Heavy Haul Glossary: Key Terms Every Shipper Should Know

Heavy haul trucking has its own vocabulary — terms that carriers, permit agencies, and equipment operators use routinely, but that shippers encountering oversize freight for the first time often have to look up mid-conversation. This glossary covers the most important terms you will encounter when booking an oversize or overweight load, reviewing a permit document, or discussing route planning with your carrier.

R&RM LLC has been moving oversize loads and overweight loads since 2011. The definitions here reflect how these terms are actually used in practice — by carriers, state DOTs, and FMCSA enforcement — not just dictionary definitions.

A

Allowable Axle Weight

The maximum legal weight permitted on a single axle or axle group, as determined by federal law and state DOT rules. Federal law sets the standard axle limit at 20,000 pounds per single axle and 34,000 pounds per tandem axle group. States may set lower limits on certain roads or bridges. Overweight permits authorize axle weights above these limits for specific routes.

All-Terrain Crane

A mobile crane mounted on a multi-axle road-legal carrier, combining the on-road mobility of a truck crane with the off-road capability of a crawler crane. All-terrain cranes can drive from job site to job site under their own power for short moves but are typically transported on lowboy trailers for long-distance relocations. Common examples include Liebherr LTM series and Grove GMK series cranes. See also: crane transport.

Annual Permit

A permit issued by some states that allows multiple oversize moves throughout the year, within defined dimension limits, without requiring a separate trip permit for each move. Annual permits typically cover loads up to a certain width or weight threshold. Loads that exceed those thresholds still require trip permits even if the carrier holds an annual permit for smaller loads.

Axle Spacing

The distance between axle centerlines on a vehicle or trailer. Axle spacing is a key factor in bridge formula calculations — a wider spread of weight across more axles and greater distances reduces the stress on any single bridge span. Permit engineers analyze axle spacing when evaluating whether a load can cross specific bridges without causing structural damage.

B

Blocking and Cribbing

Wood or composite materials placed between the load and the trailer deck — or supporting the load from below — to prevent movement, distribute weight, and protect the load surface. Blocking runs lengthwise against the load to prevent side movement; cribbing stacks horizontally under the load to raise it and distribute point loads across a wider deck area. Proper blocking and cribbing is an FMCSA requirement for most heavy equipment transport. See also: load securement for heavy haul.

Booster Axle

An additional axle added to the rear of a trailer to increase the number of axles distributing the load weight, reducing per-axle weights to stay within legal limits. Booster axles can be fixed or retractable (raised when not needed). On very heavy loads, multiple booster axles may be required to get per-axle weights under the permit thresholds for each state on the route.

Bridge Formula

The federal formula — codified at 23 U.S.C. § 127 — that determines the maximum weight a vehicle combination can carry on any set of consecutive axles, based on the number of axles and the distance between the outermost axles in the group. The bridge formula sets the effective weight limit for most heavy haul loads even on corridors where the gross vehicle weight permit allows a higher total. A load that appears legal by total GVW may still violate the bridge formula if axles are spaced too closely. See our guide on the bridge formula and weight limits.

Bridge Rating

An engineering assessment of the maximum load a bridge can safely carry, expressed in tons or pounds. Bridge ratings are maintained by state DOTs and updated based on structural inspections. When an oversize load's permit route includes a bridge with a low rating relative to the load's axle weights, the carrier may need to submit engineering calculations or use an alternate crossing. Some states require bridge analysis documentation as part of the permit application for very heavy loads.

C

Cargo Securement

The system of chains, straps, binders, blocking, and dunnage used to prevent the load from moving during transport. FMCSA Part 393 sets minimum cargo securement standards for commercial vehicles — including working load limit requirements for tie-downs and equipment-specific rules for heavy machinery like bulldozers, cranes, and generators. See our guide on load securement for heavy haul equipment.

