Speed Limits and Lane Restrictions for LCVs
Long combination vehicles are subject to lower speed limits than standard CMVs in many states. Even in states where the general highway speed limit is 75 or 80 mph, LCVs — particularly triple trailer combinations — may be restricted to 55 or 60 mph. These reduced speed limits reflect the significantly greater stopping distances and the amplified jackknife and sway risks at higher speeds. Drivers must know the specific speed limits applicable to their configuration in each state traversed, as a speed that is legal for a standard semi is not necessarily legal for an LCV.
Lane restrictions for doubles and triples are common on multi-lane highways. Many states require LCVs to operate in the two rightmost lanes only (right lane and the lane immediately to its left) except when passing or making a left turn. Some states restrict LCVs to the right lane only on specified segments. Driving an LCV in the left lane (fast lane) or center lane on a three-lane highway when restrictions apply is a violation. These restrictions exist to reduce the risk of LCV-related accidents affecting through traffic and to improve traffic flow by keeping longer, slower-moving LCVs out of high-speed lanes.
Following distance for doubles and triples must be significantly greater than for standard singles. The crack-the-whip effect (described in the next chunk) means that a sudden hard braking application in a double or triple can cause rearward trailers to push forward or sway unpredictably. A following distance of 8–10 seconds at highway speeds provides the time necessary to apply brakes gradually and keep all trailer combinations under control. In adverse weather or on grades, even greater following distance is warranted.
At highway speeds, the aerodynamic interaction between trailers in a double or triple combination creates turbulence that can affect following vehicles and the stability of the trailers themselves. Crosswinds are particularly hazardous for high-sided doubles and triples because the rear trailer, having little resistance from connection rigidity, can sway laterally in gusts. Weather advisories for high wind conditions should be taken seriously by LCV operators, who may need to reduce speed well below the posted limit or stop operations when wind gusts exceed safe operating thresholds.