Reference · Terminology
Glossary
The vocabulary of US trucking regulation, in plain language. Where a term is defined or fixed by statute, the governing citation is shown beside it; where it is ordinary industry usage rather than a legal definition, no citation is given rather than an invented one.
26 terms · A to Z
A
Air-mile radiusA straight-line distance from the driver’s reporting location, not road miles. Several hours-of-service exceptions are drawn on air miles, so the qualifying area is larger than a road-mile figure suggests.
Axle groupTwo or more axles close enough together that the law treats their combined weight as one limit rather than summing individual axle limits.
B
Bridge formulaA calculation relating the weight carried on a group of axles to the distance between them. It can restrict a vehicle below the flat axle maximums, so meeting the single and tandem limits is not sufficient on its own.
C
CDLCommercial driver’s licence. A driver may hold only one, and the disqualification periods attached to it are federal — states administer the licence but may not fall below the federal floor.49 CFR § 383.51
CMVCommercial motor vehicle. The threshold definitions determine which federal rules apply at all, and they vary between the safety regulations and the licensing regulations.
D
DisqualificationA period during which a driver may not operate a CMV. A first major offence draws one year, or three years if the vehicle carried placarded hazardous materials; a second, in a separate incident, draws life.49 CFR § 383.51(b)
E
ECMEngine control module — the truck’s engine computer. An electronic logging device must link to it, which is why a phone alone cannot satisfy the ELD mandate.
ELDElectronic logging device. Hardware or software integrally synchronised with the engine that records driving time automatically, replacing paper logs. It is not a GPS tracker.
Em dash (—)On this site, an em dash means no verified primary source. It never means zero, and it is never a neighbouring jurisdiction’s figure carried across.
Escort / pilot carA vehicle accompanying an oversize load. Thresholds, equipment and certification requirements are set by each state and are not federally harmonised.
F
Frost lawA seasonal reduction in permitted axle weights during spring thaw, when saturated subgrade makes pavement vulnerable. Applies in northern states and is posted by route.
G
Grandfathered exceptionA weight or dimension allowance a state held before federal standardisation and was permitted to keep, which is why some Interstate segments carry limits above the usual federal figure.
Gross vehicle weightThe total weight of the vehicle, its load, fuel, driver and equipment — not the cargo weight alone.
H
HOSHours of service. Federal limits on driving time: ten consecutive hours off duty before driving, no driving after the fourteenth consecutive hour on duty, and eleven hours of driving within that window.49 CFR § 395.3(a)
I
IFTAInternational Fuel Tax Agreement. A quarterly return apportioning fuel tax between jurisdictions by miles driven in each, filed even when no travel occurred.
Interstate vs intrastateWhether the carriage crosses a state line, or is part of a journey that does. Interstate operation triggers federal jurisdiction; purely intrastate operation is governed primarily by state rules.
L
Legal widthOn the National Network, 102 inches. Unusually the rule is a ceiling and a floor at once — a state may impose neither more nor less — with Hawaii permitted to keep a 108-inch maximum.23 CFR § 658.15(a)
N
National NetworkThe system of highways on which the federal size and weight standards apply, comprising the Interstate System plus designated additional routes.
Non-divisible loadA load that cannot be separated into smaller units without unreasonable cost, damage or destruction. Only non-divisible loads normally qualify for an oversize or overweight permit.
O
Oversize / overweight (OS/OW)A load exceeding legal dimensions or weight, requiring a permit. Federal law grants states the power to issue such permits; the thresholds and fees are state law.23 CFR § 658.15(c)
P
Placarded hazardous materialsHazardous cargo at quantities requiring warning placards. Carrying it raises several penalties — notably tripling a first CDL disqualification from one year to three.49 CFR § 383.51(b)
Primary sourceThe document that establishes a rule — the statute, regulation or official agency publication itself, rather than a summary, mirror or secondary reproduction of it.
S
Single axleOne axle, or axles spaced closely enough to be treated as one, assessed against a single weight maximum.
Split sleeper berthDividing required off-duty time into two qualifying periods rather than one continuous block, so that neither period counts against the driving window.
T
Tandem axleTwo axles spaced within a defined distance and assessed as a group. It is the axle configuration most often decisive in practice, and the figure that varies most between states.
ToleranceA margin above the posted limit that enforcement will not cite. It is not an increase in the legal limit and is not uniform between jurisdictions.