Dimensional and Weight Limits for
Unrestricted Highway Transport in All States
Gross Vehicle Weight
Tandem Axle Load
Maximizing the efficiency of the highway network requires that
vehicles and vehicular combinations be capable of unrestricted movement.
This movement is possible if vehicles or vehicular combinations
do not exceed legal size and weight limits imposed by the States
and the Federal Government.
Vehicles and vehicular combinations that exceed the legal highway
limits may require permits for highway transport. The difficulty
in obtaining these permits depends on the State's ploicy and the
amount that the legal permit is exceeded. Permits for vehicles that
exceed the legal width and length limits are not as difficult to
obtain as those for vehicles that exceed the legal height and weight
limits. Circuitous routing or time of day restrictions may be
required as a condition of the permit. Throughput delays may result.
In general, states may not issue permits for reducible or
divisible loads; however this may not apply to military vehicles
on the Interstate System.
DOD 4500.9-R Defense Transportation Regulation Part
III Mobility Appendix AV, explains the procedures for obtaining
The States and local government own and control all the roads
within their boundaries, including local, state, U.S., and Interstate
routes. They do not have to grant a permit if they feel the load
is too large or too heavy for safe transport.
Highway Bridge Gross Weight Formula
Axle spacing is as important as axle weight in bridge design.
A useful metaphor is thin ice on a pond. Walking on the ice concentrates
a person's weight on the small area covered by the person's feet,
therefore increasing the chance of the ice breaking and a very
cold dunking. Lying down on the ice, on the other hand, spreads
the same weight over a much larger area and decreases the chance
of the ice breaking.
In 1982, Federal highway law was amended to accept the following
bridge formula limits:
W = 500 (LN/(N-1) + 12N + 36)
Where: W = the maximum weight in pounds that can be carried on
a group of two or more axles to the nearest 500 pounds L = the distance
in feet between the outer axles of any two or more consecutive axles,
and N = the number of axles being considered. A vehicle that exceeds
the legal weight limits but meets the bridge formula is more likely
to obtain permits than a vehicle that exceeds both. The bridge formula
is incorporated into table 23 CFR 658. A sample problem for determining
bridge formula requirements can be found in Appendix A of MIL-STD-1366
Transportability Criteria (1.58 MB).
Many states are reluctant to grant highway permits for overweight
cargo vehicles with divisible loads since these vehicles can be
brought within normal legal limits simply by reducing the payload.
In some cases, a vehicle with a high empty weight may have a very
limited legal payload.
SDDCTEA has been very successful in easing Federal permit limitations
for movement of heavy DOD vehicle systems on public highways.
The definition of a nondivisible load was modified to allow "marked
military equipment or materiel" to be transported on the Interstate
System without the need for disassembly as long as State bridge
restrictions are not violated. Federal nondivisible restrictions,
which had been more limiting in many instances, are no longer applicable
to marked military loads and equipment. The actual rule change
can be found at the Federal
Register (28 K).
As an example of the potential significance of the change -- previously,
State transportation departments had to restrict movement of the
Palletized Load System (PLS) truck-trailer combination system to
a total weight of 80,000 pounds due to Federal nondivisible load
rules. This only allowed the combination to carry a total legal
load of 4.23 tons. With the change, States may now allow up to an
11.48 ton payload, which is determined by State bridge limits (this
is an increase of over 14,000 pounds of payload). Other vehicle
configurations will also benefit from the change.
However, one system that will not be able to take advantage
of this change is the Army's Heavy Equipment Transporter System
(HETS), which far exceeds all Federal and State gross weight and
axle load limits and has a much more complex movement process.
Certification as Essential to National Defense
Highway movement essential to national defense applies
to essential materiel that cannot be reduced in size or weight to
meet permit limits or cannot be moved by another transportation
mode. Training, maintenance, public relations mission, and
transportation savings are not valid justifications. The
Major Army Command (MACOM) Commander must certify that the load
is essential to national defense. The states have full authority
to refuse transport permission since they have absolute authority
over their public highways in both peacetime and wartime.