Las Raíces Tunnel, Road tunnel in Chile

Las Raíces Tunnel is a 4,528 m road tunnel on Route 181 through the Cordillera de Las Raíces, linking Curacautín and Lonquimay at 1,010 m above sea level. Its portal is built of dark grey stone blocks, framed by a band of lighter, roughly cut voussoirs and a horizontal lighter stone band beneath a flat parapet. The bore is 4.2 m wide and 5.6 m high, and from its midpoint neither entrance is visible.

Feasibility studies began in 1911 and final blueprints were ready in 1929; construction ran from 1930 to 1940 at a cost of over 32 million pesos of the time. It was driven by a proposed bioceanic railway linking Talcahuano and Bahía Blanca that was never completed, so the tunnel instead served the Púa–Lonquimay branch line from 1956 until the 1990s, when it passed to road traffic. During the works a landslide sealed the entrance and trapped 42 workers inside for more than ninety hours.

Traffic runs one way only, controlled by signals at each portal, so vehicles wait until the direction is indicated before entering. A toll station charges per car and higher rates for trucks over two axles; oversized trucks use the gravel Cuesta de Las Raíces branch instead. Average volume is about 450 vehicles a day, including fuel trucks from Argentina.