Solid State UX

How do you know if you are well suited to a career in information architecture?   Well, here’s a little test.  When you are finished reading this post, follow the link I provide to the US Department of Transportation’s Manual on Uniform Traffic Control Devices(MUTCD), which is the definitive, 864 page style guide for the country’s road signs, signals, and traffic markings.  If you soon find yourself delightfully lost in the visual minutiae and obscene specificity of the guidance provided, then you are either Rain Man or what I suspect is a natural born IA.

A new version of MUTCD was published December 16th, 2009 – the 10th edition in 74 years.   No document quite illustrates how design affects our daily lives and safety greater than this one does.  Most of the nuances of driving a car are deeply internalized by us drivers, so it’s not always obvious that the traffic experience is as designed as it actually is.  Take the shapes of regulatory signs, whose shifting geometry roughly correlates the number of sides of a sign to the intensity of the approaching danger ahead.  Stop signs (8 sides) are much sterner in their warning than diamond shaped Slow signs or triangular Yield signs. Circular signs, such as those at a rail-crossing, signal the most danger of all.  Afterall, the number of sides of a circle is infinite.  This dates back to a scheme created by the very first attempt to standardize signage in the early 1920’s.

Speed Hump is the correct term, but they offer the less hilarious "bump" option as well.

MUTCD takes careful consideration not to use traffic-planner jargon in such a way as to confuse drivers (or – let’s face it-make them laugh), even if comes at the expense of introducing misnomers and contradictions into their system of wayfinders.   Any leftish turn requiring a driver to initially make a right turn, such as those looping lefts on highway onramps, is called a “jughandle” turn by the pros, not a U-turn or a Left Turn, but the sign will say something like “U-Turn from Right Lane.”  A lesson to interaction designers – favor literalness over jargon in navigation.  A road-bump is actually technically a “hump,” but the sign says Bump anyways to avoid dangerous snickering by amused drivers.

Night speed limit signs are rendered in black with white characters - symbolizing "night" but sacrificing retro-reflectivity.

Information design, particularly color and iconography, is fussed over perhaps most of all.    Florescent yellow is the color of choice for most signs due to it’s high luminance and saturation – a combination that allows it to be seen in day, night, dawn, dusk and fog, with or without headlights.  The color yellow is also highly durable, meaning it takes longer to lose its’ color and retroreflectivity than other colors and making it a safe choice for a road sign’s design.  Curiously, the approved sign for showing night speed is an all black background with white characters – the black itself communicating “night-time” but making it less visible in the very time for which it is intended.

Purple is never used for lights or LED signs in traffic control even though it is high contrast.

Purple, it turns out, is also a very safe color due to it’s high contrast and saturation  – particularly Pantone^® Matching System^® (PMS) 259 (the exact color used by 13 states for E-Z Pass lanes).  Ever wonder why there are purple signs on those E-Z pass lanes but no purple lights or LED signs?  It’s because of a phenomenon called small-field tritanopia, which results in a “loss of sensitivity to blue light when the signal appears very small. As a result, a purple light might appear red with a blue haze surrounding the signal, potentially causing confusion that could result in erratic behavior as drivers approach toll booths.”  This is one reason why purple was not used much until recently as a road sign color, even though DOT has had it on it’s official “reserved” color list for decades.

Iconography is fussed over, but strangely optional.  Nearly every bit of icon bearing signage in the MUTCD offers up an icon-less alternative.   They seem to be saying, well if you’re an icon type go with this – but we understand some municipalities are just not into icons. Does that mean one is just not safer than the others?  Are there not studies proving that icons add important non-verbal cues and contribute to highway safety?

Use icons or don't use icons. What do we care?

Huh? The limitations of stand-alone imagery in road-signage.

And it’s interesting that traffic control designers face some of the same types of challenges that web designers do.  One central debate is clutter and the competition for that scarcest of all resources -even amongst drivers – attention.  Afterall, the MUTCD was started as a reaction to too many signs.  In the very early days of the automobile, local auto clubs used to put up signs and sometimes there would be 10 or 11 signs for a single popular road or attraction.

How many signs does it take? Well, enough to get the job done but not so many that drivers "consume" the safety benefit.

But how many signs is too many when it comes to public safety? Do signs cancel one another out like sidebar ads on a website?  It turns out that more road signs do not lead to greater safety, but not because drivers don’t notice them.  It has more to do with what an economist would call ‘consumption’ of the safety benefit provided by the extra signage.  If a driver is given a safety improvement, such as clearly marked lanes, signs, lights, etc. – she will “consume” the benefit and drive faster as a result.   So, guess what, it turns out traffic circles have less accidents than traffic signals – because drivers understand they are responsible for their own risk, shifting risk away from that of government.   It’s a paradox that web designers just don’t have to deal with.

Related Posts from Around the Web:

The Manual on Uniform Traffic Control Devices (MUTCD)

Distracting Miss Daizy – The Atlantic Magazine