Speed Limits

Please view the Setting Realistic Speed Limits brochure by the Michigan State Police or the Establishing Realistic Speed Limitsbrochure by the OHSP or view this video for more information

Speed limits are determined by either an engineering study to determine the 85 percentile speed or using what is sometimes called the "driveway formula" found in the 2006 amendment of Section 257.627 of the Michigan Motor Vehicle Code

The Michigan Motor Vehicle Code requires that drivers should, at all times, drive at "reasonable and proper" speeds, given the conditions. The law states:

"Any person driving a vehicle on a highway shall drive at a careful and prudent speed not greater than nor less than what is reasonable and proper, having due regard to the traffic, surface and width of the highway and of any other conditions; and no person shall drive any vehicle upon a highway at a speed greater than will permit him to bring it to a stop within the assured clear distance ahead."

Prima facie speed limits

The Michigan Vehicle Code sets speed limits for roads even where no speed limit is posted. These unposted speed limits are known as "prima facie" speed limits. The prima facie speed limits identified in the law are:
 

Residential and business streets: Where no speed limit is posted, the prima facia speed limit on paved or gravel platted residential streets and streets in business districts is 25 mph.
Parks: Unless a different speed is posted, the prima facie speed limit in parks is also 25 mph.
Highways: On highways outside of residential or business districts, if no speed limit is posted, the prima facie speed limit is 55 mph.

Non-prima facie speed limits

When the prima facie limit is considered too high on a county road, the State Police, in conjunction with the road commission and local township board, conduct a speed study to determine the "reasonable and proper" speed for the road.

Road agencies around the country have established standardized methods for conducting speed studies. These methods include engineering and traffic studies that examine such things as current traffic speed, traffic volume, accident rates, the character of the street (whether there are sidewalks, the number of driveways, sight obstructions, etc.), pedestrian activities and potential hazards that might not easily be detected by drivers.

In most cases, speed limits are based on the speed that the majority of the existing traffic is traveling. This is called the "85th percentile rule." This rule, which is used nationwide, dictates that whatever speed 85 percent of the traffic is traveling is the appropriate speed for the location under study.

The theory is that most drivers are responsible and will accurately judge on their own the proper speed for the conditions of the road.

Drivers slow down where there are curves and hills and/or other factors that might affect vehicle control or sight distance, and will go faster where the road is straight and level with no sight obstructions.

The 85th percentile rule is based on the following: It is generally agreed that with no traffic controls, the driver would adopt a reasonable speed for the prevailing conditions. Further, it is sometimes assumed that a certain percentage (usually 15 percent) of drivers will normally exceed a safe and reasonable speed.

To get an enforceable speed limit set or changed on a county road, it is necessary that the state police conduct a speed study and that the state police and the Road Commission concur on the speed limit. Unless the state police concur with the proposed speed limit, it is not legally enforceable.

Please contact our office if you have any additional questions.