Question to the Department for Transport:

To ask His Majesty's Government what is the standard design speed on the main route of HS2 Phase 1; and what speed restrictions planned in each tunnel are due to their reduced diameter and the piston effect of the train.

The HS2 route alignment has been designed to enable operation at speeds up to 360km/h on main route north of the northern portal of the Chiltern Tunnel where the topography and other constraints permit a suitable track alignment to be constructed. Between Euston and the Chiltern Tunnel north portal, the design speed progressively increases to a maximum of 320km/h.

There are no speed restrictions planned as a result of tunnel diameter or the piston effect of the train.