Counterweight

Ballast attached to the rear of a crane superstructure to offset the weight of the boom and load during lifting operations. Counterweights are typically the heaviest removable component of a crane and are routinely detached for transport to reduce the transport weight of the crane carrier and redistribute weight across the trailer axles. Counterweight packages are transported separately on flatbeds or lowboys alongside the main crane.

Crane Carrier

The self-propelled road vehicle that forms the base of a mobile crane — distinct from the superstructure (upper works) and boom. For transport, the crane carrier is typically driven onto or loaded onto a lowboy trailer, while the boom and counterweights are transported separately.

Crawler Crane

A crane mounted on tracks rather than rubber tires, offering high stability and capacity for stationary lifting but requiring transport by trailer for all moves between sites. Crawler cranes are disassembled — boom sections removed, counterweights separated, tracks sometimes retracted or removed — before loading onto a lowboy trailer. See also: crane transport.

D

Daylight-Only Movement

A permit restriction specifying that the oversize load may only travel between sunrise and sunset. Most states impose daylight-only restrictions on loads above certain width or height thresholds. Night movement may be permitted under some circumstances with additional lighting requirements and specific permit authorization, but it is the exception rather than the rule for most oversize loads.

Detachable Gooseneck

See RGN (Removable Gooseneck).

Dispatch

The carrier's operational coordination function — the team or person managing driver assignments, route execution, permit compliance, and in-transit problem resolution. On complex heavy haul moves, dispatch is the primary point of contact for the shipper and the driver throughout the transit. R&RM LLC maintains 24/7 dispatch contact on all active moves.

DOT

Department of Transportation — used to refer to either the federal U.S. Department of Transportation or an individual state's department of transportation (e.g., Georgia DOT, Texas DOT). State DOTs issue oversize and overweight permits, set the legal dimension limits for loads on state-maintained roads, and conduct roadside enforcement of permit compliance. The federal DOT — through the Federal Highway Administration (FHWA) and the Federal Motor Carrier Safety Administration (FMCSA) — sets the baseline federal standards that state DOTs must meet or exceed.

Drive-On Loading

A method of loading self-propelled equipment onto an RGN trailer by driving the machine forward over the detached gooseneck and onto the trailer deck. Drive-on loading eliminates the need for a separate crane or forklift at the origin site and is the most common loading method for wheeled or tracked machines that can move under their own power. See also: RGN hauling.

E

Escort Vehicle

See Pilot Car.

Extendable Trailer

A trailer whose deck length can be adjusted by pulling a sliding section outward, allowing the trailer to accommodate loads of varying lengths. Extendable trailers are common for long steel beams, bridge girders, and wind turbine components. When extended, the overall combination length may exceed standard legal limits and require an oversize length permit.

F

FHWA

Federal Highway Administration — the federal agency within the U.S. Department of Transportation that oversees the Interstate Highway System and establishes federal weight and dimension standards. FHWA administers the federal bridge formula and the gross vehicle weight limits that apply on the Interstate System. States set their own limits on non-Interstate roads, which may be lower than the federal maximums.

FMCSA

Federal Motor Carrier Safety Administration — the federal agency within the U.S. Department of Transportation that regulates commercial motor vehicle safety. FMCSA issues the regulations covering hours of service (HOS), driver qualifications, vehicle inspections, cargo securement (Part 393), and carrier safety ratings. FMCSA does not issue oversize permits — that is a state DOT function — but FMCSA regulations apply to all commercial carriers including those operating under state oversize permits.

Flag Car

See Pilot Car.

Flatbed Trailer

An open trailer with a flat deck and no sides or roof, used for loads that can be loaded from the side, top, or rear using a crane or forklift. Standard flatbeds have a deck height of approximately 5 feet from the ground, which limits the usable height for tall loads. For heavy equipment transport, flatbeds are typically used for dismantled components — boom sections, counterweights, attachments — rather than for the main equipment body, which usually requires a lower-deck trailer. See our guide on RGN vs flatbed trailers.

