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I wanted to get your opinions regarding the termination of the metal tube portion of the Texas HT railing (TXDOT drawing attached). We have a project where we will be using the HT railing on a bridge and using a 44” tall F-shape concrete barrier off both ends of the bridge, and we are developing ideas on how to transition between the two.

Please see the attached PDF. It presents 5 different options for transitioning from the Texas HT barrier (on the bridge) to Iowa’s 44-inch concrete barrier (off the bridge). Please provide your comments and/or recommendations regarding the use of each of the 5 options. Note that the top width of our 44-inch barrier is 8-1/2 inches.

Scott and I like the options which flare back onto the parapet at the same elevation. Option 5 may be easier to deal with considering it may use a smaller anchor plate on the back wall. To mitigate concerns for snag increased snag on the posts, it may be necessary to use a minimum tangent length of the tube prior to bending it back to the parapet. Let me know if you have additional questions regarding this matter. Thanks!

Thanks, Ron.  Just one point of clarification: the termination of the elliptical tube is a free end; it is not attached to the concrete.  Does this have any impact on your recommendation?

Do you know if the end that TXDOT uses was ever crash tested?  (it’s a free end as well)

I am not aware of any passenger vehicle crash tests being performed on the Texas HT bridge rail. I have contacted my colleagues at TTI to also inquire about any passenger vehicle crash tests on the original system as well as a similar rail on a vertical parapet where a lower rail was added. Based on this inquiry, both TTI and TxDOT have stated that no passenger vehicle crash tests were performed.

Could you share your opinion on the preferred treatment at the trailing end of a BR-27C bridge railing?  See both pages of the attachment.  Note that in some cases, the trailing end could lie within the clear zone of opposing traffic.

To begin with, I will assume that both the combination bridge rail and the concrete parapet are crashworthy.  The tapered/flared concrete end (proposed) is more desirable for downstream end impacts as the non-flared end (original) could potentially cause snag issues during vehicle redirection.  However, the flared end (proposed) is drawn such that it leaves the end of the rail open for potential snag issues for reverse direction hits.  As such, we recommend using the flared concrete end, but extending the rail to flared concrete end.  Thus, snag potential will be minimized for both directions of travel. 

A few notes on the design:

(1)    The concrete taper/flare should begin on the same plane as the face of the posts (or further back for a more conservative design.)  This flare depth will best minimize snag potential.

(2)    The flare/taper angle should be gradual / shallow enough to minimized snag. (i.e., 3:1 – 4:1)

(3)    There are benefits to bolting the rail to the concrete parapet to ensure stiffness and full lateral capacity.  However, if the concrete end is flared and the rail is extended to the flared and cut to match the slope of the flare, the free end of the rail would be supported laterally by the sloped face of the concrete parapet.  Thus, attaching the rail to the concrete is not necessary and the rail can remain free.

I realize I’m reviving an older question, but could you take a minute and review page 2 of the attached drawing?  Specifically, I’m curious if you would consider this design acceptable for both directions of travel (forward- and reverse-direction impacts).  The tube railing is cut to match the flare of the concrete with an approximate 1-inch gap between the two. 

Here’s another option for you to consider.

Both rail termination details you have included should perform well during impacts from either direction.   Having the free end of the rail cut with a flare to match the taper of the concrete parapet should minimize vehicle snag during impacts.  Also, the flared cut allows the rail to utilize the tapered concrete parapet as a lateral support to insure rail strength at this termination location (after a small lateral deflection the rail would be pressing against the concrete wall).  The short distance between the free end of the rail and the first post also helps insure strength at the end of the rail.