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Transitioning 31

Question
State DC
Description Text I got the question below about transitions
between existing 27 inch high w-beam barriers and repairs made using 31 inch
high versions. The specific question below also asks about using a 27 inch
high terminal when the owner wants to use it to terminate a new 31 inch high
LON barrier.


1) Based on your MGS research and your vast experience with 27 inch high
barriers, is there an appropriate transition length over which you may
"safely" raise or lower w-beam rail by 3 inches? 1a) Assume all other
features are equal. 1b) Assume known differences like G4-1(S) transitioning
to MGS or vice-versa.

2) If an owner thinks they can save money by specifying a 27-inch high
w-beam terminal when using 31 inch high barriers, what is the "safe" place
to begin the 3-inch rise?

These questions assume the owner is basically satisfied with the performance
of 27-inch high barriers and or terminals but wants to begin moving to 31
inch systems whenever possible. If these are questions that should not be
trifled with unless crash tested, that, too, is an answer.
Keywords
  • End Treatments & Crash Cushions
  • Guardrail
Other Keywords none
Date June 24, 2009


Response
Response
See response below in red

I got the question below about transitions
between existing 27 inch high w-beam barriers and repairs made using 31 inch
high versions. The specific question below also asks about using a 27 inch
high terminal when the owner wants to use it to terminate a new 31 inch high
LON barrier.


1) Based on your MGS research and your vast experience with 27 inch high
barriers, is there an appropriate transition length over which you may
"safely" raise or lower w-beam rail by 3 inches? 1a) Assume all other
features are equal. 1b) Assume known differences like G4-1(S) transitioning
to MGS or vice-versa.
** For comparison purposes, I assume that you are referring to metric height
guardrail placed with a 27.75" top rail height. My best recommendation would
be to transition the 3.25" height differences over approximately 50 ft or
two 25-ft long sections of W-beam guardrail. With this reasonable grade
change, I am confident that there would not be any complications nor
degrading effects on the barrier's safety performance. Only increasing the
rail slope to 3.7 degrees should also allow for a relatively easy placement
of the eight splice bolts within the lapped joints.



2) If an owner thinks they can save money by specifying a 27-inch high
w-beam terminal when using 31 inch high barriers, what is the "safe" place
to begin the 3-inch rise?
** To be reasonable sure that the safety performance is not degraded and
without testing, I would "conservatively" recommend that the height
difference not begin until the end of the downstream end of the terminal is
reached.


These questions assume the owner is basically satisfied with the performance
of 27-inch high barriers and or terminals but wants to begin moving to 31
inch systems whenever possible. If these are questions that should not be
trifled with unless crash tested, that, too, is an answer.
Date April 4, 2012


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