 The road passes along the hillsides by the northern outskirts of central Naples; passing through 3.6 km of tunnels through the steep hills and across 3.3 km of impressive viaducts passing high above older structures.The road is one of the most congested motorways in Italy, with over 270,000 vehicles using it every day, traffic levels possibly rivaling those of the A4 through Milan and the A8 near the Milan barrier toll plaza.On 9 February 2009 the "Tutor" speed monitoring system became operational on the Tangenziale di Napoli, encouraging motorists to abide by the 80km/h speed limit.