Why Traffic Signs Work

A driver going 55 miles per hour needs about 280 feet of stopping distance — almost the length of a soccer field. So, if you’re trying to communicate to highway drivers, you have just a few seconds to get across important messages like this one:

The driver of any vehicle shall not turn such vehicle so as to proceed in the opposite direction unless such movement can be made in safety and without interfering with other traffic.

No vehicle shall be turned so as to proceed in the opposite direction upon any curve, or upon the approach to or near the crest of a grade, where such vehicle cannot be seen by the driver of any other vehicle approaching from either direction within five hundred feet.

Try posting that on a road sign.

Luckily, the people who design traffic signs came up with a solution that allows them to translate the full meaning of those two paragraphs into this:

This sign works — and works quickly — because it sticks to a few important rules.

On traffic signs, red always means “no” or “stop.” A vertical rectangle is always used to tell a driver about a regulation. These and other rules are spelled out in a detailed document called the Manual on Uniform Traffic Control Devices (MUTCD). The MUTCD states: “Uniformity of traffic control devices is critical in highway safety.” It adds that uniformity also creates efficiencies, helping public agencies simplify maintenance and control costs.

Of course, traffic signs rely on more than shapes and colors; they use words and symbols, too. So the MUTCD includes specific guidelines for lettering, size, borders, arrows, and more.

It may seem odd for a communicator to be extolling the virtues of uniformity. Numerous laboratory experiments have found that creative messages (those that feature unusual and nonobvious solutions) get more attention, lead to positive attitudes, and are more effective at influencing behavior.

But, successful communication also relies on a certain amount of predictability. Imagine if your grocery store or your bank’s website shuffled its sections around each week. We’d spend more time searching than getting — and that’s a sure way to get your audience to stop paying attention.

Lastly, the MUTCD states that an effective “traffic control device” meets five basic requirements. It must:

• Fulfill a need
• Command attention
• Convey a clear, simple meaning
• Command respect from road users
• Give adequate time for proper response

These “rules of the road” would serve any communicator well.

By the way, the MUTCD permits use of 13 colors on road signs. Two of those are coral and light blue, which are reserved for purposes that haven’t been determined yet. (Keep an eye open for those pink traffic signs.)