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Pier Protection

Question
State KS
Description Text

This is the location at which we discussed using a steeper flare rate to save room on the barrier width transition.  See attached PDFs. This is located in a rapidly developing area of Kansas City where traffic signals will be located about every ½ mile but the design speed will be 55 mph.  The 42" crash wall will be transitioned down to 32" tall and will be protected with a 69" Wide Quadguard.  As the drawing shows, there will be 450 mm (18") from the face of the 42" tall vertical crash wall to the bridge column.  Is this offset enough or does this encroach on the zone of intrusion?  The crash wall will be heavily reinforced and tied to the pavement.  The space between the crash walls will be filled with aggregate (gravel).  The thickness of the crash wall can be increased, if needed, but we prefer to provide as much shoulder as we can.  The design of the project is nearly completed.  If you have any questions, please let us know. 

Keywords
  • Permanent Concrete Barriers
Other Keywords none
Date March 6, 2006
Attachment barrier_plan.jpg
Attachment cross_section.jpg


Response
Response

An 18" ZOI distance with a 42 in. high barrier will meet TL-3.
Note that you don't have sufficient ZOI clearance for TL-4 or TL-5.
However, based upon your description of the roadway, I believe that TL-3 is appropriate. The rest of your installation, with the flared and tapered barrier appears to be reasonable.
However, you might consider writing a justification for using the steeper flare rate and put it in the file. I don't know whether exceeding the RDG nominal flare rate guidance for concrete barrier would necessitate an exception, but if it does, it should be easy to justify in this case.
Lengthening the barrier will increase crashes significantly without much reduction in severity for impacts in the flared region.

Date March 10, 2006


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