High Speed Rail Bill Select Committee: Statement by the Chair

We heard extensive argument on the case for a Colne Valley Tunnel from Hillingdon Borough Council and from local residents and residents groups. Notably, we heard from the council's engineering expert about tunnel engineering and estimated costs.

The main arguments for a tunnel are to mitigate operational noise and community environmental impacts, and to eliminate the effects on Hillingdon Outdoor Activities Centre, a highly valued amenity. 

Subsidiary arguments included that a tunnel would affect the local hydrogeology less than pile-driven viaduct supports; another was that a tunnel would be less expensive to maintain than a surface route on a viaduct. Based on the evidence and cross-examination, those subsidiary arguments were not convincing.

Estimates of the net additional cost of a tunnel over a viaduct generally exceeded £200m, although there was disagreement on how to arrive at an appropriate assessment. We do not direct further studies because we doubt that these would converge on a figure significantly less than £200m.

Importantly the evidence was that a tunnel would not eliminate the impact of construction works in Hillingdon and surrounding areas. It would bring its own set of construction requirements.

Our main concern is about the impact of construction work in this area. As the tunnel option carries its own set of construction issues, our overall view is that a convincing case for a tunnel instead of the viaduct has not been made.

In our earlier statement this week, we requested a report on construction railhead options and potential haul road adjustments. When we have that, we will consider construction and traffic issues further. They need close scrutiny.

We need more reassurance on traffic modelling. In the meantime, we want a push, now, toward a satisfactory compromise for HOAC, including a possible staged move. The Committee would like to see HOAC carry on its activities in one place or another but recognises the difficulty of staying on at the current site.

The fact that the HS2 project will not be bearing the cost of a Colne Valley tunnel means that attention should now be directed toward significant further interventions in Hillingdon to mitigate the effect of the railway and its construction on the community—interventions that should be additional to those already envisaged. We are satisfied, for instance, that the restoration of right of way amenities after construction will be effective, but during construction there will be a heavy impact on footpath amenity and on local traffic. We hope that more can be done on this and other issues.

We agree that the viaduct should be of the best design. We heard suggestions of a design competition. We ask that option to be considered.