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Speed limits on state trunkline highways (I, M and US routes) are set jointly by MDOT and the Michigan State Police (MSP) in accordance with state law, which requires modified speed limits to be set based on traffic engineering practices and an objective analysis of the highway’s characteristics, as well as by the 85th percentile speed.

The 85th percentile speed is the speed at or below which 85 percent of traffic moves. State law allows setting speed limits below this percentile if an engineering and safety study shows a hazard to public safety not reflected by the 85th percentile speed; however, the law does not allow the speed limit to be set below the 50th percentile speed (speed at or below 50 percent of traffic moves).

If your community feels that a speed limit should be evaluated, the local municipality (city/village/township) may request through formal resolution that MDOT and MSP conduct an engineering and safety study, which would include an evaluation of current speeds. The resolution must state that the local municipality will abide by the decision made by MDOT and MSP based upon the results of the study.

Traffic signals are primarily installed to improve the efficiency of an intersection. Depending on the crash types, a signal may not address the concern and could inadvertently lead to more crashes.

Before determining whether or not a traffic signal is appropriate for a given intersection, MDOT must first perform a signal study and see if the location meets one or more of nine signal “warrants,” or conditions that must be met before a signal will be installed. Warrants include eight- and four-hour vehicle volumes, peak-hour volumes, pedestrian volumes, presence of a school crossing, presence of a coordinated signal system, crash experience, nearby roadway network traffic flow, and presence of a nearby at-grade railroad crossing. MDOT does not install traffic signals at locations that do not meet any of these warrants, as that may inadvertently increase the number or severity of crashes. 

MDOT does have rules for posting temporary political signs along state highways. These rules apply to state highways only; local road agencies and municipalities may have their own rules.

Generally speaking, our two biggest concerns are with safety and potential for littering. Signs are never allowed in locations where they impede drivers’ vision, or of a size and design that would pose a hazard if they were struck. Additionally, signs need to be removed within 10 days following elections so that they don’t become roadside litter or inhibit maintenance activities.

We don’t police signs based on content; we are focused on safety and littering. We post our rules expecting that most people will voluntarily comply. 

MDOT builds roundabout for several reasons, including:

• Safety: Roundabouts reduce vehicles speeds, as well as the number of conflict points. Roundabouts reduce head-on/left-turn and angle-type crashes that frequently result in serious or fatal injuries.
• Operations: With the use of yield signs instead of stop signs or traffic signals, vehicles can enter the roundabout when there are adequate gaps in the traffic flow. This reduces the number of vehicles that must stop and reduces the time vehicles are stopped. This reduces delay and increases the capacity of the intersection.
• Maintenance: Roundabouts reduce long-term operational and maintenance costs associated with traditional signalized intersections. There are no traffic signals to power and maintain, which can amount to a savings of about $5,000 per year.
• Aesthetics: Roundabouts create an area for community green space and landscape architecture. There are no large poles, overhead wires or signals to clutter the visual environment.

Refer to MDOT’s roundabouts web page for more information: Michigan.gov/Roundabout.

Lane reconfigurations, or road diets, can help improve safety for all roadway users by encouraging drivers to reduce speeds, removing congestion and reducing crashes related to left-turning vehicles by providing a center left-turn lane and providing space for other amenities, such as trails or sidewalks, wider shoulders, bike lanes, on-street parking or bus stop pull-offs. When properly placed, lane reconfigurations provide all of those improvements without significant delays or additional travel times.

The Federal Highway Administration (FHWA) has more information on road diets/roadway reconfiguration.