the national network was most "recently" defined by the intermodal surface transportation efficiency act of 1991. information on these routes are taken from §658 appendix a. some states such as indiana, arkansas, and ohio allow truck traffic on all "numbered" state or u.s. highways. other states, such as new york and california, have a specially defined set of highways which are recommended for trucks. the law allows for "reasonable access" to and from the nn for terminals, deliverires, trucks stops, repairs, and other reasons. the nn is recommended for "through" truck traffic (e.g. traffic that is passing through the area), and trucks are allowed to operate on truck-restricted roads if they have no other means of access to their destination.