 It is a single carriageway highway for most of its route.Strada statale 4 "Via Salaria" starts Northeast of Rome, just outside the Aurelian Walls, where until 1921 Porta Salaria was located to control access to the city.The initial stretch of SS 4 is more similar to an urban road than to a highway, as the area has now become densely populated and buildings have been raised by the roadside.