A spike that saw fatal crashes on Iowa’s highways exceed 400 in 2016 did not repeat itself last year, to the relief of authorities, but the number of deadly crashes in construction zones continued its troubling pace yet again — and drivers should expect to encounter more of them.

Only three times in the last decade has the proportion of fatal crashes within work zones exceeded 3 percent of the total. Two of those times were 2016 and 2017.

Mark Bortle, a traffic safety engineer with the Iowa Department of Transportation’s office of construction and materials, said the state’s nearly 3-year-old gas tax increase — which has pumped millions of dollars into additional road projects — could be a factor in the double-digit work zone fatalities seen in each of 2016 and 2017.

Map by John McGlothlen / The Gazette

“There are more dollars for us to spend on projects, so that does directly relate to more potential for drivers to drive through, around or past a construction project,” Bortle said. “There’s more projects out there and we’re doing more work on the higher volume roadways every year.”

The 10-cent per gallon increase has generated $515 million in additional revenue for road projects since it was passed in 2015, state data show.

What’s more, Bortle said, favorable weather extended last year’s construction season, which also increased the chances of motorists driving through work zones.

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Road construction zone deaths in Iowa reached 10 — or 3.03 percent of the total — last year, which is above the five-year, 10-year and 20-year averages, according to Iowa DOT data. Three of those 10 deaths were of road workers.

Work zone fatalities surpassed 3 percent of total Iowa highway deaths just two other times in the last decade — reaching 13 deaths or 3.23 percent in 2016, and 12 deaths or 3.08 percent, in 2010.

The Iowa DOT’s 511 traveler information website provides visitors with a snapshot of road conditions and work zones across the state, which can help drivers avoid construction areas altogether, Bortle said.

Last year’s drop to 330 total highway deaths — compared with 402 in 2016 — is a welcome return closer to the five-year average in Iowa, state officials said.

John McGlothlen / The Gazette

Yet the decline makes 2016’s spike, which followed a three-year downward trend, all the more puzzling, said Patrick Hoye, bureau chief with the Governor’s Traffic Safety Bureau.

“When we compare it to (2016), obviously we are feeling much better about the traffic fatality trend after 2017,” he said. “We really just are struggling to explain 2016.”

The Iowa Legislature last year sought to improve driving safety with measures that included expanding Iowa’s Move Over or Slow Down law and strengthening the ban on texting while driving, which may have helped lower the toll after they took effect.

The Move Over or Slow Down law requires motorists to change lanes if possible — or to slow down if not — to protect law enforcement and emergency crews, utility workers and road maintenance employees stopped by the side of highways.

The texting-while-driving law allows officers to pull over violators for that alone, without also having to spot some other offense, as was the case before.

Iowa State Patrol officers had issued 174 citations for use of electronic communication device while driving in 2016.

By late-December, 2017 had seen 668 such citations, Hoye said.

Warnings for texting while driving tripled in that span, from 129 in 2016 to 394 last year.

“That’s a significant jump in citations,” he said. “I think our other law enforcement partners would tell you the same, that their numbers would have increased throughout the year as well.”

An analysis of 2017 highway fatalities from Jan. 1 through mid-December — the most recent data sets available from the Iowa DOT — found that:

l The state’s most populated counties, Polk and Linn, topped the list with the most fatalities — 24 and 12, respectively.

l About 1 in every 4 fatalities involved impaired driving.

l A seat belt was not in use in approximately a third of the fatalities.

l Saturdays and Mondays were the deadliest days on Iowa’s highways, with a total of 47 and 46 deaths, respectively.

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The final tally of Iowa highway deaths is subject to change, as a fatality can be considered crash-related when a death occurs within 30 days after the crash, according to the Iowa DOT.

John McGlothlen / The Gazette

Jan Laaser-Webb, supervisor of transportation safety, utilities and access management with the Iowa DOT’s Office of Traffic and Safety, said impaired, distracted and drowsy driving remained key contributors to traffic fatalities in 2017.

Laaser-Webb said education and enforcement often are used to change drivers’ behaviors, but physical updates to the state’s roadways can have an impact as well.

Adding roundabouts in busy intersections, updating turn lanes and highway shoulders and repainting lane lines can help make roads safer, she said.

Looking to this year, Hoye said he expects debate at the Statehouse to possibly include strengthening ignition interlock rules for drunken drivers.

“With a combination of awareness and enforcement, we think we can change some of the driving behavior that was plaguing 2016,” Hoye said.

l Comments: (319) 339-3175; mitchell.schmidt@thegazette.com