ST.PAUL, MN – The Minnesota Department of Transportation is increasing speeds on 5,240 miles of state highways – including nearly seven miles of Highway 25 between Highway 12 and the south side of Buffalo – based on the recommendations of a five-year study made available Wednesday. The speeds will increase from 55 to 60 mph.
All area highways were included in the study, with no increases recommended for Highway 25 between Watertown and Montrose or on Highway 12 anywhere east of Dassel.
Of the 7,000 miles studied, speed limits ultimately will be increased on 77 percent of rural, two-lane state highways, according to the final report. New speed limits go into effect once new speed limit signs are posted. Most of the signs posting the new speed limits are in place, with the rest expected to be up by spring 2019.
In 2014, the Minnesota Legislature mandated that MnDOT study all Minnesota two-lane roadways with a speed of 55 mph.
It is the most comprehensive study the agency has made in terms of miles studied and level of detail, according to Nathan Drews, engineering specialist in the Office of Traffic Engineering.
The study is also the largest system-wide change in Minnesota speed limits since the national maximum speed limit of 55 mph was included in President Nixon’s Emergency Highway Conservation Act bill in 1974. Later that year, the Minnesota Commissioner of Highways established an executive order about speed limits.
The $1.2 million study included collecting travel speed samples on each section of roadway and evaluating roadway geometrics and hazards to determine if a speed limit could be changed without affecting motorist safety.
The recommendation for a speed increase along each of these roadways considered the speed that 85 percent of motorists drive at or below, along with an evaluation of other factors; such as access points, shoulder width, vertical grades and crash history.
MnDOT has conducted before-and-after studies on many roadways that recently increased speed limits to 60 mph. There was no change in the overall 85th percentile speed from before the speed limit changes to after. The average speed of all drivers increased by 1 mph and the standard deviation, which is the measure of how spread out the drivers’ speeds were, reduced slightly.
“This means that, after speed limits increased, travel speeds at the locations sampled were slightly more consistent between each vehicle,” said Drews. “In other words, more drivers traveled at a similar speed after speed limits increased. This is a desirable outcome, but this change is very slight and may not affect the frequency or severity of crashes.”
This most recent study echoes results from the previous studies. From 2006 to 2013, MnDOT increased speeds to 60 mph on 1,550 miles of two-lane rural highways. Studies conducted to determine the impact of raising speed limits on those roadways found that the overall 85th percentile speed before and after the changes were the same, the average speed increased slightly and the variation of the speeds decreased.
According to Drews, a properly selected speed limit can potentially increase the safety of the roadway by creating uniform travel speeds for all vehicles.
MnDOT plans to study the effect of the changes over several years to ensure these roadways continue to operate safely.