Starting Jan. 26, 1998, the National Highway Traffic Safety Administration required trailer manufacturers to build all new trailers with energy-absorbing rear underride guards - what used to be called the ICC bumper. The new guards will make it nearly impossible for even a small car to underride the trailer in the event of a rear-end collision, while at the same time absorbing the energy of the impacting vehicle.
Until Oct. 1, there were no requirements for the trailer user to maintain the underride guards, even if they were bent or pushed in. But the new Section 393.86 of the federal motor carrier safety regulations adds a maintenance requirement.
To give fleets guidance, TMC recently completed a proposed new Recommended Practice 732(T). It will be voted on by mail ballot for approval this month. It is suggested in the RP that fleets need to be sure repairs don't change the energy-absorbing characteristics of the guard. Up to 3 inches' deflection is probably okay, but there are literally dozens of underride guard designs, and each design's energy-absorbing characteristics may vary. If bent in more than 3 inches, it should be repaired or replaced.
If either bumper end is bent upward, it must be bent back to the horizontal so as not to exceed 22 inches from the ground. Heat may not be used to accomplish this, as it could change the energy-absorption capabilities.
Some underride guards are welded on, others are bolted. Replacement pieces are usually available if it can't be bent back into position. You cannot arbitrarily put in pieces of your own design. They could change energy absorption.
Finally, each new underride guard comes with a NHTSA certification attached to the right-side crossmember, facing forward. If this cross piece is replaced, the label or plate from the old one should be transferred to the new one, or you can put on your own label containing the certification information.
Once RP 732 is approved, it will be available from TMC headquarters.