23 U.S. Code § 127- Vehicle Weight Limitations- Interstate System
(S) Natural Gas and Electric Battery Vehicles- A vehicle, if operated by an engine fueled primarily by natural gas or powered primarily by means of electric battery power, may exceed the weight limit on the power unit by up to 2,000 pounds (up to a maximum gross vehicle weight of 82,000 pounds) under this section.
Consistent with the FAST ACT Maryland provides an allowance up to 2k for alternative fuel vehicles on the interstate system and Maryland State routes.