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Should Iowa change its interstate speed limit?

The science and safety of speed

Apr 21, 2017 at 5:30 am
    (Photo illustration: Cliff Jette/The Gazette)

    Driving across the newly constructed interstate system in a brightly colored Thunderbird before the days when cruise control was a common feature, an Iowan in the late 1950s and early 1960s could go up to 75 mph across Interstate 80 and I-35.

    Speed ahead to the mid-1970s, in the depths of the energy crisis, Iowans going on vacation in a classic station wagon on the interstate had to obey a federally controlled speed limit of 55 mph, established with the hopes of saving fuel.

    But with the power to regulate speed limits back in the hands of state governments, today’s Iowans can cross the state at 70 mph.

    Iowa’s current interstate speed limit is only 12 years old — the state Legislature raised it from 65 mph in 2005. Considering Iowa’s ever-changing speed limit history, coupled with recent legislation that could’ve raised the speed limit 75 mph and the slew of other states altering their limits, raises the question: Could or should Iowa change its interstate speed limit once again?


    Current Conditions


    Iowa ranks in the middle of the pack when it comes to rural interstate speed limits. Most states have speed limits that range from 65 to 80 mph, with Hawaii and Texas as outliers at 60 and 85 mph, respectively.

    Neighboring states such as Minnesota and Missouri, as well as a large portion of the eastern half of the country, all have 70 mph speed limits. However, states immediately to the west of Iowa — often with fewer people and larger expanses of open land — go with higher speed limits of 75 or 80 mph.

    For additional state speed limit conditions and exceptions, visit this map and table by the Insurance Institute for Highway Safety.

    In Kansas, where drivers can go 75 mph on rural interstates, “when it comes to setting speed limits, the goal is to post a speed limit that’s going to create the most uniformity in traffic,” said Steven Buckley, state highway safety engineer with the Kansas Department of Transportation.


    Iowa state Sen. Brad Zaun, R-Urbandale, recently introduced a bill in the state Legislature that would bring Iowa more in line with its western counterparts. The bill, which failed to be considered this session, would have increased the speed limit from 70 to 75 mph on Iowa’s rural interstates.

    Zaun said the inspiration for the bill came because he often travels throughout the United States and has seen how higher speed limits work.

    “It prompted me to look at and at least start the conversation about changing our speed limits,” Zaun said.

    Although it’s not his top priority, Zaun said he plans to pursue to bill in future legislative sessions, with the hopes of getting it heard by a subcommittee. He said he’s heard from a few of his constituents about the proposed change, with a majority of them supporting a higher limit.

    Zaun said that he spoke with DOT officials and learned that some of Iowa’s interstates were built to handle speeds faster than the current speed limit. The concept of “design speeds” for interstates might not be that simple, however.


    Design matters


    Tim Crouch, state traffic engineer with the Iowa DOT, said the interstates’ design speeds define how a number of features in the roadway are designed. He said the majority of interstates are designed for 70 mph, which affects the design of curves and the slope of ditches, among other things.

    “Over time, the design standards have changed since the interstate was first built, but the design speed has remained fairly consistent,” Crouch said.

    “We’ve made a lot of progress in making cars safer. On the other hand, we’ve made the roads less safe by raising speed limits.”

    - Russ Rader

    Senior vice president for communications, The Insurance Institute for Highway Safety


    When Iowa’s interstates were first built, the speed limit was 75 mph in the day and 65 mph at night, so the roads were built with roughly that design speed in mind. Even when the speed limit in the United States dropped to 55 mph, the design speed remained the same, Crouch said.

    State Sen. Wally Horn, D-Cedar Rapids, said he supported raising Iowa’s rural interstate speed limit to 75 mph and would in the future if the Iowa DOT said interstates were safe for that speed. He added that he’d endorse a study to examine what work would be needed to make Iowa’s roads safe for an increased speed.

    Horn added he spends a lot of time driving on Interstates 80 and 380. He said he travels around the speed limit but often gets passed by other drivers. The speed limit, he said, “should be at the level people would support and not exceed.”


    Parallels in the past


    The state of Iowa went through a similar debate before the Legislature voted to increase Iowa’s interstate speed limit to 70 mph, which took effect July 1, 2005.

    Since then, the DOT has put together a study on the safety impacts of that speed limit change.

    The study compared the average number of crash types from four years after the speed limit increase to data from the four years before the speed change — 2001 to 2004 — and also the previous 14 years — 1991 to 2004.

    The data showed the number of fatal crashes on interstate segments with the 70 mph speed limit increased more than 20 percent after the increase when compared to the 14-year data set.