G

Gooseneck

The front section of a lowboy or RGN trailer that connects the trailer deck to the fifth wheel of the tractor. On a fixed gooseneck trailer, this section is permanent. On an RGN trailer, the gooseneck detaches, allowing equipment to be loaded by driving forward over the lowered ramps. See also: RGN (Removable Gooseneck).

GVW / GVWR

Gross Vehicle Weight (GVW) is the total weight of the vehicle combination — tractor, trailer, and load — as measured at any point during the move. Gross Vehicle Weight Rating (GVWR) is the manufacturer-specified maximum design weight for a vehicle. The federal legal GVW limit on the Interstate System is 80,000 pounds; loads above this require an overweight permit. State limits on non-Interstate roads may be lower. GVW is distinct from axle weight — a load may be within the GVW permit limit but still require careful axle distribution to avoid exceeding per-axle legal limits at each bridge.

H

Heavy Haul

The transport of loads that exceed the standard legal weight or dimension limits for public highway travel. In practice, any load requiring an oversize or overweight permit is a heavy haul load. The term is also used more broadly to refer to the specialized segment of the trucking industry that handles permitted loads, as opposed to general freight carriers. R&RM LLC is exclusively a heavy haul carrier — permitted, oversize, and overweight loads are the entirety of our work.

Height Pole

A telescoping fiberglass staff mounted on the roof of a pilot car, set to the exact height of the oversize load. The height pole contacts any overhead obstruction — a low bridge, a utility line, a traffic signal — before the loaded truck reaches it, giving the driver advance warning. Height poles are required on lead pilot cars in most states for loads above 14 feet tall. See also: pilot car requirements by state.

High-Wide Load

An informal term for a load that is both taller than standard legal limits and wider than standard legal limits, requiring oversize permits for both height and width dimensions simultaneously. High-wide loads are among the most complex to permit because both dimensions trigger escort requirements and travel restrictions, and the combination of height and width may restrict the load to specific routes that satisfy both constraints.

Holiday Restrictions

Oversize load permit conditions that prohibit movement during federal or state holidays — and in some states, during specific holiday weekend periods (Friday before through Monday after Memorial Day, Labor Day, and Thanksgiving, for example). Holiday restrictions are standard in most states and must be accounted for when planning delivery windows. A load that needs to arrive by a specific date may need to depart earlier if a holiday weekend falls during the transit window.

Hours of Service (HOS)

FMCSA regulations governing the number of hours a commercial driver may operate in a given period. HOS rules apply to heavy haul drivers just as they apply to all commercial motor vehicle operators. The most relevant limits for multi-day heavy haul moves are the 11-hour driving limit per shift and the 70-hour/8-day or 60-hour/7-day on-duty limits. Permit travel windows (daylight only, no weekends) frequently determine driving schedules independently of HOS, but both constraints must be satisfied simultaneously.

L

Legal Dimensions

The standard highway limits within which a load can move without an oversize permit. Federal legal dimensions on the Interstate System: 8 ft 6 in wide, 13 ft 6 in tall (in most states), 53 ft trailer length, 65 ft total combination length (on most Interstates), 80,000 lb GVW. States set their own legal limits on state and local roads, which may differ from the federal Interstate standards. A load within legal dimensions does not require an oversize permit, though it may still require an overweight permit if it exceeds the GVW limit.

Lowboy Trailer

A trailer with a very low deck height — typically 18 to 24 inches off the ground — achieved by using a drop-down deck section between the gooseneck and the rear axles. The low deck allows tall equipment to be loaded without the total height (deck height + load height) exceeding the permit threshold. A standard lowboy is distinguished from an RGN in that the gooseneck is fixed rather than removable — equipment is loaded from the rear using ramps or a crane. Multi-axle lowboys add axle groups to distribute very heavy loads.

