Semi-trucks pulling double or triple trailers are legal on the USDOT designated national highway network based on load weight restrictions. The laws of the NHTSA also establish some provisions each state must follow in regard to these trucks on secondary state highways; the rules essentially keep states from prohibiting truck and trailer rigs on secondary roads so long as they are within certain length and weight parameters. Drivers towing trailers must meet all the qualifications required by the FMCSA which include, but are not limited to being: 21 years or older, English-language capable, trained and licensed and not disqualified due to criminal behavior while hauling or unsatisfactory safety or accident record.
In 2009, "Automobile Magazine" published a map of states that do and do not allow double trailer towing; when published, the only states that did not allow double towing were: Washington, Oregon, Maine, Vermont, New Hampshire, Massachusetts, Rhode Island, New York, Connecticut, West Virginia, Virginia, North Carolina, South Carolina, Georgia, Florida, Alabama and Hawaii. If you plan to tow a travel trailer with a boat behind it, for example, check the laws for each state you will travel through before you go; they may disallow double trailer travel entirely, or may allow it with restrictions on overall length of combined tow vehicle and trailers. The NHTSA also advises you to thoroughly familiarize yourself with the towing capacity first of the tow vehicle, with an eye to the combined load of both trailers, then to the capacity of the first trailer to maintain a following trailer safely. Although special permits may be required, you do not need a special driver's license to tow double trailers.
From time-to-time the FMCSA works with states to develop a new or temporary highway system in the network; this might occur in order to facilitate bringing over-sized equipment into a mining or drilling facility. Most of the time, however, state's rules apply. If you drive semis or personal vehicles, you may be able to obtain special permits through each state's department of transportation (DOT) to tow double trailers, or over-sized double trailers if you can demonstrate the need for such permits. For commercial drivers, it may be easier to use a multi-state private permitting service; but both tractor-trailer drivers and private individuals should be able to obtain necessary permits from the individual states' DOTs.
