This Act enhances penalties for drivers who cause serious physical injury, as defined in § 222 of Title 11, to a vulnerable user, as defined in this Act. For a person to be guilty under this Act, the injured vulnerable user must be lawfully using a highway, defined in § 101 of Title 29 as "the entire width between boundary lines of every way or place of whatever nature open to the use of the public as a matter of right for purposes of vehicular travel . . . ."