Speed limit signs can either fade into the background or startle us to attention, often depending on how fast we might be going. Familiarity plays a role too. We expect to see 25 mph in a quiet residential neighborhood and 55 or 65 mph on a busy highway. But what if you were driving along and saw 8.2 mph, or 14.4? Most speedometers don’t even display tenths of a mile per hour, so how is a driver supposed to follow a rule of the road like that?
It sounds ridiculous, and it is a bit uncommon, but speed limits expressed in decimals definitely do exist. To explain what’s going on, Reader’s Digest reached out to Michael Knodler, PhD, a professor of civil and environmental engineering at the University of Massachusetts Amherst and the director of the UMass Transportation Center. Read on to find out the purpose behind these unusual speed limits and whether they might soon appear on a road near you.
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How long have we had speed limits?
Speed restrictions date all the way back to the days of non-motorized transportation, though they were a little more loosely defined. As far back as 1652, officials in what was then known as New Amsterdam—now New York City—declared that no wagons, carts or sleighs “shall be run, rode or driven at a gallop,” according to History.com.
With the arrival and proliferation of the automobile in America in the late 19th century, formal speed limits soon followed. Connecticut is widely credited as the first state to enact an official automobile speed limit in May 1901, setting a maximum speed of 12 mph in cities and 15 mph on country roads. The most important provision? Drivers had to slow down or even stop when encountering horse-drawn vehicles so that they wouldn’t startle the horses.
Automobiles continued to improve and become faster as time wore on, but there were no official national speed limits in the United States until much later. In January 1974, President Richard Nixon, responding to the oil crisis and skyrocketing fuel costs, signed legislation that established 55 mph as the maximum speed allowed nationwide. That federal limit stood until 1995, when authority for setting speed limits was returned to states and local jurisdictions.
Today, speed limits vary from place to place. The Federal Highway Administration notes that some common limits include 25 mph in residential or school districts, 55 mph on rural highways and 65 to 70 mph on rural interstate highways. The highest posted speed limit in the country is 85 mph, found on a stretch of Texas State Highway 130.
Why do some speed limit signs have decimal points?
There are two main reasons jurisdictions or property owners might post odd speed limits like this, according to Knodler.
- It stands out. “Seeing a nonstandard limit captures your attention, given its uniqueness,” he says.
- It seems important. He also says adding a decimal place “implies a level of specificity that might make it appear really accurate or important.”
The idea gained attention when drivers in Appleton, Wisconsin, were recently greeted with a 17.3 mph speed limit at the Outagamie Country Recycling and Solid Waste Facility. According to a Facebook post introducing the new speed limit and sign to the public, safety was the No. 1 reason for the new eye-catching speed limit.
How effective has this been at lowering the number of accidents?
The effectiveness of these types of speed limits remains a bit of a question mark, according to Knodler.
Most research on unique speed limits hasn’t focused on those with decimal points, in part because they are not technically supposed to be used on public roads. “The evidence to date would be mostly anecdotal, but it would be easy enough to study if there was interest,” he says.
One thing that is clear, however: Any measure that encourages drivers to pay closer attention behind the wheel can be a positive step in the direction of creating safer roads.
Where are you likely to find these quirky signs?
Official statements about decimal speed limits are scarce, but signs with unusual speed limits are often found in semi-private residential developments, private properties and other areas where property owners may install their own traffic signs, even if they don’t necessarily comply with roadway standards.
“It’s really a bit of a gray area,” Knodler says, explaining that the Manual on Uniform Traffic Control Devices is the federal standard and requires speed limits posted on roads that “are inviting of the public”—including some seemingly private areas such as condominium complexes—need to meet certain requirements. They must be based upon an engineering study, be in increments of 5 mph and be displayed on a white regulatory sign with black letters.
So why do these signs continue to appear in places when they don’t meet those requirements? “There are plenty of examples of noncompliant traffic control devices everywhere,” Knodler says. “I joke that I give my students an assignment every year to go out and find a noncompliant TCD, and it is the easiest assignment because they all get 100%.”
Are we going to see more of them across the country?
For now, these signs remain a curiosity more than anything. Official traffic signs are strictly regulated, and the likelihood of widespread adoption is slim. Still, says Knodler, “they are fun, and, as mentioned, attention grabbing.”
Sources:
- Michael Knodler, PhD, professor of civil and environmental engineering at the University of Massachusetts Amherst, director of the UMass Transportation Center and director of New England University Transportation Center; email interview, July 2026
- History.com: “Connecticut Enacts First Speed-Limit Law”
- Federal Highway Administration: “Speed Limit Basics”
- Independent: “Decimal Point Added to Speed Limit Sign to Stop Drivers from Going into ‘Autopilot’”
- Facebook: “Outagamie County Recycling and Solid Waste New Speed Limit”
The post No, You’re Not Hallucinating—There’s a Decimal Point on That Speed Limit Sign. Here’s Why appeared first on Reader's Digest.
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