Double Drop & Lowboy Trailer: Dimensions, Permits & What It Hauls
A double drop or lowboy is the trailer you need when freight is too tall or too heavy for a flatbed or step deck. These loads sit in a well that's just 18–24 inches off the ground, which means tall freight can clear overpasses that nothing else can handle. They come with more complexity — permits, pilot cars, route surveys — so knowing what triggers each requirement is part of the broker's job.
What Is a Double Drop Trailer?
A double drop trailer (also called a lowboy) has three sections: a high front gooseneck that attaches to the tractor, a low well section where the freight rides, and a rear deck that rises back up for the tail end. The well is the lowest point of the trailer — typically 18–24 inches from the ground — which allows the tallest legal loads to clear bridge clearances that flatbed and step deck equipment cannot handle.
The term "lowboy" is commonly used interchangeably with "double drop" in everyday brokerage. Technically, a removable gooseneck (RGN) is a specific type of lowboy where the front ramp detaches, allowing tracked equipment to drive onto the trailer from the front. A fixed-neck double drop must be loaded from the rear or with a crane.
Double Drop Trailer Dimensions
Typical double drop / lowboy specifications
| Spec | Measurement |
|---|---|
| Well length (freight area) | 20–29 ft (varies by trailer) |
| Total trailer length | 48–53 ft common; longer with stretch |
| Well height from ground | 18–24 in (~1.5–2 ft) |
| Max freight height (no permit) | Up to 11'6" in most states |
| Deck width | 8'6" standard; wider with permits |
| Std payload (fixed neck) | 40,000–45,000 lbs |
| Heavy haul payload (RGN) | 60,000–80,000+ lbs with additional axles |
Height Math on a Lowboy
With a well height of 18 inches from the ground and a federal legal clearance of 13'6" (162 inches), freight in the well can be up to 11'0"–11'6" tall before permits are required — about 2'6" more than a step deck. That extra clearance is why lowboys exist.
| Well Height | Max Freight Height | Total Height |
|---|---|---|
| 18 in | 11'6" | 13'0" |
| 20 in | 11'4" | 13'0" |
| 24 in | 11'0" | 13'0" |
Permit Thresholds
Oversize and overweight permits are issued per state. A load crossing five states needs five permits. The thresholds that trigger a permit are based on any of the following dimensions exceeding legal limits:
| Dimension | Federal Legal Limit | Permit Triggered When |
|---|---|---|
| Height | 13'6" | Over 13'6" |
| Width | 8'6" | Over 8'6" |
| Length | 53' | Varies by state — typically over 53' |
| Weight | 80,000 lbs GVW | Over 80,000 lbs |
Most lowboy freight is permitted for height or weight. A standard permit (single-trip, daytime only) costs $15–$75 per state. Permits can take 1–5 business days to process in most states. Some states (like California) take longer.
Pilot Car and Escort Requirements
Most oversize loads on a lowboy require a pilot car (also called an escort vehicle). Requirements vary by state, but the general thresholds are:
- Over 12' wide: front pilot car required in most states
- Over 14'6" wide: rear escort also required in most states
- Some states require police escorts for loads over 16' wide
- Night travel restrictions apply to most oversize loads — daytime movement only in many states
- Some states restrict oversize movement on Sundays or holidays
RGN vs Fixed-Neck Lowboy
| Feature | Fixed-Neck Lowboy | RGN (Removable Gooseneck) |
|---|---|---|
| Loading method | Crane or rear ramp | Drive-on from front or crane |
| Best for | Crated equipment, tanks, steel | Tracked equipment (excavators, dozers) |
| Availability | More common | Less common, higher cost |
| Setup time | Faster | Longer — gooseneck removal takes 30–60 min |
Broker Checklist Before Quoting a Lowboy Load
- Get all four dimensions: length, width, height, and weight
- Ask how the equipment is loaded — does it drive on (needs RGN) or does it require a crane?
- Identify all states on the route — each needs a separate permit, call the carrier's permit department
- Build permit lead time into the pickup date — 2–5 business days minimum, longer in CA and some others
- Ask whether a pilot car is included in the carrier's quote or separate
- Confirm the carrier runs superloads (over 80k lbs) if the weight is significant
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