What following distance should a doubles driver use compared to a single-trailer combination driver at the same highway speed?

FOLLOWING DISTANCE FOR DOUBLES AND TRIPLES must exceed the already-extended distances required for single-trailer CMVs for several reasons: BRAKE LAG — each additional trailer and dolly adds additional volume to the brake air system; when the driver presses the foot brake, air must travel to all units; the additional hose length and chamber volume in a doubles adds milliseconds to brake response compared to a single trailer; over highway distances this delay matters; TOTAL INERTIA — a doubles combination typically carries more total weight than a single trailer; greater mass requires more stopping force and distance; SYSTEM COMPLEXITY — more brake components means more potential for imbalance; if one unit's brakes are slightly weaker, the remaining units bear more stopping burden; CRASH SEVERITY — a doubles combination that rear-ends another vehicle has significantly more kinetic energy than a single-trailer; the consequences justify additional safety margin;

Minimum guidance: Apply the CDL's 1-second-per-10-feet rule and then ADD additional seconds for the complexity and length of the combination; many professional doubles operators use 6-8 seconds at highway speed where the formula would suggest 5 for a 50-foot tractor; in wet, foggy, or icy conditions, double again.