It is illegal under state law to operate on public highways a combination of a tractor and two trailers with a combined length of the trailers of more than 61 feet without a special permit.

Operators of overlength vehicles must obtain a special permit from the Washington State Department of Transportation (WSDOT) to travel on the state highway system. Permits issued may be valid anywhere from one day to one year.  WSDOT is authorized to issue a one-year permit for operation of two trailing units which together are no more than 68 feet in length.  WSDOT must charge a $100 fee for the permit.

WSDOT is authorized to issue a one-year special permit for operation of two trailing units hauling fluid or liquid nondivisible milk, which together are not more than 85 feet in length.  WSDOT must charge a $300 fee for the permit.