questionText: 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 Chiltern Tunnel; and which other transport or infrastructure projects have subsequently adopted, or are expected to benefit from, those lessons and methods.
answerText: 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...
heading: High Speed 2 Line: Tunnels