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A
ABS makes the combination stop in half the distance
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B
ABS prevents wheel lockup that would cause jackknife — for multi-trailer combinations, ABS on both tractor and each trailer prevents any individual unit from sliding sideways while another continues forward, dramatically reducing jackknife risk
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C
ABS is not permitted on multi-trailer combinations
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D
ABS only affects the tractor, not the trailers
Why this is the answer
ABS BENEFITS FOR DOUBLES AND TRIPLES are especially significant because the jackknife risk in multi-trailer combinations is higher than in single-trailer units. WITHOUT ABS: In a hard brake application on slippery pavement, wheels on any individual unit can lock; locked wheels provide no directional control (they can only push in the direction of existing momentum); if the dolly wheels lock while tractor wheels continue rolling, the dolly and second trailer can swing sideways — tractor jackknife; if tractor drive axles lock and the trailers continue pushing, the combination folds — tractor jackknife from behind; ABS PREVENTS LOCKUP: The computer cycles each wheel individually at 10-15 times per second; any wheel that begins to lock (lose traction) has pressure modulated to allow it to continue rolling; with all wheels rolling, each unit maintains directional stability during braking; the combination stays straight rather than jackknifing; LIMITATIONS: ABS does not shorten stopping distance significantly; it maintains control during maximum braking; the driver must still apply firm brake pressure — ABS modulates the pressure automatically; FEDERAL REQUIREMENT: ABS has been required on new trailers since 1998; most current CMVs have ABS on all axles including dolly; an ABS warning light that remains on after engine start indicates a fault that should be addressed before driving.
Source: FMCSA CDL Manual, Chapter 7, Doubles and Triples, ABS