M

Multi-Axle Trailer

A trailer with more than the standard number of axle groups, used to distribute a heavy load's weight across enough axles that no individual axle exceeds legal per-axle weight limits. Standard trailer configurations have one to three axle groups. Heavy haul trailers may have 4, 6, 8, 10, or more axle groups for very heavy loads. The number of axles required is determined by dividing the load weight across the axle groups and verifying that each axle group satisfies both the per-axle limit and the bridge formula at every bridge crossing on the route.

O

Oversize Load

A load that exceeds one or more of the standard legal dimension limits (width, height, or length) but may or may not be overweight. An oversize load requires an oversize permit from each state it passes through and typically requires escort vehicles and specific signage. See our guide on how to get oversize permits.

Overweight Load

A load whose gross vehicle weight exceeds the legal GVW limit — typically 80,000 pounds on Interstate highways — or whose axle weights exceed legal per-axle limits, even if the load is within legal dimensions. An overweight load requires an overweight permit from each state it transits. Some loads are overweight but not oversize; others are both. Overweight permits specify the exact axle weights and gross weight authorized for the permitted route.

P

Permit Conditions

The specific restrictions and requirements attached to an oversize or overweight permit — including approved routes, travel time windows (daylight only, no Sundays, no holidays), escort requirements, speed limits, and any bridge or construction zone restrictions. Permit conditions vary by state and by load. The permit document issued by each state DOT is the authoritative source of what the carrier must comply with in that state; conditions supersede general state DOT rules wherever the permit specifies stricter requirements.

Pilot Car

A vehicle that travels ahead of or behind an oversize load to warn oncoming traffic, help navigate turns and clearances, and in some cases operate a height pole. Also called an escort vehicle or flag car. Most states require at least one pilot car when a load exceeds 14 feet wide or a specific height threshold. Loads over 16 feet wide typically require both a lead (front) and a rear pilot car. Pilot car operators in many states must hold a specific escort vehicle certification. See our guide on pilot car requirements by state.

Platform Trailer / Hydraulic Platform Trailer (HPT)

A trailer with a very low deck and multiple steerable axle lines, used for very heavy or dimensionally extreme loads that cannot be moved on standard lowboy or RGN equipment. Hydraulic platform trailers — also called SPMTs (Self-Propelled Modular Transporters) in their self-propelled form — use hydraulic suspension to keep the deck level over uneven terrain and can be assembled in modular configurations to carry loads of hundreds of thousands or even millions of pounds. See our guide on superload permits.

R

RGN (Removable Gooseneck)

A trailer type in which the front gooseneck section detaches from the trailer deck, allowing the front of the deck to lower to ground level. Equipment can then be driven forward directly onto the deck without needing a crane or forklift at the loading site. The gooseneck reattaches after loading. RGN trailers are the most common configuration for heavy construction equipment — excavators, dozers, loaders, compactors — because they allow drive-on/drive-off loading at most job sites. See our guide on RGN vs flatbed trailers.

Route Survey

A physical inspection of a proposed transport route by a qualified escort vehicle operator or engineer, conducted before the move to identify potential clearance problems — low bridges, tight curves, soft shoulders, utility lines — that may not appear on permit records or map data. Route surveys are required for superloads in most states and are recommended for any load above 14 feet tall or 16 feet wide traveling through unfamiliar corridors.

S

Single-Trip Permit

A permit that authorizes one specific oversize or overweight move, from origin to destination, within a specified time window. Single-trip permits are the most common permit type for heavy haul loads and are what most shippers encounter when moving a piece of equipment. Contrast with Annual Permit, which covers multiple moves within defined dimension limits throughout the year.

SPMT (Self-Propelled Modular Transporter)

A multi-axle platform vehicle with computer-controlled hydraulic suspension and independent steering on each axle line, used to move extremely heavy or large loads that cannot be transported on conventional trailers. SPMTs are used for loads like large industrial modules, transformers, bridge girders, and offshore platform sections. Multiple SPMT units can be linked together to carry a single load.

