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I have a small question regarding Type C crash cushions.  Does there exist any MASH level crash testing data for these types of crash cushions being tested while attached to single sided guardrail runs?  An example would be having a bridge with rail posts and guardrail on the edges as opposed to a rigid parapet wall, then attaching a Type C onto the approaching end of the bridge guardrail rather than an end terminal. I know that this configuration sounds unorthodox but it’s one that has come in as a question from one of our internal designers.   

I am familiar with most of the crash cushion products that we use here in Missouri (TAU-M, QuadGuard, Delta) and with those, they are usually attached to (rigid) concrete barriers or double-sided rail runs that you would see in a median application.  The testing for those seems to have been done primarily against rigid barrier or with the use of a double sided rail application.  I haven’t seen any kind of MASH test data for applications that were transitioned down to a single sided rail.

Do you know of any such MASH testing for these types of cushions or is this something that we would not necessarily see as a practical application?  Any insight as always would be greatly appreciated.

Several manufacturers of crash cushions have provided details over time in their manuals for attachment of guardrail directly to the ends of a crash cushion. The attachment is usually based on existing approach guardrail configurations and consists of thrie beam guardrail and reduced post spacing to achieve a stiffness transition. I have seen other states implement these transitions, and I know for certain that Valtir and TrafFix have these options in their manuals.

That said, I am not certain how much crash testing has been done on these types of configurations. I do believe that they could be designed and tested to work safely, but one would need to consider similar behaviors that we design for in transitions to rigid bridge rails, including vehicle snag and transition between the different barrier geometries and stiffness over an adequate distance. Testing of these types of transitions to crash cushions would be desirable to verify their performance.

I lieu of testing, it would be desirable that guardrail attachments used with these devices follow the current state of the practice for approach guardrail transition design. This would provide for the highest level of confidence in their performance if they have not been crash tested. Design of the transition would likely be dependent on the specific crash cushion one is using. For example, the transition design would depend on the stiffness and geometry of the back end of the crash cushion, the side panels used in the crash cushion, and whether or not the system had an independent foundation or backup structure.

Let me know if that helps or if you wish to discuss the issue further. I would be happy to do so.

Thanks!