    In the 14 years before the increase, Iowa averaged 20.8 fatal crashes per year on rural interstates. In the four years following the increase, the average number of fatal crashes on those stretches was 25.3 a year. 

    However, the increase is almost 30 percent when comparing the four years before the increase to the four years after. In the four years before the increase, the average number of fatal crashes was 19.5. After the increase, the average was 25.3.

    Story continues below chart

    Chart by John McGlothlen / The Gazette

    Before 1974 Iowa's interstates had a speed limit of 75 mph during the day and 65 mph during nighttime hours.
    Jan. 2, 1974 President Richard Nixon signed the Emergency Highway Energy Conservation Act, which required states to set a speed limit of 55 mph or face a loss of federal funding. The move was meant to reduce fuel consumption during the energy crisis of the 1970s.
    May 12, 1987 Iowa raises its interstate speed limit to 65 mph. In all, 41 states raised their speed limits in response to Congress' Surface Transportation and Uniform Relocation Assistance Act, which allowed a maximum rural highway speed limit of 65 mph.
    July 1, 2005 Iowa raises its interstate speed limit to 70 mph. Iowa was able to do this after 1995 when Congress passed the National Highway Designation Act, which relinquished federal controls over speed limits.
    February 20, 2017 State Senator Brad Zaun, R-Urbandale, introduced a bill that would have raised Iowa's interstate speed limit from 70 to 75 mph if passed and signed into law. The bill failed to be considered this session.

    Sources: Iowa DOT, American Journal of Public Health, the American Presidency Project, the National Museum of American History

    “While the increase in fatalities is tragic in terms of the additional five lives lost per year, the changes are similar to what might be expected from random variation in the data,” according to the report.

    Other categories examined in the study included serious crashes, or those involving a fatality or major injury, nighttime fatal crashes and nighttime serious crashes.

    The Insurance Institute for Highway Safety published a national study on increased speed limits. The organization estimated that in the period between 1993 and 2013, raised speed limits across the United States saw an additional 33,000 traffic deaths.

    “That’s just a staggering number,” Russ Rader, senior vice president for communications for the institute. “We’ve made a lot of progress in making cars safer. On the other hand, we’ve made the roads less safe by raising speed limits.”

    The institute, which is a research group funded by the auto insurance industry with the purpose of making roads safer and reducing crashes, accounted for other factors such as the number of young drivers and per capita alcohol consumption when calculating its statistics, according to the study.

    Russ said the institute expects traffic fatalities to increase about 8 percent on freeways and interstates after a state increases its rural interstate speed limit by 5 mph.

    “There’s no free lunch with this, and the cost is paid for in more crashes, more injuries and more deaths,” Rader said.


    Speed in the Sunflower State


    For an example of how a speed limit increase to 75 mph might affect a state, Iowa can look to Kansas.

    The Sunflower State increased its speed limits on some rural interstates to 75 mph in 2011.

    Kansas has roughly 10,000 miles of highway, and the speed limit was raised to 75 mph on only 353 miles, said Buckley, with the Kansas DOT.

    He said initial research into the three-and-a-half years before and after the change was significant enough that the DOT asked Kansas State University to do an in-depth analysis. Buckley hopes that work will be finished this summer.

    Kansas saw fatal crashes increase by 22 percent on those sections of rural interstates — from 86 to 105 — in those three-and-a-half years, even though deaths on the overall highway system dropped, from 746 to 706 in that time period.

    “That’s always something that we’re very conscious of,” said Brianna Landon, communications director with the Kansas DOT. She said the DOT uses social media and news releases to remind people of safe-driving practices.

    Buckley said, however, when a state raises its speed limit by 5 mph, it doesn’t necessarily mean people will drive 5 mph faster. The average speed, he said, may only increase 2 or 3 mph.

    “There’s a lot of drivers who aren’t comfortable driving that fast no matter what the speed limit is,” Buckley said.


    Science of Speed


    Predicting drivers’ behavior isn’t an exact science.

    Sgt. Nathan Ludwig, with the Iowa State Patrol, said drivers often go as fast as they need or want to go on Iowa’s interstates. And the speed travelers are comfortable driving at varies from person to person, he said.

    “Ninety percent of the time people are speeding because they’re running late...One person fails to plan ahead (and) they’ve put everybody else’s life in danger.”

    - Sgt. Nathan Ludwig

    Iowa State Patrol


    A 2011 survey on driving behavior and attitudes by the National Highway Traffic Safety Administration supports Ludwig’s observation, finding that “overall, people drive at approximately the speed that they perceive to be safe for the type of road that they are on.”

