Every open-deck trailer is answering the same two questions: how tall can the freight be before the load is over-height, and how does the freight get onto the deck. Once you know your load’s height, width, weight and how it moves, the choice of trailer mostly makes itself.
The height arithmetic
In the United States there is no single federal height limit for trucks. Each state sets its own, and most land between 13 ft 6 in and 14 ft. California allows 14 ft; much of the eastern half of the country holds to 13 ft 6 in. In Canada each province sets its own limit too — Ontario’s is 4.15 m, about 13 ft 7 in.
Whatever the limit, the arithmetic is the same:
Legal freight height = the height limit − the height of the deck the freight sits on.
So the lower the deck, the taller the freight can be without an over-height permit. Typical figures, at a 13 ft 6 in limit:
| Trailer | Deck height (typical) | Freight height (about) |
|---|---|---|
| Flatbed | about 5 ft | 8 ft 6 in |
| Step deck — main deck | about 3 ft 4 in – 3 ft 6 in | 10 ft |
| Low-pro step deck — main deck | about 3 ft – 3 ft 2 in | 10 ft 4 in |
| Double drop or RGN — well | about 1 ft 6 in – 2 ft | 11 ft 6 in – 12 ft |
These are industry-typical numbers. Every trailer is a little different, so a real quote always checks your load against the actual trailer.
Width and weight
Width is simpler: 8 ft 6 in (102 in) is the legal width on the main US highway network, whatever the trailer. Anything wider is oversize and needs a permit from every state — and every Canadian province — on the route.
Weight works against the low trailers. The usual gross limit on US interstates is 80,000 lb for the truck, trailer and freight together, so a heavier trailer leaves less room for payload. Typical legal payloads:
- Step deck: roughly 45,000–48,000 lb
- RGN lowboy (standard configuration): roughly 40,000–42,000 lb
Above that, a load is overweight: it needs permits, and often a trailer with more axles to spread the weight.
How the freight gets on
This is where the trailers really split.
A step deck is lifted onto. Its deck is open on both sides and on top, so a forklift can load it from the side, a crane from above, or a loading dock from the back. Self-propelled equipment can go on with ramps or a dock, but it is not the step deck’s strength.
An RGN is driven onto. RGN means removable gooseneck: the neck that connects the trailer to the truck detaches, the front of the deck lowers to the ground, and it becomes a ramp. An excavator, dozer or loader drives straight on under its own power. No crane, no dock.
A fixed-neck double drop has the same low well as an RGN but its neck does not come off, so it is loaded from the side by crane or forklift. Most RGNs are double drops; not every double drop is an RGN.
Which one, then?
A rule of thumb that gets most loads right:
- Lifted on, under about 10 ft tall — machinery on skids, crated equipment, steel, pipe, lumber, building materials: step deck.
- Drives on under its own power — excavators, dozers, wheel loaders, backhoes: RGN.
- Taller than about 10 ft but under about 12: RGN or double drop, to stay at legal height.
- Wider than 8 ft 6 in, or overweight: an oversize permit, on whichever trailer suits the rest of the load — usually the RGN.
- Farm tractors and implements: it depends on the model, the height and how it loads. Send us the make and model.
Ask before you book
The difference between a legal load and an oversize one can be two inches — an exhaust stack, a cab guard, a mirror. Measure to the highest, widest and longest points, with attachments, in the position the machine will travel in. If you are not sure how, our guide to measuring a load for a quote walks through it.
Then send the numbers. We run a 53 ft low-pro step deck and an RGN lowboy, and we will tell you straight which one your load needs — or if it needs something we do not run.