Did lower speeds reduce crashes?
The number of vehicle crashes on Interstate 295 north of Portland took a noticeable dip in 2017 when the highway speed limit was reduced following a three-year period of escalating crashes.
State traffic engineers feel encouraged by last year’s numbers, but are wary to credit a lower speed limit alone for making the road safer, or declare the start of a downward trend.
“I like that the traffic and crashes are starting to go down, let’s hope it continues in the same vein,” said Steve Landry, head traffic engineer at the Maine Department of Transportation. “We need some more information, but we hope that what we have done will help solve the problem.”
Vehicle collisions, both serious and superficial, occur regularly on the 24-mile stretch of four-lane highway between Portland and Brunswick. Near-daily crashes can create notorious traffic jams that can turn an easy commute into a grueling slog, especially as the number of cars using the highway increases every year.
Speed is only one factor that can contribute to crashes, but the number of collisions on I-295 went up sharply after the state increased the speed limit to 70 mph almost four years ago, then showed a slight dip after limits went back down to 65 mph on the stretch last March. Weather, volume of traffic and the preponderance of distracted driving can also influence crash rates.
WAITING FOR A TREND
Vehicle collisions on I-295 between Portland and Brunswick rose 66 percent in the three years after 2014, when the state introduced higher speed limits on the highway. There were 290 crashes in 2016, compared to 174 in 2013, the last year before the speed limit was increased to 70 mph on highways statewide.
In 2017, there were 237 crashes on the stretch of I-295, an 18 percent dip from the previous year. Crashes dropped off after the speed limit was reduced in late March. In 2017, there were 162 crashes between March 27 and Dec. 31, compared to 227 crashes over the same period in 2016.
Lowering the speed limit was something the state could do immediately to address an obvious problem, Landry said. But without more evidence, he can’t say it was the most significant factor that changed things. The number of crashes on I-295 last year was still 36 percent higher than before the speed limit was increased.
“The high spike in crashes in 2016 might have been an anomaly,” Landry said. “Crashes can go up and down all over the place statewide. Until we start seeing a trend I can’t really say.”
Vehicle speed records on the highway from last summer indicate drivers are going just as fast as they did before the limit was reduced, with the vast majority of drivers going 78 mph or slower, according to Landry.
“There wasn’t a significant change,” he said.
CORRELATING SPEED AND CRASHES
New research from the National Transportation Safety Board questions whether the conventional approach to raising speed limits may contribute to crashes.
For decades, highway engineers have based speed limits on how fast the majority of drivers are going on a given road, calling it the “85th percentile,” reflecting that 85 percent of vehicles are driven at that speed or lower. Adjusting speed limits to reflect those actual road speeds results in postings that are “acceptable to the majority of motorists, but also fall within the speed range where the accident risk is the lowest,” according to the Maine DOT.
But the 85th percentile method is based on dated research, and may not actually be the point where the crash risk is the lowest, said Ivan Cheung, a transportation research analyst with the National Transportation Safety Board.
Instead, other factors like a highway’s crash history, characteristics and traffic patterns should be taken into account when determining speed, Cheung said.
“You have got to look at it more comprehensively, rather than letting how people drive determine what the speed limit is,” he said.
Increasing speed limits can also have the unintended consequence of encouraging faster driving, he added.
“If the speed limit is being raised, you are going to adjust to it,” Cheung said. “Over time, that creates pressure for the speed limit to continue to go up.”
LINK BETWEEN SPEED AND INJURY
According to a 2017 NTSB report, vehicle speed was a factor in 31 percent of all traffic fatalities nationwide from 2005 to 2014. While speed can increase the likelihood of a crash, there is a direct relationship between vehicle speed and injury in a crash, board researchers concluded.
“In general, increasing the top speed limit does increase the likelihood of getting into a crash,” Cheung said. “And that the crash will yield an injury is higher as the speed goes up.”
Speed limits have been steadily increasing in the U.S. after the federal government repealed its national maximum speed limit law in 1995. At that time, the top speed limit in most of the country was 65 mph. As of 2018, 41 states had speed limits of 70 mph or higher on some portion of their highways, according to the Insurance Institute for Highway Safety. Some Western states have top limits of 80 mph, and Texas has an 85 mph limit on some roads.
In 2011, Maine raised the speed limit to 75 mph on a lonely stretch of I-95 between Old Town and Houlton. Three years later, speeds on most of I-95 and I-295 and the Maine Turnpike were increased from 65 mph to 70 mph. The change doesn’t seem to have made a huge impact. According to Maine DOT crash data, there were 1,399 crashes in 70 mph speed zones in 2017, slightly under the 1,425 crashes in 65 mph zones in 2010, before Maine increased speed limits.
Speed has a critical, but underappreciated role in collisions, which is why the National Transportation Safety Board researched it, said Nathan Doble, another transportation analyst for the board. Recommendations from the report included implementing automated speed enforcement using radar and cameras.
“The topic of speeding doesn’t get as much attention as comparable issues like alcohol impairment,” he said.
CROWDED HIGHWAYS
Steadily increasing traffic volume on that 24-mile stretch of I-295 may help explain its frequent collisions.
In the past five years, traffic volume has increased an average of 9 percent. Its busiest point is near the Washington Avenue exit in Portland, which averages 87,790 vehicles a day, and the lowest volume is near the Route 1 connector in Brunswick, which averages 32,100 vehicles a day .
While the highway has not yet reached capacity, it can strain at peak morning and afternoon rush hours, particularly if there is a crash, Landry said. And more cars on the road increases the likelihood of more collisions.
“I think the closer you get to capacity, you are increasing potential conflicts out there. We are nowhere near capacity but we are closer than we were before,” Landry said.
Lt. Walter Grzyb, who commands Maine State Police Troop B, said his units have noticed lower speeds and fewer crashes on I-295, but also isn’t willing to conclude the reduced speed limit is the reason.
“Compared to a regular roadway, we certainly see more incidents of crashes,” Grzyb said. “I don’t think dropping the speed limit is going to change the character of the roadway, but it certainly has helped.”
State police have not adjusted policies or procedures to enforce speed limits on I-295, but as the most heavily trafficked route under its authority, “we definitely give it special attention,” Grzyb said.
Transportation department officials hope digital signposts installed along the highway that alert drivers to oncoming hazards have also helped reduce crashes. A growing awareness of the danger of distracted driving, especially using a cellphone behind the wheel, may also bring crashes down, Grzyb said. Distracted driving is blamed for the majority of crashes in Maine and the U.S., despite years of efforts to curb the practice.
“The awareness of distracted driving is becoming greater and greater all the time; maybe people are taking it to heart,” he said.
Road safety is emphasized in Maine’s updated three-year road plan, in an effort to bring down the number of crashes and collisions with pedestrians and cyclists. Last year was the deadliest since 2007, with 171 highway deaths and 21 killed walkers and cyclists, according to state figures.
A report on the 20-year future of I-295 is expected to come out later this year and will likely include recommendations such as pull-offs for law enforcement, variable speed limits and longer approaches and exit ramps, Landry said.
“The crashes are down; DOT is still pursuing fixes to keep that trending down,” he said.
Firefighters and police respond to an accident near Mile 17 of Interstate 295 in October 2016. There was an 18% drop in the number of crashes along a 24-mile stretch from 2016 to 2017, but authorities are loath to attribute the change solely to lowering the speed limit from 70 to 65 mph last March. (Brianna Soukup/Portland Press Herald)
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