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Raising the Speed Limit on Interstate 17 Is a Bad Idea

The Arizona Department of Transportation (DOT) is seeking the public’s input on determining an appropriate speed limit for I-17 “between the I-10 ‘Split’ interchange near Phoenix Sky Harbor International Airport and Peoria Avenue. The speed limit for that part of the I-17 is currently 55 mph.”

This call for input comes after the passage of SB1102, which regulates a minimum speed limit of 65 mph “on any interstate highway in counties with a population of 3 million or more people.” The publication notes that this area of Maricopa County has over four million residents.

SB1102 allows speed limits to be lower if:

  • The lower limit is deemed necessary by experts
  • The system capacity and mobility of the highway will not be reduced
  • The public gets an opportunity for input

The survey is open until September 30, 2023. You can also submit your feedback to A speed limit study by engineers is due to be completed in October.

Speeding-related accidents in Arizona

Put simply, speed kills. A recent car accident on I-17 took the life of a Phoenix woman after a speeding and impaired driver struck her car from the rear. Another crash caused by a speeding motorist killed a woman and injured another this past January.

The Arizona DOT reports that, in 2021, 426 people were killed and 20,069 injured in speed-related accidents. For driver violations, they report 34,639 drivers were cited for “speeding too fast for conditions” and 793 for “exceeded lawful speed.”

What do these numbers mean? They mean a lot of people are speeding, and the results are catastrophic or deadly. Raising the speed limit on I-17 can only contribute to more deadly car accidents.

Why higher speed limits are dangerous

Forbes reports that “41 states allow legal speeds of 70 mph or more, with the highest in the nation at 85 mph over State Highway 130 in Texas. According to the Insurance Institute for Highway Safety (IIHS), such boosts have been responsible for nearly 37,000 additional highway fatalities over a 25-year period.”

This makes sense – the higher the speed at the time of the accident, the more risk of fatal or catastrophic injuries. Researchers put together crash test dummy tests to see the difference, and found the following:

At 40 mph the test showed nominal intrusion into the passenger compartment, but at 50 mph the damage was much more severe, wrecking the driver’s-side door opening, dashboard and foot area. Increasing the speed to 56 mph caused even greater damage to both the vehicle and the driver, with the crash test dummy’s sensors indicating severe neck and lower leg injuries. At the two higher speeds, the upward movement of CR-V’s steering column caused the dummy’s head to go through the deployed airbag and smash against the wheel. Sensors indicated a high risk of fractures to the face and even severe brain injury.

Raising the Speed Limit on Interstate 17 Is a Bad Idea

Other research on speed limits shows that raising posted speed limits increases crash frequencies and rates. Lowering speed limits was associated with decreased crash frequencies. And, changes in travel times were small, whether the speed limit was raised or lowered.

Our roads are built for speeding

CNBC reports that speed-related crashes cost the United States over $40 billion each year, and that number doesn’t count the emotional toll of a serious car accident. Speed limits are created to cut down on the risk of car accidents, so why do they continue to happen at such alarming frequency?

“A lot of that is our culture, right?” said Zabe Bent, director of design at the National Association of City Transportation Officials. “We have a culture of basically driving and sort of trying to achieve the speed limit as a target rather than a limit.”

Jay Beeber, executive director at Safer Streets L.A., added, “People drive the way the road is built, that’s what happens. And doing anything else in terms of speed limits is just simply wasting your time.”

Smart Growth America notes that:

Roadway design has a strong impact on how people drive and is often more influential on driver behavior than the posted speed limit. While speed limit signs may only be posted every few blocks or miles, the road’s design is ever-present, continually providing guidance and visual cues. While there are myriad factors involved in these deaths, our streets are designed to move many cars quickly at the expense of safety for everyone who uses them.

In 2020, 60% of deaths occurred on non-interstate arterial highways, which are typically in urban and pedestrian-heavy areas. Researchers found that when streets are wide and straight, and intersections are rare or unsignaled, people feel comfortable driving faster, no matter what the posted speed limit.

What is the answer here? Says Charles Marohn, an engineer and founder of

Many of my engineering colleagues will reply that they, the engineers who design streets, don’t control the speed at which people drive and that speeding is an enforcement issue. Such an assertion should be professional malpractice. It selectively denies both what engineers know and how they act on that knowledge. For example, professional engineers understand how to design for high speeds. When building a high-speed roadway, the engineer will design wider lanes, more sweeping curves, wider recovery areas and broader clear zones than they will on lower-speed roadways. There is a clear design objective (high speed) and a professional understanding of how to achieve it safely.

There is rarely any acknowledgement of the opposite, however: that slow traffic speeds can be obtained by narrowing lanes, creating tighter curves, and reducing or eliminating clear zones. High speeds are a design issue, but low speeds are an enforcement issue.

Until our roads have better and safer designs, it is important to always drive according to posted speed limits.

Were you or someone you love injured in a car accident caused by speeding? Talk to the skilled injury attorneys at Plattner Verderame, PC today. We can put our years of experience to work for you, working to secure compensation for your injuries, losses, and damages. To schedule a free initial consultation about your accident, fill out our contact page or call our Phoenix or Tempe offices. We are here to help.