Chilterns Tunnel

The Chiltern Tunnel is a high-speed railway tunnel in Buckinghamshire and Hertfordshire, England, which will carry the High Speed 2 (HS2) railway line under the Chiltern Hills. The twin-bore tunnels, which are 16.04 km (9.97 miles) long, are the longest on the HS2 line. Each tunnel also has additional 220 m (720 ft) entry and 135 m (443 ft) exit perforated concrete portals to reduce sudden changes in air pressure and subsequent noise. A contract for the tunnel's construction was awarded in 2017; preparatory work commenced during the following year. In May 2021, it was announced that excavation had commenced. The boring process, which was largely performed by a pair of tunnel boring machines (TBMs), advanced at an average speed of 15 m (49 ft) per day; both TBMs completed their drives by March 2024. Civil engineering work on the tunnel was completed by January 2026.

Tunnel data from Wikidata (CC0). Summary from Wikipedia (CC BY-SA).