World-class tunnelling expertise exists in Cambridge (e.g. Centre for Smart Infrastructure and Construction at Department of Engineering, Mott MacDonald, Atkins, Skanska, etc.). One of the world authorities on tunnelling is Professor Lord Robert Mair (CBE FREng FRS), who is Sir Kirby Laing Professor of Civil Engineering and Head of Civil and Environmental Engineering at the University of Cambridge. He has been involved in a wide range of rail tunnelling projects worldwide, including being closely involved with the design and construction of the Jubilee Line Extension for London Underground, the Channel Tunnel Rail Link, and Crossrail projects. According to Prof Lord Mair, the thick gault clay deposits that underlie Cambridge are eminently suitable for tunnelling.
Our latest 2021 scheme revised the scope of tunnelling. Originally, we proposed a tunnel link from the Central Rail Station to Cambridge North Station. However, this has been removed for several reasons: a) the heavy rail line already provides services between these two stations; b) our new overland route from the West Campus to the Science Park enables fast journeys without the need for a tunnel; c) a second tunnel was more complex to deliver; and d) the expense could not be justified given there were good alternatives in a) and b) above.
By eliminating one of the tunnels we have reduced the overall tunnel length to 2.6 km, and this is now a single, simple bi-directional tunnel extending from the Mill Road area to Grange Road. There would be two underground stations: one at the central city, which could be either at Market Square or at Drummer Street (or even under Grand Arcade); a second at Parkside. The latter stop would facilitate easy access for the lower Mill Road area, including Anglia Ruskin University, law courts and close to the commercial shops at the Grafton Centre. We recognise that underground stations are expensive (we have allowed £100 M per station in our cost estimates), and this is why only a limited number are likely to be possible. However, at Parkside it might be feasible to construct the station nearer to the surface using cut and cover methods, which could substantially reduce costs in this location.
The south portal would be close to Mill Road, near the rail bridge, and would occupy space currently used for station parking. We envisage a stop on the surface near the tunnel entrance, enabling access from the southern Mill Road area. The west portal would be in the vicinity of Grange Road, potentially near the Cambridge University Rugby Club. This location would help to minimise the length of tunnel necessary, as well as enable a surface stop near the portal to serve local facilities such as the Rugby Club, the University Library, West Road Concert Hall, Law and Arts Faculties, the Sidgwick site, as well as local residents. We anticipate this stop would increase in importance if the plans announced by the consortium of Colleges to create a new residential community on the West Fields gain momentum. A precise location for the portal and stop has yet to be identified, and is open for discussion.
By reducing the length and complexity of tunnelling, as well as the number of underground stations, we have massively reduced the cost of Cambridge Light Rail. The estimated cost of the tunnel is now ~£160 M based on a per km cost of £61 M, which is comparable to tunnelling projects elsewhere. An additional £200 M has been allocated for the two underground stations, bringing the total cost of the tunnel and stations to ~£400 M. While this is a substantial investment, this is for the long-term and the marginal extra cost over the alternative of surface running may not be as much as many would expect. Surface running in the city core will encounter many challenges such as city sewage, water and electrical services, historic buildings, archaeology, difficulties presented by existing infrastructure / properties etc, and solving these constraints will also incur significant costs. The tunnel, on the other hand, will avoid most of these constraints, and thereby avoid a lot of those costs.
Our tunnel proposal is modest compared to the scheme put forward for the Cambridgeshire Autonomous Metro (CAM). The CAM plans presented to date propose a tunnel of ~12 km in length and four portals, with the four tunnel ‘tails’ joining at two underground junctions, and only a single underground station at the centre. Based on the length alone, the cost of CAM tunnel would be a minimum of £732 M. Add to this £100 M for the underground station and several hundred million for the complexity of the undertaking, the tunnelling costs alone are likely to exceed £1 bn. Taking into account that CAM is based around some form of electric bus, which has yet to be revealed or proven as an operational metro, then the risks of this enterprise are daunting. In our view, this CAM tunnel scheme is very unlikely to be financed or deliverable because of its scale, cost, complexity and risk.
In contrast, Cambridge Light Rail has a measured, minimal, and simple tunnelling plan focused on essential needs at the lowest cost possible, while still delivering an exceptional solution for Cambridge. We believe this is far more pragmatic, realistic and deliverable. We hope political parties, local authorities, business, and residents will get behind it.
