Question to the Department for Transport:

To ask Her Majesty’s Government what is the (1) internal diameter, (2) cross-sectional area, and (3) maximum design speed allowable, in each of the HS2 train running tunnels, and what assessment they have made of how those compare to equivalent running tunnels on high speed lines in France.

The design of HS2 tunnels has been considered in three separate groups, namely:

1. Cut & Cover tunnels,
2. Bored Tunnels with a maximum nominal line speed up to and including 230km/h,
3. Bored Tunnels with a maximum nominal line speed of between 231 km/h and 360km/h.

a, Cut & cover tunnels are twin cell tunnels with each cell measuring 7m wide x 9m high, giving a cross sectional area of 63m² for a maximum nominal line speed of 360km/h.

b, Bored tunnels with a maximum nominal line speed up to and including 230km/h have been designed with an internal diameter of 7.55m, giving a cross sectional area of 44.77m².

c, Bored tunnels with a maximum nominal line speed between 231 km/h and 360km/h have been designed with an internal diameter of 8.8m, giving a cross sectional area of 60.82m².

The cross sectional area of a tunnel is dependent is on a number of factors, including; maximum nominal line speed, tunnel length, railways structure gauge, railway system spatial requirements, aerodynamics including statutory requirements, operations and maintenance requirements including evacuation and safety. The impact of these factors has been assessed when determining the appropriate diameter/cross sectional area of each of the tunnels on the HS2 Phase 1 route. For this reason it is not appropriate to make a direct comparison between HS2 tunnels and those constructed in France or elsewhere in the world.