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Temporary Barrier Deflection Limits for Reduced Speeds

Question
State MO
Description Text

What is your opinion of reducing the deflection spacing behind
a temporary barrier, if the speed limit is marked at lower speeds than the
test speed of 62 mph?  Right now we are following the criteria from your
group in the deflection recommendation report of 45 inches unless used on
road ways with 10 foot lanes or greater and then we reduce the defleciton
to 24 inches.


Portable Barriers


Date August 26, 2004
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Response
Response
(active) 		The original Iowa temporary concrete barrier was crash tested to the TL-3 criteria of NCHRP Report No. 350. In that test, dynamic barrier deflections of approximately 45 in. were observed. Later, MwRSF published a report which stated that when the barrier is positioned near a bridge deck edge using the freestanding configuration, the clear distance between the deck edge and the back-side barrier base should be 45.3 in. However, for all other applications, the design deflection limit should be set at 600 mm or 24 in. This distance coresponds to the distance that the Iowa temporary barrier could be expected to deflect under the 85th percentile impact for passenger cars and light trucks. The 85th percentile impact condition was determined to be a 3/4-ton pickup truck impacting at a speed of 58 km/hr (36 mph) and 27.1 degrees.
Date August 31, 2004
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