Washington's normal legal semi-trailer length is 53 feet. A Single Trailer Permit allows a semi-trailer and/or its load to extend to 56 feet, measured from the front of the trailer or load to the rear of the trailer or load, whichever is longer.
The permit can be used for divisible or non-divisible loads within the applicable permit limits.
Example
If your tractor-trailer has:
- A 53-foot trailer → generally no Single Trailer Permit is needed based solely on length.
- A 54-foot trailer/load → a Single Trailer Permit may be required.
- A 55-foot trailer/load → a Single Trailer Permit may be required.
- A 56-foot trailer/load → a Single Trailer Permit can cover the additional length.
- More than 56 feet → the standard Single Trailer Permit does not cover the combination; another permitting situation may apply.
WSDOT's permit guide states that an overlength permit is required when a tractor/semitrailer exceeds 53 feet, while a divisible load may be permitted up to 56 feet with the Single Trailer Permit.
How Is the 56-Foot Length Measured?
The measurement is important because Washington does not simply measure the trailer itself.
For a single trailer, WSDOT measures from the front of the trailer or load to the rear of the trailer or load, whichever produces the greater distance, up to the permitted 56 feet.
This means the dimensions of the cargo can affect whether a permit is necessary.
Single Trailer Permit Fees
WSDOT currently lists:
| Permit | Cost |
|---|---|
| 30-day Single Trailer Permit | $100 |
| Annual Single Trailer Permit | $1000 |
The permit is available through WSDOT's permit program.
What Restrictions Does the Permit Waive?
One useful feature of the Washington Single Trailer Permit is that it is exempt from several restrictions, including:
- Commuter-hour restrictions
- Holiday restrictions
- Oversize-sign requirements
- Nighttime travel restrictions
- Certain winter restrictions
However, carriers still have to comply with applicable chain requirements and other safety restrictions.
Single Trailer Permit vs. Oversize/Overweight Permit
These permits should not be confused.
A Single Trailer Permit is specifically available for the longer single-trailer configuration up to 56 feet. A separate WSDOT oversize/overweight permit is used for qualifying non-divisible loads that exceed legal dimensions and/or weight.
For example, if a truck is carrying a non-divisible load that is both overweight and overlength, the carrier may need an oversize/overweight permit rather than relying solely on the standard Single Trailer Permit.
What About a 53-Foot Trailer?
A standard 53-foot semi-trailer is within Washington's legal trailer length, so a Single Trailer Permit is generally unnecessary when the combination otherwise complies with Washington's size and weight requirements. WSDOT identifies 53 feet as the legal tractor/trailer length.
Single Trailer vs. Double Trailer Permit
The two permits cover different configurations:
| Permit | Maximum permitted length | Typical configuration |
|---|---|---|
| Single Trailer | 56 ft. | Tractor + one trailer |
| Double Trailer | 68 ft. | Tractor + two trailers |
WSDOT lists both as $100 for 30 days or $1000 annually.
A double-trailer permit is not interchangeable with a single-trailer permit.
Important: Check the Route
Having a permit does not eliminate the carrier's responsibility to check the route. WSDOT states that carriers must verify route restrictions and overhead clearances before moving permitted loads.
Also, WSDOT permits apply to state routes. Separate authorization may be necessary when traveling on certain city streets or county roads.
Bottom Line
A Washington Single Trailer Permit is primarily needed when a single-trailer combination exceeds the normal 53-foot legal length but remains within the permit's 56-foot limit. The current WSDOT fee is $100 for 30 days or $1000 annually.