Do Speed Limits Even Work Anymore?

Speeding is the most common law broken in the United States. Multiple studies over the years have found that over half of all drivers admit to exceeding the speed limit by more than 15 mph at least once in the last month. Not only that, but limits across the country, on all kinds of roads, are steadily rising over time. We ask, respectfully: are speed limits even working anymore?

That’s what I’m digging into in this week’s YouTube video. I want to clarify a couple things up front. No one is saying that we should get rid of all speed limits. They’re absolutely vital to road and pedestrian safety in many cases, like in towns, dense cities, suburban neighborhoods, school zones, etc. It’s just physics: the higher the speed, the worse the crash. The problem is the way they’re set, which is something called the 85th percentile rule.

Sign up for The Drive Daily

Get the latest car news, reviews, and features.

By signing up you agree to our Terms of Service and Privacy Policy.

Periodically, traffic engineers conduct a study on a given road to determine the max speed at or below which 85% of drivers are traveling. That becomes the new speed limit. But, hang on—if more than half of drivers are speeding, doesn’t that mean the limit is being constantly raised by speeders? Essentially! It’s not like speed limits are reset every year, but over time, they go up.

This is especially noticeable in places like a major multi-lane surface street (stroad!), which despite being lined with businesses and driveways and cross cut by intersections, now has a 45 mph speed limit (which means people are doing 60) because the design of the road accommodates people who want to go faster. This drastically increases speed variability, which is the difference in speed between you and everything else on or around the road: other cars, pedestrians, or power poles. And that is when speeding becomes truly dangerous.

And why don’t we just lower the limit on that road? Well, in this specific example, that’s actually going to make speed variability worse. By now, what started as a wide, slow-paced boulevard in the 1940s has been developed into an arterial route accommodating those higher speeds. Hell, it encourages them. Lowering the limit will prompt a large chunk of drivers to slow down—but another large or even larger chunk will continue to speed, spiking variability.

On the highway, it’s a slightly less complicated story. The German Autobahn—where less than 10% of Germany’s traffic fatalities occur—proves it’s possible to have a safe highway network with no speed limit. The reasons why we can’t do that here in America are logistical: we don’t train our drivers or maintain our highways like the Germans. The reason it works over there isn’t just that Germans are more organized. It’s because conceptually, raising or removing a highway speed limit naturally prompts a smoother traffic flow.

What it doesn’t do is magically make high-speed crashes less severe, obviously. But consider this: America had a national 55 mph speed limit from 1974 to 1995. While it was enacted because of the ’70s oil crisis, it stuck around because it clearly reduced highway fatalities. When Congress repealed it, limits immediately started going up—yet highway fatalities continued to drop until reaching a 40-year low in 2014. Raising the limits didn’t make the roads safer—advancements in auto safety standards did—but they didn’t make them more dangerous despite millions more cars on the road.

So, do speed limits work? It depends on where you look. But unless there are changes made to the way they’re set and updated, they’ll always feel caught between a mandate and a polite suggestion, forever a moving target.