How Are Speed Limits Set?

At the last Council meeting the City Council acted upon a request from our department to raise a speed limit.  I know that is unusual but we had been contacted by a person who works in the area of Harmon Road and who brought to our attention his belief that the speed limit did not comply with Public Act 85 of 2006 which sets the rules by which road authorities, including local officials, set speed limits. 

It is commonly believed that lower speeds are safer but that actually isn’t true.  Uneven speeds by drivers are  frequently crash causers.   I thought you might be interested in this video by the MDOT and the Michigan Sate Police which gives a short view on how speed limits are set. 

In the case of Harmon Road, we did a speed study which means that we measured the speeds of drivers in a 24 hour period and then calculated the speed that 85 % of drivers feel is safe to find what the limit should be.   The 85th percentile is a long standing engineering principle for setting speed limits. I think it makes good sense. 

And I believe that traffic enforcement is about crash reduction not revenue generation.  therefore speed limits and other traffic control devices should be fair and established in ways that aid traffic safety.

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I'm the Chief of Police for the Auburn Hills Police Department.