Sardinia is the only Italian region without Autostrade (en:motorways), but the road network is well developed with a system of no-toll roads with dual carriageway, called "superstrade" (en: super roads), that connect the principal towns and the main airports and seaports; the speed limit is /. The principal road is the SS131 "Carlo Felice", linking the south with the north of the island, crossing the most historic regions of Porto Torres and Cagliari; it is part of European route E25. The SS 131 d.c.n links Oristano with Olbia, crossing the hinterland Nuoro region. Other roads designed for high-capacity traffic link Sassari with Alghero, Sassari with Tempio Pausania, Sassari – Olbia, Cagliari – Tortolì, Cagliari – Iglesias, Nuoro – Lanusei. A work in progress is converting the main routes to highway standards, with the elimination of all intersections. The secondary inland and mountain roads are generally narrow with many hairpin turns, so the speed limits are very low.