Step Deck Trailer

A trailer with two deck levels: a higher front section (above the wheel wells) and a lower main deck section aft of the wheel wells. The lower deck section is typically around 36 inches off the ground — lower than a standard flatbed but higher than a lowboy. Step deck trailers are used for loads too tall for a standard flatbed but not heavy enough or tall enough to require a lowboy. Common for loaded equipment that is 6 to 8 feet tall in transport configuration.

Superload

A load that exceeds the standard oversize permit thresholds — typically defined as a load over a certain weight (commonly 150,000 to 250,000 pounds GVW, depending on the state) or dimension (commonly over 14 or 16 feet wide or over 15 to 16 feet tall) that triggers a more stringent permit process. Superload permits typically require engineering analysis, longer lead times, law enforcement escorts, and coordination with utility companies for overhead line clearances. See our guide on superload permits.

T

Tandem Axle

Two axles grouped closely together (typically with axle spacing of 40 to 96 inches), treated as a unit for weight limit purposes. The federal legal limit for a tandem axle group is 34,000 pounds. Trailers commonly use multiple tandem axle groups to distribute load weight. Tridem axle groups (three closely spaced axles) are used on some heavy haul trailers for additional weight distribution.

Tie-Down

A chain, strap, or wire rope used to secure a load to the trailer deck. FMCSA Part 393 specifies minimum working load limit (WLL) requirements for tie-downs based on the weight of the article being secured, and sets rules for the number and placement of tie-downs for different load types and weights. Heavy equipment — excavators, cranes, large generators — typically requires chain tie-downs rated at a minimum WLL sufficient to resist the load's weight in all directions of potential movement.

Transport Weight

The actual weight of the equipment in its road transport configuration, which may differ significantly from the machine's operating weight. For cranes, transport weight is typically the carrier weight with the boom disassembled and counterweights removed or reduced to the minimum practical amount. For excavators, transport weight excludes any attachments (buckets, thumbs) removed for shipping and may reflect a reduced fuel and hydraulic fluid level. Carriers need the transport weight — not the operating weight — to select the correct trailer and determine permit requirements.

Trip Permit

See Single-Trip Permit.

U

Utility Clearance

The process of coordinating with electrical utilities, telephone companies, and cable operators to temporarily raise or de-energize overhead lines that a tall oversize load cannot safely pass beneath. Utility clearance is required on any route where overhead infrastructure is at or below the load's travel height plus a safety margin. On superload moves with loads above 18 to 20 feet tall, utility clearances can be the longest lead-time item in the permit process — utility companies may need 30 to 60 days' notice to schedule a clearance crew. See also: superload permits.

W

Wide Load

Informal term for a load that exceeds the standard legal width limit — 8 feet 6 inches in most states. An oversize width permit is required. Some states accept "WIDE LOAD" on the banner sign; others specifically require "OVERSIZE LOAD." See our guide on oversize load signage requirements.

Working Load Limit (WLL)

The maximum load that a tie-down (chain, strap, or wire rope) is rated to carry in service, as determined by the manufacturer and verified by testing. FMCSA Part 393 requires that the aggregate WLL of all tie-downs securing a load be sufficient to resist a forward force equal to the load's weight, a rearward force equal to 50% of the load's weight, and side and vertical forces equal to 20% each. For heavy equipment, this typically means multiple high-grade chains are required on each side of the machine.

Need Help With Your Heavy Haul Move?

Understanding the terminology is one thing — navigating the actual permit process, selecting the right trailer, and coordinating escorts across multiple states is another. R&RM LLC has been handling the full process for shippers since 2011. We serve all 48 continental states with oversize load transport, overweight load transport, and complete permit coordination.

Call us at (404) 987-6225 or submit a quote request with your load dimensions, weight, and route, and we'll handle the rest.