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 pass under or through a structure. Road clearance is
posted at the approach to a tunnel, underpass, bridge, or
other structure, or is marked on the structure itself.
The road clearance required for a vehicle is (a) the total
height of the vehicle and any part of the load which
may extend above the vehicle, (b) the total width of the
vehicle and any part of the load which may extend
beyond its sides, and (c) the free space required to
maneuver the vehicle and load. Usually, the word
CLEARANCE on a sign indicates distance from the road
to the overhead obstruction, while MAX WIDTH is used
for the space between obstructions at the sides or
between one side and oncoming traffic lanes.
a . Overall Height and Width. Determine the
overall height and width of the vehicle and load before
leaving on the trip. Be sure that the tires are inflated
properly before getting the height; if air is added to the
tires, the overall height may be increased. Be sure that
load tie-downs are properly secured; even if the load
cannot break loose, the overall width may be increased
if the load twists laterally on the truck. Write the
height and width of the vehicle on a pad or the driver's
log for reference during the trip.
b. Maneuverability.
I n addition to the actual
height and width, sufficient free space within specified
height and width limitations is required to compensate
for the constant up-and-down motion which occurs
w h i l e operating the vehicle; similarly, a constant
side-to-side compensation for sway is required. Both
the vertical and horizontal motion can be controlled by
reducing the vehicle speed. However, the driver should
allow several inches of free space for such maneuvering
when he compares his vehicle and load with the posted
clearance.
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