South Dakota Speed Report

South Dakota's recent speed monitoring report (dated 5/28/96) shows the following numbers for the Interstates:

Average (50th percentile)65.6 mph65.466.266.068.3
85th percentile72.372.072.572.876.0

Yikes! Could it be? A speed limit set to the point where it is the safest possible speed, and furthermore, that most people aren't exceeding it?

Then there are the two-lane roads, once posted at 55, now 65:

Average (50th percentile)57.6 mph56.457.858.160.7
85th percentile63.862.463.864.468.6

Look at the 85th percentile numbers. When the limit was 55, people were going 7-9 mph over the limit. Now that it's 65, they're going 3 over. For the Interstates, the differences are less but still visible.

Here's something that makes you think. Note that South Dakota's speed-limited drivers are driving faster than the Montana drivers who have no speed limits. About 15% of South Dakota drivers exceed 75, but only 8% of Montana drivers do. Interesting, no?

Source: NMA's Web Page,

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