Why Trailer Type Matters in Heavy Haul
In standard freight, the choice between a dry van and a flatbed is straightforward — it comes down to whether the load is packaged and weather-sensitive, or not. In heavy haul, trailer selection is a technical decision that affects permit requirements, route options, loading complexity, and overall cost. The wrong trailer can mean the load is too tall to clear bridge restrictions, too heavy per axle to use the permitted route, or impossible to load at the origin site.
R&RM LLC has moved oversize and overweight loads since 2011, operating RGN trailers and coordinating multi-axle configurations across all 48 continental states. When we receive a quote request, trailer selection is one of the first determinations we make — before permits are applied for, before escorts are scheduled, before the move is priced. This guide explains how that decision is made and what each trailer type is built for.
Get a Quote for Your LoadRemovable Gooseneck (RGN) Trailers
How RGN Trailers Work
A removable gooseneck trailer — universally called an RGN in the industry — is defined by its detachable front section. The gooseneck connects the trailer deck to the fifth wheel of the truck and supports the forward load weight. When it is disconnected and pulled forward, the front of the trailer deck lowers to the ground, creating a ramp. Equipment that moves under its own power — tracked excavators, wheeled dozers, graders, and similar machinery — drives directly onto the trailer from the front.
When the equipment is in position, the gooseneck is backed under the front of the trailer and reconnected. The deck rises to its transport height, typically 18 to 24 inches off the ground, and the load is secured. This process is faster than crane loading and does not require a crane to be on-site at the origin — a meaningful advantage on active jobsites where crane availability cannot be assumed.
Best Uses for RGN Trailers
RGN trailers are the workhorse of construction and mining equipment hauling. Excavators, bulldozers, motor graders, scrapers, wheel loaders, and similar self-propelled heavy equipment are almost always transported on RGN trailers when their dimensions and weight allow. The low deck height — typically 18 inches — means most equipment stays within legal height limits even with an attachment folded or removed, which simplifies permit requirements significantly.
RGN trailers are also used for non-self-propelled equipment that requires a low loading angle: long industrial modules, structural steel assemblies, and fabricated equipment that cannot tolerate the steep angle of a rear-only ramp. For these loads, the front-ramp loading of an RGN is often the only practical option.
RGN Weight and Dimension Limits
A standard 3-axle RGN trailer can carry approximately 40,000 to 42,000 pounds of payload. Adding booster axles or rear jeep dollies extends capacity — a 4-axle configuration can carry around 55,000 pounds, and 5-axle and 7-axle configurations push capacity to 70,000 pounds and above. The legal limit is determined not just by trailer capacity but by the bridge formula applied to the axle configuration on the specific permitted route.
Standard RGN trailers are available in lengths of 24 to 53 feet of effective deck space. Extended RGN trailers with additional neck length or stretch configurations accommodate equipment that extends beyond the standard deck. Most RGN trailers have a deck width of 8 feet 6 inches between stake pockets — wide enough for most construction equipment, though some larger equipment requires a wider deck or overwidth permits regardless of trailer width.
Lowboy Trailers
Standard Lowboy Design
A standard lowboy trailer has a fixed neck — the connection point between the trailer and the truck does not detach. The load is placed on the trailer by loading from the rear using a pair of ramps that fold down from the tail of the trailer, or by crane. The fixed neck design is structurally simpler and generally less expensive to own and operate than an RGN, but it limits loading options to rear-ramp or overhead crane methods.
Lowboy decks sit between 18 and 24 inches from the ground depending on the manufacturer and axle configuration. This is comparable to an RGN, which means height clearance calculations are similar between the two trailer types for loads of the same dimensions. The key practical difference is loading: a lowboy requires either a significant approach grade for rear-ramp loading or a crane at the pickup site.
Multi-Axle Lowboy Trailers
Multi-axle lowboys add rear axle groups beyond the standard 2-axle rear configuration to distribute load weight across more axles, which reduces individual axle loads and allows the trailer to carry heavier payloads in compliance with bridge formula limits. A 3+2 configuration (three front axles plus two rear axles) can carry substantially more weight than a 2+2 configuration, and 4+4 or more configurations are used for very heavy loads.
