You may have noticed different types of speed limit signs while driving without really thinking about it. The most common and easily recognized versions are usually black or white rectangular signs that provide the maximum speed limit required by law. A yellow square speed limit sign, however, is an advisory sign instead of a strict mandate.
Why Speed Advisory Signs Exist
So if there are already regulatory signs that give you the maximum speed, why would you need any other kind of speed limit warning? The answer is that some conditions that affect driving are just temporary or there may be danger ahead. Even if the actual speed limit is 50 mph, a yellow 30 mph sign is a recommendation to reduce speed. It's essentially a warning that severe weather, heavy traffic, or unsafe driving conditions exist that call for lower speed. It's common to see these advisory signs prior to sharp curves and off ramps.
Despite variations for advisory speed limit signs, they always have yellow backgrounds with big black bold text. In some cases these signs are rectangular instead of square to convey more information. The word "ramp" or "curve," for example, may be placed above the speed value to give a clearer idea how the driver should respond.
How Advisory Speeds Are Set
Unlike regulatory signs, which are determined by the law, advisory speeds are based on physics. A scientific instrument called a ball bank indicator allows engineers to analyze the force created from moving around a curve. This instrument provides a reading of zero to twenty degrees to indicate the level of force. A ten degree force, for example, suggests that drivers are aware of the danger present but are able to easily adjust speed and maintain control. Twenty degrees represents a very strong force that requires more caution. The Manual on Uniform Traffic Control Devices (MUTCD) requires that prior to placing an advisory speed sign an engineering study must be conducted.
Legal Consequences of Ignoring Advisory Signs
In most cases, ignoring an advisory sign carries no penalty, but it depends on the state and the circumstances. Even though an advisory sign is merely a recommendation to lower speed, situations exist in which you must follow them or you can be cited. If you cause an accident, for example, while not reducing speed in these areas you can be arrested and face fines for violating the basic speed law.
When Signs Are Absent
Each state has its own rules for default speeds if no regulatory or advisory signs are present. In California, for example, the default speed limit is 15 mph at a blind intersection in which there are no stop signs at any corner and it's difficult to see 100 feet ahead. But when no sign is posted, it's difficult for drivers to remember such subtleties. The state also mandates drivers to slow down in cases of heavy traffic, bad weather, or nearby children.
Drivers must make safety judgements on speed adjustment sometimes without the help of signs, especially on slick, icy, rough, or narrow roads. In any alley the speed limit is 15 mph. The question is: how many accidents occur due to drivers not knowing these default speed limits when no signs are posted? The answer is unknown, but what's clear is that the presence of regulatory and advisory signs reduces doubt and confusion.
Advisory signs add a deeper degree of safety to roads and highways, complementing regular speed limit signs. Contact Zumar at our Arizona, California, or Washington location to learn more about signs that raise driver awareness and make streets safer.