You are making up a set of doubles with one heavily loaded semitrailer and one light one. To handle as safely as possible once underway, where should the heavier trailer go?

Explanation

The more heavily loaded trailer belongs in the first position directly behind the tractor, with the lighter trailer at the rear. 49 CFR 383.115(b) names proper placement of the heaviest trailer as a required knowledge area for this endorsement, but the paragraph does not itself say which position is correct; the specific rule is driver-training guidance, attributed here to the manual rather than claimed as codified in that paragraph. Putting the heavy trailer at the rear works against the crack-the-whip effect, because the rear trailer already swings the most and stands the best chance of rolling over, so loading it down only adds to that risk instead of steadying the rig. Treating the two positions as interchangeable ignores that placement affects handling independently of each trailer being legally loaded, and the presence or absence of spring brakes on the dolly is a braking question with no bearing on which trailer should be heavier.

Source: 49 CFR 383.115(b)