AAA Study Examines the Impact of Changing Speed Limits

A new study from the American Automobile Association (AAA) has suggested that raising vehicle speed limits offers negligible benefits to drivers while decreasing overall safety for all travelers.

“Our study analyzed before-and-after data on a dozen roadways that raised or lowered posted speed limits and found no one-size-fits-all answer regarding the impact of these changes,” said Dr. David Yang, president and executive director of the AAA Foundation. “However, it is critical to consider the safety implications when local transportation authorities contemplate making changes with posted speed limits.”

AAA found that raising posted speed limits “was associated with” increased crash frequencies and rates for two of the three Interstate Highways examined. Note that it didn’t attribute the uptick in wrecks to a change in speed. That’s likely because we’ve seen a generalized increase in accidents across the country these last few years and the fact that there could be other factors at play (e.g. worsening road conditions or more substance abuse). While useful, these studies aren’t done in a laboratory with a control group and there’s no way to change that.

The association even noted that data from the National Highway Traffic Safety Administration (NHTSA) indicated there were more than 42,000 traffic deaths in 2021 and again in 2022, the highest levels in 16 years. The NHTSA believes that speeding was a factor in nearly 29 percent of the fatalities in 2021 and 27 percent in 2022.

Meanwhile, lowered posted speed limits were associated with decreased crash frequencies and rates for one of the two principal arterials examined. This is out of the six stretches of road it examined that had their limits lowered vs the six portions of pavement it monitored that had their speed limits raised.

Either way, AAA said the “changes in travel times were small in response to both raised and lowered speed limits,” while the portions that had their speeds lowered did see an uptick in speeding violations.

Realistically speaking, raising the posted limits by a few miles per hour isn’t likely to shorten anyone’s commute by a meaningful amount. Traffic density is usually the deciding factor in how fast you’ll be able to go during rush hour and it’s unlikely you’ll be making any serious gains by bombing down the expressway a little quicker than your peers on your way into the office. You’d need to be going significantly faster than everyone else just to recoup enough time to swap out of your racing shoes after parking.

However, this changes the further away your desired destination happens to be. As someone who takes a lot of extended road trips, there is definitely time to be made by going faster than everyone else. Though you’ll still probably save the most minutes by making sure your pit stops are infrequent and don’t last very long. Otherwise, you’ll need to maintain a pace that’s well above the posted limits and likely to invite law enforcement to pull you over — undoing all that progress with a single traffic stop.

From AAA:

AAA recommends that changes in posted speed limits should consider a range of factors, including but not limited to the type of road, surrounding land use, and historical crash data. AAA supports automated speed enforcement, but programs must be carefully implemented to maintain community support, prioritize equity and consistently drive improved safety.

“The movement in statehouses to raise speed limits is happening across the country in at least eight states this year,” said Jennifer Ryan, director of state relations for AAA. “But the benefits are overrated, and the risks are understated. Increasing speed limits does not always yield the positive results envisioned by traffic planners.”

This study is the third phase of the AAA Foundation research examining the effect of posted speed limit changes on safety. In the Foundation’s first study, traffic engineers were asked how posted speed limits are set and what factors they consider in changing them. In the second phase, crash testing revealed that small speed increases have severe and potentially deadly effects on crash outcomes.

Nobody sane is going to claim that high-speed crashes are less deadly than their low-speed counterparts. Physics is pretty clear on the matter. But local and federal regulators are presently considering how best to rework roadways to improve safety and encourage alternative modes of transportation. The Biden administration even tasked the Department of Transportation to offer grants under the Bipartisan Infrastructure Law’s “Safe Streets and Roads for All” (SS4A) initiative.

Safe Streets mimics the older Vision Zero campaign to a large degree. It basically encourages cities to rethink their roads by embracing changes to roads that prioritize pedestrian and cyclist safety while also implementing lower speed limits for cars. The best aspects seem to find ways to physically separate automobiles from pathways taken by other forms of transportation. But critics aren’t too fond of seeing traffic lanes handover over to bicycles or an influx of speed bumps.

Additionally, Safe Streets embraces some of the advanced safety systems found in modern vehicles that even AAA has criticized as unreliable and automated enforcement measures (e.g. traffic cameras, sensors, etc) that have proven wildly unpopular with the public.

There are also questions about how effective these kinds of changes actually are. New York City implemented Vision Zero in 2014 by lowering speed limits and implementing more bike lanes. But local traffic deaths have fluctuated over the years. While overall traffic fatalities declined through 2018, they were already trending downward before the scheme was adopted.

Deaths have been tracking back upwards ever since, however. The good news is that pedestrian deaths seem to have come down overall. The bad news is that motorists and passengers seem to be dying at higher rates as cyclist fatalities fluctuate between years. Some of this may be attributable to the NYPD changing its policies to allow more high-speed pursuits. But it could be unrelated and the averages are being impacted by something else, as overall traffic injuries increased and didn't come down until 2020 when lockdowns kept everyone off the streets.

But we’ve already tried some of this before. In 1974, the federal government passed the National Maximum Speed Law, which restricted the maximum permissible vehicle speed limit to 55 miles per hour on all interstate roads in the United States. While often framed as a safety measure designed to tackle increasing automotive fatalities, it was actually done to help America cope with the 1973 oil embargo and subsequent gas shortages. The safety angle was tacked on after the fact.

The law was modified in the 1980s to allow up to 65 mph on certain roads and repealed in 1995 — once again allowing states to set their own speed limits. However, nobody seems to be able to agree on how much safer motorists actually became. Per capita roadway fatalities bounce around throughout its implementation and actually enjoyed a relatively steady decline after its was finally abolished.

It could be argued that the biggest improvements in safety are due to changes made regarding vehicle construction and technological advancements. This may also be true when we consider why per capita fatalities have increased since 2015. NYC has consistently attributed distracted driving as the #1 cause of accidents and 2015 is right around the time infotainment systems and smartphones became ubiquitous.

[Image: AAA]

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