The additional axles also improve stability and steering control on heavy loads — a critical factor when a fully loaded trailer is approaching 300,000 to 400,000 pounds gross. Multi-axle lowboys are typically used for cranes, large mining equipment, and heavy industrial modules that exceed the capacity of a standard 3-axle RGN even with full booster axle additions.
Step Deck (Drop Deck) Trailers
A step deck trailer — also called a drop deck — has two deck levels: a shorter upper deck near the truck, and a longer lower deck that drops down behind the rear axle of the truck. The upper deck is typically at standard flatbed height (about 4 feet from the ground), and the lower deck drops to approximately 3 feet from the ground.
Step decks are used for loads that are too tall for a standard flatbed but do not require the very low deck height of an RGN or lowboy. Equipment in the 10 to 11 foot tall range often fits on a step deck under legal height limits (13 feet 6 inches standard) when it would be too tall on a flatbed. Typical step deck loads include agricultural equipment, industrial machinery, construction prefab sections, and vehicles that cannot travel under their own power.
In heavy haul, step decks see limited use for the heaviest loads because their structural capacity is lower than lowboys or RGNs, and their deck height is not low enough for the tallest equipment categories. They occupy a useful middle ground between standard flatbed and heavy lowboy for loads that are awkward in height but moderate in weight.
Standard Flatbed Trailers in Heavy Haul
Standard flatbeds — deck height of approximately 4 to 5 feet, no drop sections — are used in heavy haul for loads that are overweight or overlength but not particularly tall. Wide or long structural steel, large fabricated components, and equipment that sits low to the ground relative to its weight can sometimes be moved on a flatbed when the height allows.
When a load is overweight but its height on a flatbed would exceed legal limits (13 feet 6 inches in most states), the carrier must use a lower-deck trailer option. For loads that are wide but not heavy enough to require a multi-axle configuration, a standard flatbed may still be acceptable. Flatbeds are the most common trailer in general freight, which means availability is high and per-mile cost is typically lower than specialized heavy haul trailers — when a flatbed works, it is usually the most cost-effective option.
Hydraulic Platform Trailers (Modular Trailers)
What Hydraulic Platform Trailers Are
Hydraulic platform trailers — sometimes called modular trailers, Goldhofer trailers (after the dominant manufacturer), or self-propelled modular transporters (SPMT) — represent the highest tier of heavy haul equipment. These trailers consist of multiple modular axle units linked together, with hydraulic suspension that allows the deck height to be raised and lowered independently at each axle group. They can be configured in virtually unlimited axle arrangements and widths by connecting modules in series or parallel.
The hydraulic system serves two critical functions. First, it allows the deck height to be adjusted so that the load platform remains level even on grades, protecting sensitive equipment from tilt. Second, it distributes weight with precision across every axle — critical for loads where the bridge formula must be satisfied across a very large footprint to stay within permit limits on each individual axle.
When Hydraulic Platform Trailers Are Required
Hydraulic platform trailers are typically deployed for loads that exceed 150,000 to 200,000 pounds, are extremely wide (over 20 feet), or are so large and rigid that no conventional trailer can accommodate them. Common loads include large power transformers, chemical reactors, offshore platform modules, nuclear components, and very large mining equipment in the 400-ton class.
These trailers are expensive to operate, require specialized drivers trained on hydraulic systems and multi-axle synchronization, and must often be transported to the job site from a significant distance. Lead time for hydraulic platform moves is measured in weeks, not days, and route surveys conducted well in advance of the move are standard practice. Moves of this type represent a small fraction of heavy haul volume but the highest-stakes and most technically complex segment of the industry.
How to Know Which Trailer Your Load Needs
Height-Driven Trailer Selection
The most important dimension for trailer selection is the height of the load. A standard flatbed deck sits about 5 feet off the ground. Add 13 feet 6 inches of legal maximum height and the equipment can be no taller than approximately 8 feet 6 inches on a flatbed. An RGN or lowboy deck sits at 18 to 24 inches, which means equipment up to about 11 feet 6 inches to 12 feet tall can clear the standard height limit — enough for most excavators with booms lowered and most dozers without a blade raised.
Equipment taller than 12 feet in transport configuration will require an overheight permit regardless of trailer type. The carrier calculates the exact transport height and applies for the appropriate permit. Very tall loads — transformers that stand 16 feet or more — require route surveys to identify low bridges, utility crossings, and overhead obstructions that must be cleared or scheduled around.
