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Single Slope Barrier for Bicycle Rail

Question
State MN
Description Text

A question has come up regarding the MnDOT Combination
Traffic/Bicycle Bridge Rail that MwRSF tested for MnDOT in 1998.  This
railing was tested as a “breakaway” railing mounted on a 32” tall J or F
barrier and passed for TL-4.  The link below is from your website and
provides more info regarding the railing and the test.



 https://mwrsf.unl.edu/reportresult.php?reportId=100&search-textbox=minnesota



 As you may know, MnDOT has now transitioned to using a 36”
tall single slope barrier with an 11 degree front face slope (example plan
sheet attached).  We also have standards for a 42” and 54” tall single
slope barrier, all meeting TL-4 NCHRP 350 (waiting for eligibility letter from
TTI and FHWA to approve as MASH barriers). The new barrier standard is used in
conjunction with the MGS 31” tall guardrail. 



The question is, can we use the combination
traffic/bicycle bridge rail mounted on the back of a 36” tall single slope
barrier and still refer to it as approved for TL-4 NCHRP 350?

Keywords
  • Bridge Rails
  • Permanent Concrete Barriers
Other Keywords Combination rail, pedestrian rail, bicycle rail
Date February 10, 2017
Attachment MnDOT Single Slope 36 inch barrier.pdf


Response
Response
A 32" tall, single slope concrete barrier has been successfully crash tested to the NCHRP report 350 safety criteria.  Increasing the height to 36" should not negatively affect the performance of the barrier, and may actually improve vehicle capture for the barrier by reducing the risk of heavy trucks rolling over the barrier.

Your 36" tall single single will also likely decrease the amount of contact/snag between an impacting vehicle and the steel rail components. The single-slopeed barrier is 4" taller, and 2" wider than the previous J barrier.  Additionally, if the bycicile rail is mounted at the same height relative to the ground, it will effectively be placed lower on the barrier compared to the previous (as tested) system.  All of these characteristics are likely to reduce vehicle contact with the steel rail components.

Thus, MwRSF would consider the placement of the steel tube bicycle rail on the backside of a 36" single-slope barrier as crashworthy to NCHRP Report 350 TL-4 standards.
Date February 10, 2017


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