Research and analysis

Proposal for an extension north of the HS2 Northolt tunnel

A detailed engineering review of an alternative proposal for an extension of the HS2 Northolt tunnel under the Colne Valley


Proposal for northern extension of Northolt tunnel SIFT report


The HS2 Phase One Environmental Statement includes a proposal for a viaduct across the Colne Valley. However, those affected by this proposed viaduct have requested that a tunnel should be provided under the Colne Valley in lieu of a viaduct.

A more detailed assessment was undertaken to compare having a tunnel as opposed to a viaduct across the Colne Valley. This report by HS2 Ltd provides a detailed review of a tunnel option at Colne Valley versus a viaduct. The tunnel option has been developed in enough detail so that the tunnel and viaduct options can be compared against each other with consideration of the engineering requirements, rail systems impacts, practicality, costs, programme implications and environmental impacts.

Published 9 March 2015