    Rural interstate highways, which already have the highest speed limits, may be the most common place for speeding, with Iowa State Patrol senior trooper Bob Conrad saying speeding is most likely to occur on flat, straight, open roads.

    What makes traveling at high speeds so dangerous is not just simply that cars are going faster. Total stopping distance, or reaction time combined with stopping distance, also is a factor for faster vehicles, which are covering more ground, Ludwig said.

    “If you raise your speed limits, you will see an increase in fatalities,” said Patrick Hoye, bureau chief with the Iowa Governor’s Traffic Safety Bureau, noting Kansas’ experience with increased fatalities after its speed limit change.

    Hoye, whose office is responsible for distributing federal funds to improve highway safety in Iowa, said the most common argument he hears for increasing the speed limit is that it may have economic advantages by allowing freight to move more quickly through the state.


    Speed of trucks


    Iowa’s trucking industry norms, however, may prevent trucks from going faster, no matter the speed limit.

    Brenda Neville, president of the Iowa Motor Truck Association, said trucking companies often regulate their drivers’ speed in an effort to be safer and more fuel-efficient.

    Many of the association’s member companies have put devices on their trucks that regulate speed, which often are set between 58 mph and 70 mph, Neville said.

    ... Even a slight improvement in fuel efficiency can impact the bottom line dramatically. So, overall, you are going to find that the majority of trucking companies take speed very seriously, from the CEO to the driver,” Neville said in a written statement.

    Buckley, with the Kanas DOT, confirms that point, saying trucks on rural Kansas interstates often don’t go more than 65 mph, which can be “problematic” when mixed in with faster cars on the road.

    Adds Neville: “I know that motorists sometimes get very frustrated when they get behind trucks on Interstate 80, and they are all set at the same speed, and congestion is created, and that can pose a safety threat. But, overall, the intent is to always maintain a safe speed and create an environment that is safe for everyone on the road, and that is paramount for most trucking companies.”


    Troopers, tickets and tragedy


    Roughly 70 percent of drivers are either considered speeders or sometime speeders, according to the National Highway Traffic Safety Administration’s behavior and attitudes survey. The survey considered driver’s answers to six behavior questions before classifying them as sometime speeders or nonspeeders.

    While the vast majority of survey respondents agreed that driving at or near the speed limit makes it easier to avoid dangerous situations, reduces the chance of an accident and uses less fuel, drivers still continue to speed on interstates. In all, 42 percent of survey respondents “agreed that driving at or near the speed limit makes it difficult to keep up with traffic.”

    In addition to speed enforcement, the Iowa State Patrol works to increase awareness among Iowans, in part, by posting speed radar readouts on Facebook, Ludwig said.

    The State Patrol sergeant said many Iowans are surprised to see how fast some drivers are going, as was the case with the Christmas Eve traveler clocked at 104 mph. The point of the patrol’s social media posts, he said, is to get drivers to realize how fast some people drive and to encourage them to slow down.


    “Ninety percent of the time people are speeding because they’re running late,” Ludwig said. “One person fails to plan ahead (and) they’ve put everybody else’s life in danger.”

    For Conrad, who has been a trooper for 26 years, high speeds all too often mean he must inform a family of a loved one’s death.

    “You want people to go home at the end of the day,” Conrad said. “I don’t think there is ever a death notification that I have forgotten.”

    Education, enforcement and engineering are often the ways to solve traffic safety issues, Conrad believes. But, for some reason, awareness campaigns about driving at excessive speeds haven’t had the same success in altering behavior as other campaigns, such as wearing seat belts or not smoking, Conrad said.

    Seat belt usage, for example, has increased from 11 percent in 1981 to nearly 85 percent in 2010, according to the federal Centers for Disease Control and Prevention. Smoking has decreased from 33.2 percent of adults in 1980 to 19.3 percent in 2010.

    Maybe the subject isn’t pushed as much in schools or maybe people test the limits with high speeds once and get away with it, he said. Or perhaps drivers believe high speed can be easily halted, with a tap on the brakes, Conrad said.

    Whatever the reason, the State Patrol plans to continue writing speeding tickets in hopes of convincing Iowa’s drivers to go slower on the interstates.

    Ludwig said reducing speeding is one of the patrol’s three major initiatives, with the other two being encouraging seat belt use and reducing instances of people driving while intoxicated.

    “You don’t realize how fragile things are, how quickly life can change,” Conrad said. “Anything that it takes to keep people alive is really what we should be doing.”

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    This story appears in the second edition of the Iowa Ideas magazine. Order a free copy here. 

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