Malcolm Deighton, inventor of the SAPA rear underride guard, discusses how they tested their aluminum guard successfully at 35 mph and then at 40 mph.

You can see the 40 mph crash test at about 5:36 on this video:

Here is the engineering report on that crash testing: Sapa 40-30 RIG Test Engineering Report Version 1.3 (1)

Rear Underride Guard Facts:

1. The current federal standard for rear impact guards has specifications for preventing underride at impact speeds of 30 mph (though not requiring a crash test).
2. The proposed standard in limbo at NHTSA now would upgrade it to 35 mph to meet the Canadian standard (although most manufacturers are already meeting the Canadian standard). However, the NPRM and the Canadian standard do not require that the guards stop a vehicle for the full width of the guard. That’s what the IIHS has proven with their crash testing program.
3. The IIHS has tested the new designs of the 8 major trailer manufacturers and given them each a TOUGHGuard Award for being able to pass a crash test at 35 mph across the full width of the back of the trailer.
4. These stronger guards are being sold on new trailers — some as a standard feature and some as an Option.
5. There are retrofit kits which can be installed on existing trailers to provide TOUGHGuard quality underride protection at the rear of trailers. There have been very few of these sold — a mere drop in the bucket compared to the 11 million+ trailers on the road which have the older, too weak rear guards.
6. Additionally, Sapa Extrusions (now Hydro), an aluminum extrusion company, has designed an aluminum rear underride guard which has been successfully tested at 40 mph. Since this is now known to be possible, why would we not mandate a standard which would require this amount of protection at minimum?
7. The STOP Underrides! Bill calls for research to be completed to ascertain the outer limits of underride protection — so we know what level of protection can reasonably be required.
8. The STOP Underrides! Bill also calls for establishment of a Committee On Underride Protection to facilitate collaborative and effective discussion among all stakeholders.