By Ashley Tammen
Public Affairs Manager
Northcentral Kansas
|
When it comes to setting the speed limits in Kansas, “Increase
the speed” is often a statement we hear the most. As you may already know,
safety is a top priority for KDOT, and we look at many factors to determine a
safe speed for a road or highway. KDOT determines the speed limit of a roadway
through a speed study which may be conducted multiple times in a given year.
What
is a speed study?
A speed study is done using a radar gun to collect speed
data. Normally, this data is collected
during off-peak hours from about 50 random vehicles on a given roadway in each
direction at free flow speeds. The vehicles are selected at random to avoid
bias in the study results and the 85th percentile speed is the speed
at which 85% of the drivers are traveling at or below. The 85th
percentile speed reflects the safe speed as determined by a large majority of
drivers.
All
factors considered!
Many factors are considered in speed studies including crash
history, roadway geometry, activity within the driving environment, and
politics or state law. According to Brian Gower, Bureau Chief of KDOT’s Bureau
of Transportation Safety and Technology, one of the most important factors
considered in a speed study is engineering judgement from a traffic engineer. The
engineering judgment of a traffic engineer may determine, if any, of the
factors in a speed study warrant a downward adjustment of the 85th
percentile speeds.
Establishing
realistic speed limits
Often, speed studies may not result in a speed change as
this may not be the best decision for everyone such as the speed study
conducted in February 2016 of K-9 from Beloit to Clifton. Other times, only
sections of a roadway may result in a speed zone change like the speed study
conducted in May, 2015 of U.S. 81 and K-9 in Cloud County where it was
recommended only to raise the speed limit at State Street. Once all variables
are considered, a safe and reasonable speed limit is established for a given
road section.
Now that you’ve learned all this you may be wondering how we
determine when a speed study will be conducted or who initiates the request for
a speed study. Anybody can initiate a traffic study or check when the last one
was completed, simply contact your local KDOT office.
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