Weight-Driven Trailer Selection
Once height is addressed, weight drives axle configuration. Federal bridge formula limits under 23 U.S.C. § 127 restrict the maximum weight that can be applied to any axle group based on the span between axle groups. A heavy load must spread its weight across enough axles — and those axles must be spaced far enough apart — to comply with the formula on the permitted route.
The carrier's permit team calculates the required axle configuration when preparing the permit package. If the load's weight requires more axles than the trailer has, booster axles (jeep dollies) are added to the front of the combination, or the trailer is upgraded to a multi-axle configuration. When weight requirements exceed what conventional trailers can handle, hydraulic platform equipment is brought in. Our permit services team manages this calculation as part of every heavy haul move we coordinate.
Width-Driven Trailer Considerations
Width affects permits but typically does not change the trailer type the way height and weight do. Most RGN and lowboy trailers have a standard 8-foot-6-inch deck width, which matches the standard legal highway width. When equipment is wider than the trailer deck — a wide excavator, a crane with counterweight attached, or an industrial module — the load overhangs the trailer sides and the full width of the equipment is what triggers the overwidth permit threshold.
Very wide loads may require a different trailer configuration to manage the overhang safely, particularly for loads that are much wider than they are long. In some cases, a wider deck is available and reduces the overhang, which can simplify escort requirements if the narrower overhang keeps the total width under a threshold that would otherwise trigger additional pilot cars.
Trailer Selection in Practice
Most construction equipment moves — excavators, dozers, loaders, scrapers, and cranes up to 100 tons — fit comfortably on a 3-axle or 4-axle RGN with straightforward permit packages. The drives-on characteristic of the RGN makes loading fast and does not require crane availability at the origin site, which is a practical advantage on busy job sites.
Larger equipment — 100-ton-class mining excavators, crawler cranes in transport configuration, large paving trains — typically requires multi-axle lowboy or RGN configurations. At this scale, crane loading at the origin is common because the equipment is too heavy for its drive systems to power up loading ramps under full configuration. Disassembly of booms, counterweights, or other components may be required to bring the load within permit parameters, which adds time to the loading process and re-assembly time at the destination.
For the heaviest and widest loads, hydraulic platform trailers are the only viable option. R&RM LLC coordinates these moves through our network of specialized equipment partners and handles the full permit package for any trailer configuration. Call (404) 987-6225 or use our quote form to discuss your load's requirements — we will confirm which trailer type it needs as part of the quoting process.
Frequently Asked Questions
What is the difference between an RGN and a lowboy trailer?
The defining difference is how the gooseneck connects the trailer to the truck. An RGN's gooseneck detaches, lowering the front of the trailer to the ground so that equipment can drive on from the front. A standard lowboy has a fixed neck — the trailer must be loaded from the rear via ramp or by crane from above. Both sit at similar deck heights, but the RGN's drive-on capability is faster and more practical for most self-propelled construction and mining equipment.
How much weight can an RGN trailer carry?
A 3-axle RGN carries approximately 40,000 to 42,000 pounds of payload within federal bridge formula compliance. Adding booster axles increases capacity — a 4-axle configuration carries around 55,000 pounds, and 5-axle configurations reach 70,000 pounds or more. Maximum payload on any specific move depends on the permitted route's axle weight limits and the bridge formula calculation across the full truck-trailer combination.
When is a hydraulic platform trailer required?
Hydraulic platform trailers are deployed for loads exceeding conventional multi-axle trailer capacity — typically 150,000 to 200,000 pounds and above — or for loads that are so wide or dimensionally unusual that no fixed-deck trailer can accommodate them. Power transformers, large chemical vessels, industrial modules, and ultra-class mining equipment are the most common categories. These moves require weeks of planning and are significantly more complex and expensive than standard heavy haul.
What trailer is used for excavators?
Most excavators from 20 tons to 100 tons are transported on 3-axle or 4-axle RGN trailers. The RGN's drive-on capability is ideal for tracked excavators, which drive under their own power onto the lowered deck through the detached gooseneck. Very large excavators in the 100-ton class and above may require multi-axle configurations or hydraulic platform equipment depending on their transport weight and height. See our excavator hauling page for more on common configurations.