of Everyday Things – Traffic Lights


In my way back home from the office sometimes I have to pass this traffic light, it’s at one end of Butt Bridge at the corner with Eden Quay, in Dublin (Ireland). The driver that arrives at the stop from the bridge can choose between three directions: left turn, right turn and straight. When the “system” is in “full green” status (Figure 1) there are no problems on understanding what to do, you can pick one of the three options (right, left, straight) and continue your journey.

Figure 1 - Green Light

But when the “system” is in “mixed colors mode” (Figure 2 and 3) I’m almost sure that more than one driver is left in a status of confusion.

Figure 2 - Green and Red, wtf?

Figure 3 - Detail

From the distance the big red light will catch your attention, both because red is the color of danger and also because we are used to recognise a pattern of three vertical lights on traffic lamps (with only one light on at any time). You will be tempted to reduce the speed and stop and this is what really happens quite often, with just a wait of a couple of minutes close to that cross is enough to realize it. Most of the time it takes some seconds for the car driver to understand that the green arrows on the left are eventually giving him/her the right to turn left or go straight.

On top of this, if you think that Dublin is a touristic destination for many Europeans that are used to drive their cars on the right side of the street and not on the left like in Ireland, it’s easy to imagine that just the task of driving on the “wrong side” will consume a lot of cognitive resources of a driver that will end in a frustrating experience. In my opinion, adding also a confusing street sign can lead to major problems (namely car accidents).

You don’t need a degree on usability to understand the big mistakes made designing this interaction: why using the sign “stop everybody”/red light to only stop cars turning right?, why using two more lights to override the main sign building thus a very strange and unusual configuration of the system?

Funny enough I’m not the first one spotting bad traffic lamps in the Dublin area, here an article http://www.iqcontent.com/blog/2007/06/the-usability-of-traffic-lights about Dun Laoghaire (south Dublin Bay)

2 Responses to “Usability of Everyday Things – Traffic Lights”

  1. Michael Alexander

    The easiest way to fix the problem you describe is to have three traffic lights next to each other:

    The left set has a red, yellow and green left arrow.
    The middle set has a red, yellow and green upward arrow.
    The right set has a red, yellow and green right arrow.

    The the situation that you show would be perfectly clear to everyone:
    - A green left arrow
    - A green upward arrow
    - A red right arrow

    The problem is being caused because the normal green light signals to most motorists, that it is safe to pass. Change all the glasses to ones with arrows in them, and the situation becomes clear.

    Q.E.D

  2. Arjuna Del Toso

    @Michael Alexander
    Finding a solution is not difficult once you have spotted the problem, the thing that make me think is that apparently nobody raised any doubt about that traffic light during the project phase …



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