Gov. Rick Snyder signed a package of bills that will require specified engineering standards in setting speed limits in Michigan, helping to put an end to what some motorists claim are speed traps. The changes went into effect when the governor signed them into law on Jan. 4. 

“This might be the best New Year’s present Michigan’s motorists and our visitors could have wished for,” said James Walker of the National Motorists Association, which supported the bills.

The bills will increase speed limits, with the limit on rural interstates going up to 75 mph. They also require that limits on roads be based on “speed studies,” in which traffic engineers observe how fast motorists drive on a given road. (The law makes exceptions for specific classes of roads such as neighborhood streets and roads in mobile home parks.)

The new law says that a speed limit can be no lower than the 50th percentile, or the speed exceeded by 50 percent of drivers. Speed limits can also be set based on a formula spelled out in the law, which is based on “access points,” or entrances on a given stretch of road. The formula is based on historic speed studies.

Traffic engineers use the 85th percentile to determine the safest speed, which can be done by eliminating speed variation among drivers. When a limit is set too low, the thinking goes, it encourages drivers to pick a variety of speeds, which could lead to tailgating, cutting-in and other conflicts that can cause crashes.

A number of groups, including those representing pedestrians, bicyclists and auto insurance companies, opposed making a speed standard part of state law, let alone setting it at the 85th percentile.

The Michigan Municipal League, which represents cities that set local speed limits, was pleased with the compromise.

“We believe it is important to be able to consider all users of the roadway when setting speed limits, and including the use of an engineering and safety study and having the flexibility to reduce speeds to the 50th percentile was a key factor in offering our support,” said John LaMacchia. He is the assistant director of state and federal affairs for the League.

While the National Motorist Association supported using the 85th percentile, Walker said the 50th percentile requirement should raise the limit in a number of places. He recently recorded the speeds of 1,193 drivers in Grand Rapids and found 97 percent of them exceeding the posted limit.

The law lets municipalities set lower limits, but only if the county road commission agrees. If there is no county road commission, the county board must agree.