Studies show that adjusting speeds by as little as 2 to 5 mph may save lives in pedestrian-related accidents. Photos: Information Display Co.
Scheduled to turn on automatically during school hours, a radar display takes the guesswork out of speed limits.

Most drivers don't purposely exceed the speed limit but get distracted around school zones, work zones, and other areas where attention to pedestrians is critical. Technological advances and research regarding effectiveness are prompting more departments to solve this problem by specifying radar speed signs. The signs refocus drivers' attention to their actual speed in relation to the posted limit.

A 2005 report by the Maryland State Highway Administration found that trailer-mounted radar speed signs increased compliance by 10 to 40 percentage points. A 1998 study conducted by TranSafety Inc., an independent road transportation and safety agency, concluded that although photo radar reduces speeds, radar speed signs offer better overall results. That same year, a study sponsored by the Automobile Club of Southern California found that unenforced radar speed signs (without police accompaniment) offered the most cost-effective traffic-calming solution of several tested.

All of this has led to an increase in the number and variety of display models since their introduction to the U.S. market in the 1980s, expanding the range of options to consider before specifying.


A well-designed radar speed display will provide years of low-maintenance service. So if you plan to apply a government grant toward the purchase of displays, make sure it complies with the Federal Highway Administration's Manual on Uniform Traffic Control Devices (MUTCD). Some models are fully compliant, while others may comply only with certain provisions. For instance, the size of a display may be within guidelines, but the color or materials may not. Ask the sales representative about the specific regulations for your region.

The next consideration is effectiveness. No matter how clear or attention-grabbing a sign may be, it won't be effective if drivers don't take it seriously. It should be designed to quickly gain attention, convey a clear message, and command respect.

Drivers are more likely to dismiss unofficial-looking and malfunctioning signs. Is the display easy to read from a distance? Does it use standard road sign colors? Is the font a traditional shape and size?

Poorly designed speed displays may produce erratic readings when multiple vehicles approach or when opposing traffic passes at the same time the target vehicle is approaching. A substandard sign may also display inaccurate speeds. Ask the manufacturer to let you test the unit before making a purchase.

Today's more advanced signs use LED technology rather than the older mechanical flipping mechanism to display numerals and other changing messages. The low-energy lights are less prone to mechanical failure and provide high visibility day or night. Quality can differ from brand to brand, so compare the brightness of each display.

Although they lose their brightness over time, the way in which current is applied to the LEDs makes a big difference in longevity. Signs that use direct current to the LEDs will be bright and clear long after signs using a multiplex design (LEDs that switch on and off multiple times per second) have degraded. If this information isn't listed in the unit's specifications, check with the manufacturer.

Some displays use technology to reduce glare and increase contrast. For example, a masking design helps ensure the display is visible only to drivers passing directly by the sign. The inability to read the display from acute angles helps prevent “rubbernecking” and other potentially hazardous driving conditions.