Question to the Department for Transport:

To ask the Secretary of State for Transport, whether a further review of the tunnel boring machine advance rates for the High Speed 2 Chiltern tunnel has yet taken place.

HS2 Ltd have carried out an extensive reviews of tunnel boring rates for comparable forms of tunnel (looking at the size of tunnel and type of tunnel boring machine used) as part of the work for the hybrid Bill development, including tunnels both in this country and overseas. Particular attention has been made to ascertaining the ‘hard average rate’ achieved on these tunnels, which is much more appropriate in calculating the overall time to complete a particular tunnel drive for its entire length from "machine in to machine out". HS2 Ltd have provided evidence from these applicable tunnel projects in front of the Select Committee and explained on several occasions how the tunnel drive rates from these other projects support the current assumed drive rate for the HS2 Chiltern Tunnel. No further review is considered to be required as there is no further appropriate evidence available.