November 18


Curve warning The
Federal Highway Administration has decided to study a host of low cost safety devices
to determine whether they do in fact work.  Surprisingly, the effectiveness of many types
of warning signs has never been studied. 
The effectiveness of providing more conspicuous signing
and lane markings at roadway curves was recently analyzed in FHWA Publication Number


Crash data for horizontal curves on rural, two
lane roads was collected in Connecticut and Washington.  Connecticut has recently been upgrading their
existing curve warning signs to fluorescent yellow sheeting as well as adding fluorescent
yellow curve warning signs to locations that previously had no curve warning
signs.  Washington has recently focused
on installing more chevron curve delineation signs (type W1-8), either adding
chevrons to previously unsigned curves or adding more chevrons to previously
signed curves.  Crash data was collected
on roadways with the improved curve warning signs and compared with crash data
from similar roadways where the improved curve warning signs had not yet been

The most
significant safety improvements were related to crash reductions during dark
conditions and the reduction of injury plus fatal crashes.  Crashes on curves during dark conditions were
reduced by 35.3% in Connecticut and 24.5% in Washington.  Injury plus fatal crashes were reduced by 25.2%
in Connecticut and 18.0% in Washington. 
These findings were found to be significant at the 95-percent confidence
level, meaning there is a strong correlation in the statistical data between
installing curve warning signs and reducing these types of crashes. 

An economic
analysis was also done on improving curve delineations with warning signs.  It was found that installing curve warning
signs on rural, two lane roads is very cost effective with a benefit-cost ratio
exceeding 8:1.  A ratio of 2:1 or better
is typically considered a good investment. 
In short, improving curve warning signs is a very good idea.

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    Mike Spack

    My mission is to help traffic engineers, transportation planners, and other transportation professionals improve our world.

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