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Illinois Type TP-1 Railing

Question
State IL
Description Text

We worked together about a year ago regarding a bicycle railing attachment to an F-Shape parapet. I would appreciate your suggestions and direction on the attached Illinois Type TP-1 Railing.

We only allow this railing on Local projects (not State or Federal routes). Since it is mounted in conjunction with and on the back side of an 8” sidewalk with no barrier in front of it, it would be used for low speed applications (posted speed limit ≤ 45 mph) per AASHTO 13.4. We have it listed as a TL-2 barrier but I don’t have records that can verify this. Are railings mounted on the back side of raised sidewalks with posted speed limits ≤45 crash tested and evaluated for an AASHTO Test Level similar to railings in direct contact with traffic?

The height of the railing (42” above the sidewalk) satisfies the geometric height requirement of AASHTO Article 13.8 but the spacing of the railing elements does not satisfy the geometric opening requirements. We offer a concrete stub wall with a metal railing mounted on top that can be used for these applications but our County Engineers prefer to have an open steel railing. Do you see any possible recourse in salvaging this railing?

Thank you again for your suggestions and direction.      

Keywords
  • Bridge Rails
Other Keywords none
Date March 16, 2015
Attachment R-26.pdf


Response
Response

To answer your first question, sidewalk-mounted bridge railings have traditionally been crash tested and evaluated  in a similar manner to those mounted directly to concrete bridge decks. In fact, I have seen crash tests on several bridge railings that offered both non-sidewalk and sidewalk mounting options, and testing was performed on each variations. Further, some of these systems were even tested at lower performance/test levels. To my best recollection, there have been tests on all-steel beam and post systems as well as combination parapets with upper beam and post systems. In summary, these crash tests have occurred on bridge rails mounted on sidewalks and curbs at multiple test levels as well as on a variety of bridge rail types. Of course, many more tests have been performed on non-sidewalk-mounted bridge rails than sidewalk-mounted bridge rails.

 

With regard to the second question, I assume that the geometric opening requirements for which you are referencing is tied to the size of sphere that shall not pass as a function of elevation along the height of barrier. If that is the case, then one could consider modifications to add rails, modify rails, etc. Historically, there have been other guidelines for rail offset from post, opening size for snag mitigation, and rail location, as I recall. Those guidelines led to development of many steel beam and post railing systems over last 20 to 30 years. As a first step, we could investigate whether this particular design is nearly identical to any other crashworthy designs under AASHTO PL-1 & PL-2, NCHRP Report No. 350 TL-2, TL-3, & TL-4, or AASHTO MASH TL-2, TL-3, & TL-4. From that review, it may be possible to estimate whether or not the TP-1 system would likely be crashworthy based on prior testing. Is that what you would like us to do? Please let me know if further investigation is desired. Thanks!

 

Date March 17, 2015


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