HS2 has now completed mining half of the Chiltern Tunnel emergency cross-passages. 

HS2 Ltd said it has now finished mining 19 out of 38 underground emergency cross-passages linking the northbound and southbound tunnels.

Unlike the main tunnels carrying the high-speed trains, the shorter emergency passages are being excavated by two

These shorter emergency passages are being dug by remotely controlled mini-excavators unlike the main tunnels carrying the high-speed trains, which are excavated by two giant tunnelling machines Florence and Cecilia.

HS2 Ltd’s project manager Aaron Harrison said: “We’re making great progress on the Chiltern tunnel with approaching 9 out of 10 miles complete, and our cross-passage teams are catching up fast. Once complete, HS2 will dramatically improve journeys between London and the West Midlands, unlock tens of thousands of new homes and free up space on the busiest part of the West Coast Main Line.

 “While invisible to the travelling public, these hidden passages have a key role in providing a safe operational railway so it’s great to see such good progress.”

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Chilterns Tunnel is the high-speed railway’s longest tunnel stretching 10 miles through Buckinghamshire countryside.

When complete, the tunnel will see trains whiz through at speeds of up to 200mph between London and Birmingham.  

Construction of the passages 


Once the emergency passages are complete, they will be temporarily sealed for fire safety reasons before permanent safety doors will be installed at either end.

The sliding doors have gone through a rigorous fire and fatigue testing to factor in high train speeds, associated pressures and frequency of the trains.

In an emergency, passengers can use the emergency walkways in each tunnel to safely evacuate the train and walk through the cross passages into the other tunnel where they can be rescued on a passenger train.

Access for the emergency services is from either the portal or one of the five ventilation shafts.

Construction is currently underway for five additional short tunnels known as ‘adits’ that connect the shafts to the running tunnels, with the mining of two of the ‘adits’ already complete.

Tunnel boring machines Florence and Cecilia are expected to break through at the north portal early next year.