The purpose of a speed limit is to move traffic in a safe, yet fluid and consistent speed that is fitting with the surrounding areas.
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. To lower or change a speed limit, a written request must be submitted to the Road Commission. For more information 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.
Speed Limits - Myths & Realities
Myth #1: Speed limits significantly affect traffic speeds. (Reality)
Myth #2: Most drivers travel too fast for road conditions. (Reality)
Myth #3: Lower speed limits result in safer roads. (Reality)
Myth #4: Lower speed limits allow for effective enforcement. (Reality)
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
speed limit is posted. These unposted speed limits are known as "prima
facie" speed limits. The prima facie speed limits identified in the law
Non-prima facie speed limits
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.
Gravel Roads: Speed limits on gravel roads are not posted (unless in a platted subdivision) since conditions may vary widely from year to year. On gravel roads, if no speed limit is posted, the prima facie speed limit is 55 mph.
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.
Reality (Myth #1): Traffic speeds do not significantly change with the posting of a new or revised speed limit. Most drivers travel at speeds that they consider safe, regardless of the posted speed limit.
Reality (Myth #3): The more uniform the speeds of vehicles in a traffic stream, the less chance there is for conflict and crashes. Speed limits that reflect the normal actions of the reasonable majority, therefore, usually provide the most uniform speeds. In fact, unrealistically low speed limits may actually lead to crashes by producing two distinct groups of drivers - those attempting to observe the posted speed limit and those driving at what they feel is reasonable and prudent. These differences in speeds may result in increase crashes due to tailgating, improper passing, reckless driving and weaving from lane to lane.
Reality (Myth #4): Unrealistically low speed limits cannot be enforced with reasonable enforcement. In addition, they make the behavior of the majority unlawful and create public antagonism toward the police by creating "speed traps". However, realistic speed limits allow police to target those drivers clearly out of line with the normal flow of traffic.