High Speed 2 Line: Tunnels
2026-06-21 · Department for Transport · 11820 · Official question
Question
To ask the Secretary of State for Transport, with reference to the HS2 six-monthly report to Parliament published in May 2026, what lessons learned and innovative construction methods were deployed in the completion of the north portal structure at the Ch
Answer
The Chiltern Tunnel North and South Portals have been specially engineered with perforated concrete hoods to prevent the possibility of sudden changes in air pressure and a resulting ‘sonic boom’ caused by trains entering and exiting the 10-mile-long tunn...