Why Do Some Speed Limit Signs Say 'Radar Enforced'?

Since the 1900s, speed limit signs have attempted to keep roads safe and traffic moving. Initially set by individual states, federal speed limit laws were passed in the 1970s. Suffice to say, speed limits are a law that must be followed; and speeding can lead to tickets (or worse). In fact, even going too far below the speed limit can get you in trouble. That's why some speed limit signs say "radar enforced" – the law is taking it seriously. 

If you see a speed limit sign that says "radar enforced," that means there may be a police officer using a radar to measure the speed of passing cars from a hidden spot. More commonly, there maybe a speed camera using LIDAR sensors to capture speeds. When it detects a speeding car, the camera will capture a photo or video as evidence. It is then reviewed by law enforcement before a ticket is issued (although some states are attempting to implement a system sans police). 

The reason that speed limit signs say "radar enforced" is because it can be seen as a legal gray area to set up "speed traps." The specific laws vary from state to state, but a speed trap generally refers to law enforcement using stealth to catch speeding drivers. Oftentimes, the area where a police officer is hiding must be a marked section of the road and there must be signs to let drivers know there are speed cameras. However, it will likely be very difficult to fight a speeding ticket in court with the "speed trap" defense. 

To avoid getting caught speeding, the best thing to do is to pay attention to the speed limit signs and stick to those speeds. If you are still nervous, there are some apps that will notify you that police are in the area with live updates from other drivers. Police are often waiting in certain areas where drivers are likely to speed — these legal speed traps often include on-ramps. They may also be in construction and school zones, which often come with larger tickets.