Radar speed sign

They are also used on streets that cities do not want to put physical measures on either because of snow concerns or traffic volume.

Pole mounted signs that combine speed display with variable message capability are often used in school zones, eliminating the trailer's "footprint".

Some of the features offered on the higher end signs include focused viewing systems to avoid distractions for motorists in other lanes, vehicle data collection, programmable software that allows you to determine sign behavior such as blanking/blinking speed thresholds and stealth modes, and/or access via portable devices such as Bluetooth or PDAs.

Some signs offer a flashing light to warn motorists who exceed a designated speed.

However, many state, county and city traffic engineers in the USA specify only signs that meet the federal guidelines called MUTCD (Manual on Uniform Traffic Control Devices) which, due to safety reasons, eliminate certain distracting features like strobe lights and certain color messages.

Studies conducted both in the UK and in the US have found radar speed signs to effectively slow traffic down.

The signs were most effective on streets where vehicles were driving more than 10 mph above the posted speed limit.

[9] The MUTCD (Manual on Uniform Traffic Control Devices), a standards document issued by the Federal Highway Administration (FHWA) of the United States Department of Transportation (USDOT), has specified standards regarding sign size and letter height for Speed Limit Signs (an R2-1 in the parlance) under Section 2B.13.

The third is “Guidance”, not regulation, concerning the content and color of the “legend”, typically the static signage surrounding the electronic display.

The numerals displaying the speed shall be white, yellow, yellow-green or amber color on black background.

[12] Too exhaustive to repeat here, it nevertheless addresses specific static sign color based on application, flash rates and activation speeds for violator alerts etc.

It is widely believed in the industry that the new revision of the Federal MUTCD will much more specifically address these devices and will most likely grandfather in non-compliant existing signs for some reasonable period of time.