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. Further information can be found in Section 257.628. To lower or change a speed limit, a written request must be submitted to the Road Department. For more information please view the Setting Realistic Speed Limits (PDF) brochure by the Michigan State Police or the Establishing Realistic Speed Limits (PDF) brochure by the OHSP or view this video.
Myths & Realities
Myth Number 1: Speed limits significantly affect traffic speeds.
Myth Number 2: Most drivers travel too fast for road conditions.
Myth Number 3: Lower speed limits result in safer roads.
Myth Number 4: Lower speed limits allow for effective enforcement.
Reality Myth Number 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 Number 2: The majority of drivers travel at prudent speeds and are capable of recognizing driving conditions that require greater driving caution (i.e. slower speeds).
Reality Myth Number 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 Number 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.
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."