Why should a combination vehicle driver increase following distance compared to a straight truck?

Combination vehicle drivers should increase FOLLOWING DISTANCE because the longer, heavier combination requires MORE distance and time to STOP, and the extra length/weight makes sudden maneuvers more dangerous (risk of skid/jackknife). CDL combination. FOLLOWING DISTANCE RULE: at least 1 SECOND for every 10 FEET of vehicle length at speeds under 40 mph; ADD 1 second for speeds over 40 mph. EXAMPLE: a 60-foot combination at 50 mph needs at least 6 + 1 = 7 seconds. Increase further in bad weather, on downgrades, and when heavily loaded. The longer stopping distance (plus air brake lag) means the driver must look far ahead and leave generous space. Knowing to increase following distance for combination vehicles (and the 1-second-per-10-feet rule) is commonly tested.