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I have a question on Type A End Terminal placement that I need some expertise help with.  We have a situation where we are replacing a section of guardrail and a crashworthy end terminal on I-435 in Kansas City.  There is concrete barrier behind the guardrail.  The current guardrail runs parallel to the barrier approximately 20’ from the barrier with a Type A crashworthy end terminal.  We are wanting to flare the guardrail over towards the concrete barrier to prevent a vehicle from being able to go between the end terminal and the barrier.  I have included images below.  The red line is the proposed alignment of the new guardrail and Type A crashworthy end terminal, and the green line is the concrete traffic barrier. 

My question is what the required deflection distance between the Type A crashworthy end terminal and the concrete barrier would be (i.e. how close can we install the end terminal to the barrier).  It seems like if the space necessary behind the end terminal was more than the width of a vehicle then flaring it would essentially serve no purpose.  This question is one that I do not know testing history behind and any information that you have would be greatly appreciated.

This is not a situation we have addressed before, and there is limited data with which to answer the question. The

I believe there would be some concerns regarding flaring of the AGT back too close to the outer concrete parapet. In some impact conditions, the end terminal is allowed to gate or a vehicle impacting at an offset on the end of the terminal may rotate. Placement of the terminal closer to the parapet may limit the terminal’s ability to gate and/or could pin the gated terminal between the impacting vehicle and the parapet. Similarly, vehicles that rotate off the impact head to due to the impact angle or eccentricity may interact with the parapet while rotating, which could produce vehicle instability. These behaviors have not really been researched to date.

Alternatives could include extending the guardrail and end terminal farther upstream to limit the potential for a vehicle to get behind the terminal and reach the drop-off area. Another simpler alternative could be to install a sand barrel array between the guardrail and the concrete parapet prior to the drop-off to prevent errant vehicles from proceeding.

Let me know if that answers your question or if you wish to discuss further.