From David L. Roberson, Michigan Activist, National Motorists Association. 08/07/96
After pestering MDOT for about six weeks, Michigan NMA member Jim Walker was able to obtain relatively current speed data for Michigan--as reported by MDOT to the federal government for the 1994 - 95 fiscal year. For quite some time now I have been guessing (in the absence of any official documentation) that the 85th-percentile speed on Michigan interstates was about 74-mph. As you can see, I guessed low. The actual numbers given to us for the stated period are as follows:
Freeways posted at 65-mph: Average = 69-mph, 85th-percentile = 78-mph
Freeways posted at 55-mph: Average = 60-mph, 85th-percentile = 68-mph
Non-freeway routes posted at 55-mph: Average = 57-mph, 85th-percentile = 63-mph
MDOT was quite reluctant to release this information, perhaps fearing political consequences. This data lends particular irony to the current controversy over the 3-month "test" of a 70-mph limit in a few locations. Apparently, THAT limit would be 10-mph too low! Note that these numbers are marginally higher than those in the recent South Dakota speed survey AFTER they raised their speed limit to 75, and significantly higher than those reported by Montana where there are no daytime speed limits at all on many freeways.