Bielsa Tunnel is an international high mountain tunnel at an elevation of 1.820m (5,971ft) above the sea level, located in the Pyrenees, on the border of Spain and France.
The tunnel is 3.07km (1,90 mile) long and opened in October 1976. Open to traffic throughout the year, may be closed for short periods in winter when the weather is bad. The road features some steep sections, up to 11.8%. The tunnel passes the Pyrenean chain between Aragnouet and Bielsa, and links the Hautes-Pyrénées department in southwestern France and the province of Huesca, Aragon, in northern Spain.
On the Spanish side, the road to the tunnel is called A138. It’s paved. Starting from Salinas, the ascent is 21 km long. Over this distance, the elevation gain is 1.028 meters. The average percentage is 4.9 %.
On the French side, the road to the tunnel is called D173. It’s asphalted but in worse conditions. Starting from Saint Lary Soulan, the ascent is 18.93 km long. Over this distance, the elevation gain is 1.000 meters. The average percentage is 5.3 %. The maximum slope is 11.8%.