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Speed Limits


Speed Limits: Frequently Asked Questions

Q. How should speed limits be set?
A. Traffic engineers maintain that speed limits should be established according to the 85th percentile of free flowing traffic. This means the limit should be set at a level at or under which 85 percent of people are driving. Numerous studies have shown that the 85th percentile is the safest possible level at which to set a speed limit.

Q. What are "realistic" speed laws?
A. According to a pamphlet produced by the Washington State Department of Transportation relating to speed limits, "realistic" speed limits should invite public compliance by conforming to the behavior of the most drivers. This would allow the police to easily separate the serious violators from the reasonable majority.

Q. Isn't slower always safer?
A. No, federal and state studies have consistently shown that the drivers most likely to get into accidents in traffic are those traveling significantly below the average speed. According to research, those driving 10 mph slower than the prevailing speed are more likely to be involved in an accident. That means that if the average speed on an interstate is 70 mph, the person traveling at 60 mph is more likely to be involved in an accident than someone going 70 or even 80 mph.

Q. Wouldn't everyone drive faster if the speed limit was raised?
A. No, the majority of drivers will not go faster than what they feel is comfortable and safe regardless of the speed limit. For example, an 18-month study following an increase in the speed limit along the New York Thruway from 55 to 65 mph, determined that the average speed of traffic, 68 mph, remained the same. Even a national study conducted by Federal Highway Administration also concluded that raising or lowering the speed limit had practically no effect on actual travel speeds.

Q. Don't higher speed limits cause more accidents and traffic fatalities?
A. No, if a speed limit is raised to actually reflect real travel speeds, the new higher limit will make the roads safer. When the majority of traffic is traveling at the same speed, traffic flow improves, and there are fewer accidents. Speed alone is rarely the cause of accidents. Differences in speed are the main problem. Reasonable speed limits help traffic to flow at a safer, more uniform pace.

Q. Aren't most traffic accidents caused by speeding?
A. No, the National Highway Traffic Safety Administration (NHTSA) claims that 30 percent of all fatal accidents are "speed related," but even this is misleading. This means that in less than a third of the cases, one of the drivers involved in the accident was "assumed" to be exceeding the posted limit. It does not mean that speeding caused the accident. Research conducted by the Florida Department of Transportation showed that the percentage of accidents actually caused by speeding is very low, 2.2 percent.

Q. Aren't our roads more dangerous than ever before?
A. No, our nation's fatality rate (deaths per 100 million vehicle miles traveled) is the lowest it has ever been. The total number of fatalities has also stayed relatively stable for several years. They do occasionally increase, but given that our population and the distance the average person drives are also increasing, this is not surprising, nor is it cause for alarm.

Q. If nobody follows the speed limit, why does it matter that they are underposted?
A. According to a speed-limit brochure published in conjunction with the Michigan State Patrol, inappropriately established speed limits cause drivers to take all traffic signals less seriously. The brochure also points out that unrealistic speed limits create two groups of drivers. Those that try to obey the limit and those that drive at a speed they feel is safe and reasonable. This causes dangerous differences in speed.

Q. Don't lower speed limits save gas?
A. No, research has shown that the 55-mph National Maximum Speed Limit, which was enacted specifically to save gas, had practically no impact on fuel consumption. This is partly because people do not obey artificially lower speed limits. It is also because the differences in travel speeds that result from unreasonable limits waste gas. Most fuel is used to accelerate to a given speed. Speed limits based on actual travel speeds promote better traffic flow, which reduces the amount of braking and accelerating on our roads. This has a positive effect on fuel consumption.

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NMA Position on Speed Limits

Speed limits should be based on sound traffic-engineering principles that consider responsible motorists' actual travel speeds.

Typically, this should result in speed limits set at the 85th percentile speed of free-flowing traffic (the speed under which 85 percent of traffic is traveling).


NMA Speed Limits Fact Sheet

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