What about Speed Limits?

Editor’s Note: This blog post first appeared on NMA’s Driving in America blog in February 2018.

Have you ever noticed while driving that generally the experience is fairly civil? Not too much chaos…not too many drivers overdoing it. We all drive along because in reality we just want to go where we need to go without too much hassle.

Funny thing is…most of us drive at a speed we feel comfortable driving whichever road we happen to travel…we go with the flow of traffic and if there are no outliers (someone driving too fast or too slow), everyone gets to where they need to be intact and hopefully on time. Most of us want to abide by the law but speed limits sometimes are set too low with the type of road and the flow of traffic.

The NMA’s 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).

These limits should be periodically adjusted to reflect changes in actual traffic speeds.

What is a Realistic Speed Limit?

A realistic speed limit should invite the public to comply by conforming to the behavior of most drivers. A tried and true method of determining a realistic speed limit is done by traffic engineers who study the free flowing traffic and adjust the speed to the 85th percentile. Numerous studies have shown that the 85th percentile is the safest possible level at which to set a speed limit. If the intersection yellow lights are then timed properly to the street’s speed limit then drivers and all users of the intersections such as motorcyclists, bicyclists and pedestrians should be safer.


Photo attribution: Joshua Putnam licensed under Creative Commons 2.0 Generic (CC BY 2.0)

Slower is not Safer

Numerous federal and state studies have indicated that drivers will more likely get into an accident if they are traveling significantly below the average speed. According to an Institute of Transportation Engineers study, those driving 10 mph below the prevailing speed are six times as likely to be involved in an accident. When the majority of traffic travels 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. A reasonable speed limit helps traffic to flow at a safer and more uniform pace.

If the speed limit is raised higher, wouldn’t everyone just drive faster?

No because the majority of drivers will not go faster than what they feel is comfortable and safe regardless of the speed limit.

NMA Founder James J. Baxter, in a piece he wrote called the Truth about Speed Limits, dispels the myth of whether speed limits can and should be used to control overall traffic speeds.

This myth haunts us like bad breath after a night of beer, pizza, and cigars. Speed limits have virtually no influence on regulating general traffic speeds. The only legitimate function of speed limits is to delineate at what point reasonably competent drivers exceed the safe speed for a given roadway. If the speed limit is properly set, it can serve as a useful form of information as well as a “trigger” for enforcement action. The speed limit will only function if it is set to reflect prevailing speeds. 

The NMA was founded because the federal government imposed a 55 mph speed limit experiment on all vehicles for 22 years that unequivocally proved that speed limits do not determine traffic speeds.

Contrary to safety officials who continue to tell us that we are driving too fast and have more accidents than ever before…they are just plain wrong. More people than ever before are driving more miles than ever before and statistically speaking there are less accidents and fatalities per miles driven. Each year the rise in fatalities correlates to the rise in more people driving more miles. Distracted driving is also a much bigger problem than it was even just five years ago.

Speed Limits are under attack more so than ever before with programs like Vision Zero, Smart Streets and Complete Streets. If you want to get involved in advocating for realistic speed limits in your state or city, check out NMA’s Model Speed Limit Law which includes some definitions that are important to know. Also, we encourage you to join the NMA for use of additional advocacy materials reserved for members only.

Be safe out there!

Driving in America, a new blog by the NMA, shines a spotlight on specific issues that affect motorists across America.

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