Minnesota Cities Magazine
More from May-Jun 2018 issue

Letter of the Law: Slow Down—How Cities Change Speed Limits

By Amber Eisenschenk

With warmer weather in sight, more people will be out and about, and concerns about traffic may increase. Residents sometimes ask the city council to reduce speed limits in an effort to create a safer community.

The first step in seeking a change is to find out what entity maintains ownership over the street. It’s not uncommon to find interstates, state highways, county roads, city streets, and private association streets all within the same community. The authority that owns the particular roadway can make changes if necessary.

The most common speed limits regulated by state law where no special hazard exists are: 10 mph in alleys, 30 mph on streets in urban districts, 70 mph on rural interstate highways, 65 mph on urban interstate highways, 65 mph on expressways, and 55 mph on other roads. State law also has other suggested speed limits, but requires the controlling jurisdiction to affirmatively adopt them. A common example of this is a 25 mph speed limit on a residential street.

Process for change

To change a speed limit on a city street, the city council must have a traffic study performed and make a request to the commissioner of the Minnesota Department of Transportation (MnDOT) for approval. But since city speed limits tend to be pretty low, they aren’t typically the streets most residents are concerned about.

Authority to change the speed limits on county roads or state highways is vested with the counties and the state. The city can make a request to the county or state to reduce speeds and ask local law enforcement to be more visually present, but cities do not have the authority to make changes on their own.

When concerns about traffic on a roadway are brought to your attention, investigate who owns the roadway. For city streets, the council can determine that the speed limit should be changed, but should do so only after consulting with a traffic engineer.

Concerns about county roads should be given to the county department supervising the roads. For concerns about state roads, including the trunk highway system, contact the district traffic engineer at your MnDOT district office.

Considerations before changing

If a city requests a reduced speed on a state highway, MnDOT considers the following factors: road type and condition; location and type of access points (intersections, entrances, etc.); sufficient length of roadway (quarter-mile minimum); existing traffic control devices (signs, signals, etc.); crash history; traffic volume; sight distances (curve, hill, etc.); test drive results; and a speed study. Cities and counties should also consider these factors when changing the speed of roadways in their control.

During a traffic investigation by MnDOT, the speed study is a crucial step because it finds the speed that most drivers consider to be a reasonable speed during ideal road conditions. Traffic engineers perform radar checks of the roadway at selected locations, and this is the type of data collected in this study.

Traffic engineers then use the data results to determine the 85th percentile. The 85th percentile is the value indicating the speed at which 85 percent of drivers are traveling. MnDOT suggests that the posted speed limit should be near the 85th percentile as that is the maximum safe and reasonable speed for the roadway. This value, along with considerations of the other roadway factors, is how the traffic engineer reaches a recommended speed limit for the roadway.

Change may not equal desired results

Whether or not an analysis suggests that the roadway’s speed should be reduced, MnDOT warns that reducing speed limits often does not have the desired effect of reducing speeders. Studies show that roadway conditions have a greater impact on speed than the posted signs.

Lowering speed limits also has not been proven to lower the frequency of crashes as most are due to driver inattention. A posted speed limit that is too low can also cause crashes. This is because some drivers will follow the speed limits and others will not, which will cause a speed variation among drivers. That makes it difficult for drivers to respond appropriately to other vehicles. For example, it can be difficult for drivers to know when it is safe to pull out onto a roadway in front of other vehicles.

Other options

If speed limits cannot be changed, there are other tactics a city can use to make roads safer. “Traffic calming” is a term used to describe engineering approaches designed to slow drivers down.

The options usually involve changes to the city’s infrastructure of streets, sidewalks, curbs, signs, and traffic signals. Specific traffic calming techniques include the installation of speed bumps, raised intersections, roadway narrowing, and neighborhood traffic circles.

Amber Eisenschenk is a research attorney with the League of Minnesota Cities. Contact: aeisenschenk@lmc.org or (651) 281-1227.

Read the May-Jun 2018 issue of Minnesota Cities magazine

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