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A crash cushion distributor for Trinity posed a couple of
questions to me regarding transitions for crash cushions.  I’ve copied
them below with my planned responses.  I don’t expect you to answer the
question specific to the Quadguard M10, just trying to understand current
requirements and past practice.  My questions to you are

• Does the MASH suite of tests include a transition to
  account for exposure to bi-directional traffic?


• If not, how have transitions for crash cushions been
  evaluated previously?


• If there aren’t standardized evaluation protocols, what
  should we be considering when a NCHRP350 transition is requested for a
  MASH compliant crash cushion?

Questions from the distributor

Is INDOT
going to require the MASH certification of transitions for crash cushions? I will need to get back to you.  Under NCHRP350 were the
transitions tested and certified?  Were the specifics included in the FHWA
eligibility letters under 350?

Can we
supply a NCHRP350 transition for a Quadguard M10?  I will need to get back to you.  The answer may depend
on the answer to the previous question.  Is it the opinion of the testing
facility that ran the M10 tests, that the NCHRP350 transition will perform
acceptably under MASH criteria?

I assume that you are referring to reverse direction impacts due to your reference to bi-directional traffic. Test no. 3-37 in  MASH is designed to deal with bi-direction traffic and reverse direction impacts on the crash cushion.

Test 37 examines the behavior of crash cushions and terminals during reverse-direction impacts.

This test is recommended for any safety feature that will be placed within the clear zone of opposing

traffic. This test involves a 2270P or 1100C vehicle striking the critical impact point (ClP) for reverse-

direction impacts. CIP locations for reverse direction impacts vary greatly from one system to

another and a generalized system for identifying these locations has yet to be developed. Note that the

configurations shown in Figure 2-3A for Test 37 are intended for illustration purposes only and do not

necessarily reflect the actual test configuration.

For most crash cushions with fender panels lapped against opposing traffic, the ClP should be selected

to maximize the risk of snagging on the end of the last fender panel lapped in this manner.

Many crash cushions attached to concrete barriers incorporate a tapered section between the wider

cushion and the narrower barrier face . Tn this situation, Test 37 should normally be configured to first

strike the barrier or the tapered section in order to maximize the potential for snagging. The 2270P will

generally be the critical vehicle for this test when a crash cushion is being evaluated.

For post-and-beam terminals utilizing a breakaway cable system, the 1100C will generally be the

critical vehicle for this test, and the impact point should be selected to maximize the risk of the vehicle

snagging on the anchor cable.

That test is currently divided into two potential tests (test 3-37a and 3-37b) using the 2270P and 1100C vehicles respectively. For your question, test 3-37a with the 2270P vehicle is required. Under NCHRP 350, many labs ran those tests in the reverse direction along the mid length of the crash cushion. Additionally, the NCHRP 350 test was at a lower (20 degree) angle. This was test no. 3-39 in NCHRP 350.

However, MASH specifies it differently by indicating that the test should be conducted upstream of the transition between systems and at 25 degrees. Note that it also notes that the CIP is device dependent. It may be that multiple test no. 3-37 would need to be conducted depending on the design.

SCI ran this test. See attached letter.

In terms of NCHRP 350 transitions, I am not sure what this would refer to in terms of attachment hardware as this test was may not have been conducted under NCHRP 350 or may have been conducted at a different impact location and impact conditions. I would be wary of applying NCHRP 350 crash cushion transitions that may or may not have been previously crash tested to a MASH device. 

Let me know if that answers your questions or if you would like to discuss it further.