provided for such vehicles. Many, but not all, autopistas are toll roads, which also mandates an alternative 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. On the other hand, autovías are usually (though not always) upgrades from older roads, and always untolled. In general, slow vehicles like bicycles and agricultural machinery are allowed under certain restrictions so as to not disrupt the traffic excessively or cause any danger. Furthermore, an autovía will most likely follow the original road very closely, only deviating from it to bypass the towns (which are looped around in variantes). Thus, the upgraded road usually serves as the base for one of the two directions of the new autovía, which means the turns can be steeper than in autopistas. All in all, an autovía: Allows traffic banned from an autopista, like bicycles. However, if the autovía is built as a new road instead of an upgrade to an older one, this traffic may be banned too. May have little to no hard shoulders, which are then marked with a solid line instead of the broken line of a transitable hard shoulder. May have acceleration and deceleration lanes that are much shorter than those of autopistas. May have tighter turns and steeper gradients than an autopista is allowed to. If space-constrained, it may even have bus stops on a service lane in the autovía itself, as opposed to requiring them to be placed on a service lane physically separated from the main road. Also if extremely space-constrained, there can be acceleration and deceleration lanes merging on the left lane of the autovía. However, most of the situations listed here only apply to the oldest autovías, and mainly to the radial A-1 through A-6 plus the A-42 near their endpoints, which were the first to be twinned in the 60s into dual carriageways (with at-level intersections) and then were upgraded to limited-access freeways in the 70s-80s, keeping most of their old route unchanged except where the old national road ventured into towns. In those cases, the freeway would make a semi-loop called a variante around the town, leaving the old national road as the access between the freeway and the town. New autovías