Autopistas are specifically reserved for automobile travel, so all vehicles not able to sustain at least are banned from them. Thus, they may not be an upgrade to an older road, since the Spanish legislation requires an alternate route to be provided for such vehicles. Many, but not all, autopistas are toll roads, which also mandates an alternate toll-free route (though not necessarily a freeway) under the Spanish laws. An example is the AP-2 toll autopista, which links Zaragoza with Barcelona through the Monegros desert. In this case, the alternative is the N-II, the national road that preceded the A-2 autovía.