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Surfaces leading to an impact attenuator.  I see they should be 10:1 slopes or flatter but the surface type, is grass or compacted aggregate an acceptable surface?  I know we have done this in the past but just thought I should ask before we start giving direction to do this.  Or does it depend on the unit?  I was reading about the Smart Cushion and they only talk about the material for the pad that the unit sits on. For the slopes in front of and beside the unit, the material is not mentioned.

Is this something you could help me with? 

We would agree on the 10:1 or flatter approach slopes. We have provided similar guidance previous for guardrail and have noted that it would be reasonable for crash cushions and terminals as well.

We believe that the surface adjacent to the barrier could be paved or an unpaved vegetation, compacted aggregate, or other consistent surface. Loose soil or other similar unfinished surfaces may provide for inconstant traversal and vehicle trajectory prior to impacting the device. We have run many crash tests traversing compacted aggregate on the approach to barrier systems without issue. Thus, we do not believe that there would be a need to pave all the way to the attenuator. I would note that one would want the surface to be fairly level with the mounting pad to eliminate the potential for a significant lip that the vehicle must traverse.

There may be some advantage to doing so, as a paved surface could provide improved steering and braking prior to impact, but it would not be required.

Thanks!