This is the huge 10-mile HS2 tunnel being built that will take 200mph trains just three minutes to pass through. Sonic booms can be caused by high-speed trains forcing air forwards when they enter a tunnel - but this has been designed with special measures in place to prevent it. The huge structure heads under the Chiltern Hills and took almost three years to bore through the land. It's on the route to Birmingham - and in June 2024, HS2 Ltd assessed the cost for the line to be up to £66 billion.

Inside HS2's longest tunnel

Inside the longest HS2 tunnel | The Mirror