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How are Speed Limits are Set?
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How are Speed Limits are Set?

Have you ever wondered how speed limits are set? Me too! Turns out there are a lot of factors in to deciding speed limits. It’s hard to believe with today’s fast speed limits! Remember when the highest limit was 55 mph? Not until 1995 was the national maximum speed limit of 55 mph was repealed in the U.S.

Since 1995, states set their own speed limits, but still, who decides? An American Automobile Association Foundation for Traffic Safety (AAAFTS) study says there are several ways states determine speed limits. 

Most speed limits are decided by states or local governments. It is usually a balance of safety and traffic concerns. Officials don’t want to put people in danger, but recognize that roads can get backed up the speed limit is set too low. Think of your road with a lower speed limit at rush hour!

When road safety is the one and only priority, traffic concerns take a back seat. In these cases, important information like crash types and the forces drivers and passengers would experience if a collision were to happen are considered.

Other speed limits are set based on data collected from engineers’ research. While time consuming for the engineers, using scientific data to help make decisions is the safest approach to setting a speed limit. 


Not surprising, speed limits are determined by a computer program that is designed to mimic experts’ opinions. The computer uses information such as road type and characteristics, as well as traffic and crash information. However, as you may have guessed, this is not a perfect method. Don’t worry though, nearly half of experts in the AAAFTS study said they never base decisions about changing a speed limit on a computer system alone. Interestingly, 30% of respondents had never heard of these computer-based systems!  

Obviously, the overall goal is to find the best speed limit. To do this, experts also take into account how much it costs you to drive your vehicle and how much car crashes can cost. They even consider your travel time, air pollution, and the noise we all make driving around. 

Change the limits

All of this information raises an important question!  If they put so much effort into selecting the speed limit, what causes speed limits to change? It turns out the number one reason for lowering a speed limit is receiving request or complaints from the public about safety. While the top reason for raising a speed limit are simply changes in the road. 

Although speed limits may change occasionally, the majority of experts setting speed limits across the nation have a standard policy and procedure for setting speed limits. These experts attempt to take everything mentioned above and decide on the safest speed limit for everyone involved. 

So, next time you are driving just a bit over the speed limit… remember that you may be just moving your risk of crash upwards too!