(a) In general Subchapter II of chapter 1015 of title 54, United States Code, is amended by adding at the end the following: 101513. State law (a) Definitions In this section: (1) Off-highway vehicle The term off-highway vehicle shall be defined by the State in which the applicable System unit is located, in accordance with the law of the State. (2) Road The term road means the main-traveled surface of a roadway open to motor vehicles that is owned, controlled, or otherwise administered by the Service. (b) Applicable law The law of the State in which a System unit is located shall apply to the use of motor vehicles (including off-highway vehicles) on roads within a System unit. (c) Violations Violating a provision of State law applicable to a System unit under subsection (b) shall be prohibited in the applicable System unit.. (b) Clerical amendment The analysis for subchapter II of chapter 1015 of title 54, United States Code, is amended by adding at the end the following: 101513. State law..