There is a statute known as the Amtrak Act (Amtrak Reauthorization and Improvement Act of 1990, Public Law 101-322) that provides that if a motor carrier employee provides regularly assigned duties in two or more states he shall only be taxed in the state of residence. The act specifically refers to "residence" not "Tax Home."
A copy is at uscode.house.gov/statutes/pl/101/322.pdf
