Flatbed, step deck, RGN, lowboy, stretch RGN, and multi-axle configurations explained — with specs, deck heights, weight limits, and real-world use cases. Know what you're requesting before you call a broker.
| Trailer Type | Deck Height | Deck Length | Max Payload* | Best For |
|---|---|---|---|---|
| Flatbed | ~60 in (5 ft) | 48–53 ft | ~48,000 lbs | Steel, lumber, machinery under 8'6" tall |
| Step Deck | Lower deck ~48 in | 48–53 ft | ~46,000 lbs | Loads 8'6"–10' tall that can crane-load |
| RGN | ~24–30 in | 48–53 ft std | ~42,000–65,000 lbs | Drive-on equipment: excavators, cranes, rigs |
| Lowboy (Double Drop) | ~18–22 in | 24–53 ft well | ~40,000–80,000 lbs | Very tall, heavy equipment — max height clearance |
| Stretch RGN | ~24–30 in | 48–130+ ft | ~42,000–80,000 lbs | Wind blades, long beams, crane booms |
| Multi-Axle Heavy Haul | ~18–24 in | Custom | 200,000–500,000+ lbs | Transformers, pressure vessels, reactor vessels |
* Payload capacity varies by axle count, state permit rules, and configuration. Legal gross vehicle weight without permits is 80,000 lbs. Figures shown are approximate maximums under standard permit conditions.
The flatbed is the workhorse of heavy freight. It's exactly what it sounds like: a flat, open deck with no sides, no roof, and no height restriction above the deck. That openness makes it the fastest to load and unload — freight can be craned, forklift-loaded, or slid on from any side. The tradeoff is legal height: with the deck sitting around 60 inches off the ground, you only have about 8'6" of clearance before you hit the standard 13'6" bridge height limit.
Flatbeds are legal anywhere in the US without permits as long as your load stays within standard dimensions: no wider than 8'6", no taller than 13'6" at the highest point of load, no longer than 53 feet overall, and no heavier than 48,000 lbs of cargo (80,000 lbs gross). Once you exceed any of those limits, you're in oversize territory and need a different trailer, permits, or both.
A step deck has two deck levels separated by a single vertical step. The front (upper) deck is short — typically 10 to 11 feet — and sits at standard flatbed height. Behind the step, the main lower deck drops roughly 8 to 12 inches, running the remaining 37 to 43 feet to the rear. That drop buys you critical height clearance: loads on the lower deck can be approximately 10 inches taller while still clearing standard bridge heights.
Step decks are the natural next step up from flatbeds when your equipment is too tall for a standard flatbed but can still be crane-loaded or forklift-loaded — and doesn't need the extreme low deck of an RGN or lowboy. Think large agricultural machinery, tall industrial equipment, construction equipment that isn't self-propelled, or anything in the 8'6" to 10' height range.
The RGN is the go-to trailer for large construction equipment. RGN stands for Removable Gooseneck — the front section that connects to the tractor's fifth wheel can be hydraulically detached from the main trailer frame. When the gooseneck is removed, the front of the trailer lowers to the ground, creating a drive-on ramp. Equipment with wheels or tracks — excavators, bulldozers, cranes, drill rigs, mining equipment — can power directly onto the deck under their own steam, no crane required.
With the gooseneck attached, the deck sits at about 24 to 30 inches off the ground — significantly lower than a step deck and low enough to move equipment that would be impractical on any higher platform. The lower deck height means more clearance above the load before hitting bridge height limits. RGNs typically run with three to five rear axles on standard configurations, with additional axles added for heavier loads.
Hydraulic vs. mechanical RGN: A hydraulic RGN (HRGN) uses hydraulic cylinders to raise and lower the gooseneck, making attachment and detachment fast — often 15 to 30 minutes. A mechanical RGN uses a manual pin-and-bracket system that's slower but results in a lighter trailer weight, which means more usable payload.
The lowboy — also called a double drop — is the lowest legal trailer deck available in standard configurations. The name "double drop" describes the trailer's distinctive shape: the deck drops once right behind the gooseneck connection, runs at an extremely low height (typically 18 to 22 inches from the ground) through the main cargo area, then rises again before the rear axle bogie. That ultra-low well is the defining feature — it gives you the most height above the deck of any trailer, typically allowing loads up to 11'6" to 12' tall under standard bridge clearances.
Unlike an RGN, a standard lowboy has a fixed gooseneck — it doesn't detach. Equipment is loaded either from the rear using built-in ramps or by crane. This makes tare weight lighter than an RGN, which translates to more payload capacity at the same gross vehicle weight.
Lowboys are the right call when you're moving the heaviest, tallest equipment: large cranes (minus boom), industrial presses, construction equipment at maximum height, large generators, and oversize power transformers. When weight exceeds standard lowboy capacity, additional axles are added to the rear bogie — which is where 13-axle configurations begin.
A stretch RGN is a standard RGN with a hydraulically or mechanically extendable midsection. When retracted, it behaves like a standard RGN. When extended, the deck can reach 80, 100, even 130 feet or more — long enough to move loads that would be physically impossible on any fixed-length trailer.
The most common application in the US is wind turbine blades, which can exceed 200 feet in length. Stretch RGNs used for wind blades incorporate an articulating "blade runner" or "saddle" at the rear that allows the blade to rotate and flex around curves. Outside of wind energy, stretch RGNs handle long structural steel sections, bridge girders, prestressed concrete beams, and telescoping crane boom sections.
Any stretch RGN move will require special long-load permits in every state and typically requires at least two pilot cars (one at front, one at rear). Moves may be restricted to certain times of day and specific routes. Routing must be pre-surveyed for tight turns, low bridges, and overhead utilities.
When a load exceeds what any standard trailer can handle — typically 150,000 to 200,000 lbs and above — you enter superload territory. The solution is to add axles. A lot of them. Each axle distributes the load's weight across more road contact points, keeping the per-axle force within state-legal limits and protecting road surfaces from damage.
A "13-axle" configuration includes 3 tractor axles plus 10 trailer axles, with steering capability at both front and rear of the trailer. These are not off-the-shelf trailers — they're purpose-built or modular systems (Goldhofer, Scheuerle, Nicolas, Kamag, Mammoet, Sarens) that can be linked side-by-side and end-to-end to match the exact footprint needed for the cargo. Loads moved on multi-axle platforms include power transformers, nuclear reactor vessels, pressure vessels, oil refinery columns, and large ship components.
Superload permits are a different category entirely. Every state reviews them individually, route surveys are required, and turnaround times of 2 to 6 weeks are common. Some states require engineering studies of bridges along the route. Police escorts are mandatory. Moves are restricted by weather, time of day, and day of week. Perpetual coordinates the full permit package and logistics across all state lines.
Give us the make, model, dimensions, and weight of your equipment. We'll tell you exactly what trailer it needs, what permits are required, and what it'll cost — same day.