Speed and Impact

Traffic drives south on Highway 97 near the Cow Canyon Rest Area east of Shaniko on Oct. 20, 2018.

Nearly two years after speed limits were increased on highways in central and Eastern Oregon, a state-funded analysis shows that serious wrecks on those roads have gone up at a faster rate than places where the limit was unchanged.

Using four years of data on crashes across state highways and automatic traffic recorders to measure speeds, the Oregon Department of Transportation and Portland State University found that fatal crashes went up by 36 percent on highways raised to 70 miles per hour and rose 67 percent on roads that were increased to 65 miles per hour.

The Oregon Legislature voted to raise the speed limit on Interstate 84 from Ontario to The Dalles, Interstate 82 in Umatilla County, and Highway 95 in southeastern Oregon from 65 miles per hour to 70. Sections of Highway 395, Highway 97, and Highway 20 jumped from 55 to 65. The bill received bipartisan support in both chambers of the Legislature, was signed into law by Gov. Kate Brown and ODOT made the changes in March 2016.

Portland State’s study looked at the year following the speed limit increases, comparing it to data from the three years prior.

Chris Monsere, a PSU professor and the chair of the university’s civil and environmental engineering department, said he previously collaborated with ODOT on two different reviews on the literature surrounding speed limit increases.

Monsere and researchers Sirisha Kothuri and Jason Anderson found that speeding increased once the speed limits were relaxed.

In 70 mile per hour zones, vehicles traveling faster than 75 went up by 12 percent while drivers going past 85 went up by nearly 1 percent. In the 65 mile per hour zones, the most significant jump was in the percentage of vehicles going 65 or higher, which went up by 13.4 points.

In comparison, none of the control group highway segments had an increase in speeders above 2 percent, and there was virtually no increase in the number of cars traveling 85 miles per hour or higher.

Crashes were up on raised speed limit highways across-the-board, and in most cases, those increases were larger than the control segments.

Crashes that caused serious injury or deaths rose by 36 percent on 70 mile per hour roads, but that number also went up by 37 percent on control segment highways.

The real contrast was on 65 mile per hour zones, which saw a 67 percent increase compared with the 21-point increase seen on the control roads.

Despite the disparity in crashes between speed limit-increased roads and the control segments, traffic volume was only 10 percent higher in the speedier zones.

“These preliminary findings of the analysis are consistent with other related research and analysis that have found increased crash frequency and severity with increased speed limits,” the study states.

Studying ODOT data and Oregon State Police press releases, a November East Oregonian analysis found that fatalities from traffic crashes rose 10 percent in the 26 months after the speed limit increase as opposed to a 3.5 percent decline in traffic deaths statewide.

Barreto hadn’t read Portland State’s analysis and didn’t want to comment, but he previously defended it after the EO‘s analysis, saying he wanted to see how many crashes were attributed to drunk or distracted driving.

Given the variety of factors that could lead to a crash, Monsere said it’s difficult to determine cause of crash on a wide scale.

“You can think of a crash as having a random nature to it,” he said.

But he also reiterated that there’s a significant collection of research that shows that traffic collisions go up when speeds do.

Monsere said there’s other limitations to his analysis.

Ideally, the study would be able to look at three years of data after the speed limit increases went into effect instead of just one.

And since most of the well-traveled highways in Eastern Oregon already had their speed limits raised, he had to look at other parts of the state for control segments.

“They’re not ideal matches,” he said.

Monsere said he’d like to do a follow-up study not only with more crash data, but with more accurate speed readings as well.

While automatic traffic records are sparsely located on Eastern Oregon’s two-lane highways, Monsere said the next analysis would use new software that uses numerous GPS data points to more accurately measure speed and differentiate between car and semitruck.

In the meantime, ODOT is already taking some safety measures after PSU’s analysis.

Troy Costales, the ODOT Transportation and Employee Safety Division administrator, told the Oregon Transportation Commission at a Jan. 17 meeting that ODOT planned to continue to direct resources toward speed enforcement and could also install new signs and other infrastructure to prevent offroad and head-on crashes on two-lane roads.

In a Friday interview, Costales said the transportation commission is also starting a long-term discussion on establishing a process to change speed limits outside legislative acts.

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