As licensed drivers, we're obligated to follow the posted speed limits, but have you ever wondered how those speed limits are determined?

According to the Maine DOT, speed limits in Maine (and many other states) are determined by the "85th Percentile Speed".  Basically, they measure the speed of 100 or more drivers traveling down a certain section of road during non-peak times.  They've found that 85% of drivers will travel at the same speed, regardless of the posted speed limit.  So, they use an approximation (+/- 3 MPH) of that speed to set (or reset) the posted speed.

This video explains it in further detail

In addition to the "85th percentile speed", when the Maine DOT  is setting a speed limit, they also look at the number of speed-related crashes, roadway features, traffic lights, intersections, whether the majority of traffic is local or "through", and the amount of on-street parking an area contains.