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What an Advisory Speed Limit Sign Means

February 20, 2020

While the Federal Highway Administration oversees broad regulations for traffic signs, it’s up to states and local governments to determine the speed limits for their respective jurisdictions. States usually set the limits for freeways, while cities operate within laws of higher authority and set speed limits on streets. Sometimes an advisory speed limit is needed for temporary purposes or dangerous locations to account for weather, road conditions, events or accidents.

Regulatory vs Advisory Signs

A regulatory sign reminds drivers of a specific law they must follow, whereas an advisory sign merely recommends they pay attention to certain factors for safety precautions. The two different sign types are easy to tell apart, since regulatory signs are black and white, while advisory signs are either yellow or orange with black lettering. Regulatory signs may either be black letters on white backgrounds or the inverse.

The main takeaway is that advisory signs are simply warnings. They can be permanent or temporary, depending on the situation and where they are placed. Typically, advisory signs are used on exit ramps with a recommended speed limit that is usually much slower than the normal speed limit. They are also used on sharp curves and in places where truckers are in danger of tipping over. The recommended speed is posted to advise drivers who may not be aware of the possible dangers of driving even under the speed limit.

Electronic Advisory Signs

Since there are various situations when an advisory speed limit sign needs to be placed in an area for a temporary period, many cities are finding it economical and convenient to use portable electronic displays for these purposes. A leading manufacturer of these battery-powered mobile signs on wheels known as dolly mounted signs is TraffiCalm, which makes a diverse line of traffic control products.

This modern electronic device uses bright LED displays that drivers can see from a distance, which prepares them to slow down. The machine can be customized to display whatever message traffic control officials want to communicate to drivers. It can be used for a variety of reasons, including displaying a driver’s current speed based on radar technology. Officials have options to make the text flashing or static.

Sometimes a dolly mounted electronic sign is used to display advisory speeds due to various adverse weather or road conditions. Slippery roads following an oil spill or a mudslide often call for the use of some type of speed advisory. Thick fog or heavy rain may also be the reason to roll this device to the side of the road to alert drivers to be more careful.


An advisory speed limit is posted as a suggestion for motorists to drive slower than the official speed limit, whereas a regulatory speed limit sign mandates drivers must not exceed the limit. Local governments that want to save time and money installing these signs should consider a portable dolly mounted electronic sign. Contact Zumar at our Arizona, California or Washington location to learn more about the use of advisory speed limit devices.

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