Q – Why are speed limits being raised on some state highways and freeways?

A – Public Acts 445, 446, and 447 require MDOT and MSP to increase speed limits on 900 miles of non-freeways in Michigan to 65 mph, and on 600 miles of freeways to 75 mph, supported by speed, engineering and safety studies. The two agencies worked together to identify where these increases are safe and appropriate.


Q – How many miles of freeway and trunk line roadways will be affected by the speed limit increase?

A – According to MCL 257.627, speed limits shall be increased on a minimum of 600 miles of limited access freeway to 75 mph, and 900 miles of trunk line highway to 65 mph.


Q – How are routes being chosen for increased speed limits?

A – The new law requires that an engineering and safety review, as well as current speed data, support a higher speed limit in order for a speed limit to be raised. An engineering and safety review includes examining roadway features such as lane width, shoulder width, curvature, sight distance, number of access points and number of passing opportunities, as well as examining how a roadway is currently performing from a safety and operational perspective. The engineering and safety reviews, as well as current speed data, revealed routes that are best suited for a speed limit increase.


Q – How will I know what the speed limit is on a particular highway or freeway?

A – Routes with speed limits increased to 65 mph or 75 mph will have new speed limit signs posted. Information on routes with increased speed limits will also be posted online at www.michigan.gov/speedlimits.


Q – What about speed limits for trucks and school buses on freeways?

A – Speed limits for trucks and school buses on freeways have increased to 65 mph on freeways with posted speed limits of 65 mph or greater. This is a general speed limit change under Public Act 445, and is in effect regardless of currently posted truck/school bus speed limit signs.


Q – How much will these changes cost, both now and in the future?

A – It’s not clear yet, as costs are still being incurred with sign installation and associated work. Future costs will depend on what modifications are needed as part of future construction projects, which are awarded to the lowest bidder.


Q – How will these changes be paid for?

A – MDOT will use current maintenance funding (state funds) to pay for these initial changes. Future costs will likely be paid through a combination of state and federal construction funds.


Q – What other changes will be made to roads with increased speed limits?

A - Initial changes will include posting new or modified speed limit signs on affected routes, moving no-passing zone signs where applicable, installing new advisory speed limit signs where needed, and changing pavement markings to match modified no-passing zones and turning/passing lanes. Long-term, increased speed limits may prompt road design changes and modifications of other features, such as guardrails. MDOT and MSP focused on selecting routes that will be safe and appropriate based on current conditions, which will minimize the number of needed improvements.


Q – What is the 85th percentile speed, and why is it used to set speed limits?

A - State law dictates that MDOT and the Michigan State Police jointly set speed limits that are based on the 85th percentile speed, which is the speed at or below which 85 percent of drivers are currently driving a given section of roadway. For example, if 85 percent of drivers on a section of road are driving 55 mph or less, the 85th percentile speed would be 55.

Michigan uses this methodology because it is the national standard for setting speed limits, recognizing that the great majority of drivers instinctively drive at a speed that is safe and comfortable based on the roadway design and other factors. This also results in fewer conflicts between drivers, which lead to unsafe actions such as tailgating and improper passing.


Q – How will signs be updated?

A – Initially, many signs on freeways will have aluminum or plywood numbers applied over existing signs. Most signs on non-freeways will be removed and replaced with new signs. Old 55 mph signs removed during this process, if still meeting current safety standards, can be reused to replace damaged signs on other routes.


Q – How can I get my nearby state highway’s speed limit increased?

A – The process used by MDOT and MSP to identify routes where increased speed limits would be appropriate took into account current speed, engineering and safety reviews. This process is not based on requests for increased speed limits.


Q – What about speed limits on local roads?

A – Local roads are not under MDOT jurisdiction, so questions about local speed limit changes are best directed to the appropriate county road commission or municipality. Please refer to Public Acts 445, 446, 447, and 448 for information on changes to local road speed limits.



Q – How will this be enforced?

A – Traffic enforcement is handled by law enforcement. Law enforcement will continue to enforce the posted speed limit on all roadways.  Questions about enforcement on specific stretches of roadway should be referred to the law enforcement agency with jurisdiction over that roadway.


Q – How soon will these increased speed limits be in place?

A – MDOT and MSP are working to have some speed limit increases in place prior to mid-May 2017, and all changes required by the new laws in place prior to mid-November 2017.


Q – What about speed limits in towns along these routes with increased speed limits?

A – Reduced speed limits in communities along these corridors will remain in place.


Q – What about school zones?

A – Public Act 446 outlines how speed limits are to be determined in school zones. Primarily, the law limits speed limit reductions to 20 mph below posted speed limits, and limits the times of those reductions to maximum of 30 minutes before or after the regularly scheduled school hours. No speed limits can be reduced below 25 mph. This law also allows the school zone speed limit reduction for an off-campus lunch period, but does not apply to limited-access freeway nor highway with an overhead pedestrian walkway. State and local road agencies can designate a necessary school children crossing on a road with speed limit of 35 mph or more as a school zone, on the request of a school superintendent who has completed a school route plan. It also allows installation of louvered signs, digital message signs and flashing lights to supplement or replace required signs for school zones.


Q – With the speed limit increase on limited access freeways and trunk line roadways, will the speed of the motoring public also increase?

A – Historically, after changing a speed limit, the 85th percentile speed of the motoring public was not significantly affected. In some instances, the 85th percentile speed actually decreased.




Q – How does the speed limit increase affect speed enforcement by law enforcement? 

A – Law enforcement will continue to enforce the posted speed limit on all roadways. On roadways with an increased speed limit, motorists are expected to strictly adhere to the new speed limit on those roadways. Law enforcement will ensure motorists are complying with the newly established speed limits through high visibility enforcement.


Q – Since the speed limit is increasing, does this mean traffic crashes and fatalities will also increase?

A – The 85th percentile speed is a national scientifically proven method to determine and establish safe speed limits. Experience has demonstrated that 85 percent of drivers adhere to properly established speed limits which are reasonable, comfortable and safe for conditions. Following the speed limit increases, the MSP, in partnership with MDOT, will continue to watch crash data on these segments of road closely.