It connects the Cantabrian Atlantic Coast at Santander to Palencia.

It forms part of the Autovía A-8 until Torrelavega where it heads south through the Cantabrian mountains along the Besaya River.

The road then passes south west to Aguilar de Campoo.

Because it crosses the Cantabrian mountain range from north to south, this communication route has routes of great technical complexity, including five viaducts, including the Montabliz viaduct, which became the highest bridge in Spain on its opening day and the sixth in Europe, being the most expensive work on the entire highway.

The viaduct crosses the Bisueña river bed 145 meters above the ground.