It’s a bus… on tracks
This is the story of a railway that closed because of bus competition - only to re-emerge as a 'railway' carrying buses. We have seen derelict railways converted to footpaths; now, in Cambridgeshire, we are seeing a development which closely resembles the precursor to the railways - the guided trackway. Or in this case, the conversion of a derelict railway into a guided busway.

The advice of the Government's CHUMMS
The passenger service on the line between Cambridge and St Ives survived until 5th October 1970. A freight service was retained as far as Histon but this ceased in 1983. Freight to Fen Drayton survived until 1992 because of a long-term aggregates contract.

Following the complete closure of the line, most of the track remained in-situ apart from the last few miles to St Ives. In 1994, Cambridgeshire County Council put forward a proposal to purchase the land and the surviving track in order to restore a passenger service. This never happened. In the late 1990s, the Government launched the Cambridge to Huntingdon Multi-Modal Study (CHUMMS), chiefly to address the chronic local traffic congestion. The study suggested a guided busway along the Cambridge-St Ives route. This would involve replacing the track with a concrete busway and the demolition of the stations to provide guided busway stops. Buses would travel along the disused line, continuing through Cambridge on normal roads and join the guided busway at Cambridge Railway Station to travel through to Addenbrooke's Hospital and the Trumpington Park & Ride.

Longest busway anywhere in the world
The scheme went before a public inquiry in 2004. Cambridgeshire County Council awarded a 'Design and Build' contract to BAM Nuttall Ltd in the summer of 2006. The detailed design of the guided busway has been undertaken in a joint venture between Arup and Parsons Brinkerhoff Ltd. Eventually, construction started in 2007 with the remaining track being lifted.
So far, all of this is generally available non-technical knowledge. But how does a guided busway work in practice. What is it made of and how is it constructed?

Arup has been working on the project from an early stage and has developed ideas from the few existing busway projects around the world. In the UK there are short sections in Leeds (11/4 miles), Crawley (250yds) and Ipswich (200yds).

In Germany, Essen has a four mile busway whilst in Adelaide, Australia, a 71/2 mile scheme is in operation.

The Cambridge to St Ives project is by far the longest anywhere in the world at 16 miles.

Extremely tight tolerances
Essentially, the busway is a concrete ladder made up of a pair of precast concrete beams linked by precast concrete spacers. All of the components are precast locally in a factory production process. The contractor has 28 moulds and the capacity to produce 14 ladder beams per day. The beams have a 700mm wide bus running surface and a 180mm high guideway upstand.

They and the spacers are cast to extremely tight tolerances in steel moulds. The ladder panels are 15m long and landed on foundations every 71/2m. These foundations are either spread footings or piled foundations, depending on the ground conditions. When assembled, the space between the beams is filled with shredded tyre rubber, top soiled and then seeded. All that should be visible once the system has matured will be the concrete running surface and the upstands of the beams.

In all but the tightest of curves, the individual beams units are straight. This has not proved to be a problem at the proposed line speed of 60mph. Neither is there any superelevation. If horizontal curvature has to be catered for, this is done at the casting stage by precision packing out the upstand section of the steel moulds.

No signalling
The buses - all standard vehicles - are fitted with jockey guide wheels which are attached to the steering track rod ends. It is a very simple and basic system. The jockey wheel is 90mm diameter. For the high speed running sections, there is just +3mm tolerance in the 2,600mm gauge between guide faces. For slow speed running, this can be relaxed to +5mm.

The guide wheel gauge is set at 2,605mm to ensure that there is always contact between the wheels and the upstands. Essentially a permanent engineering structure, there are facilities to adjust top and line by jacks should this be necessary to maintain the ride quality in the future.

At level crossings, the upstands are flared away from the track at exit and entrance points. There are traffic light controls which always give priority to the buses. The 'six foot' is narrow - the desirable dimension being 800mm. It can go down to 700mm in places.

All the system so far is double track and there is no need for signalling. Buses drive on line of sight.

Design handbook
Kulvinder Rayat of Arup has been working on the scheme right from the start. He was involved in the trial running on the first section to be built. "We started running buses at about 20mph and gradually increased the test running speed to a maximum of 60mph. It was extremely smooth with the joints between the sections barely detectable.'

Guided busways now have their own design handbook. Developed by Arup for Britpave, it deals with all the aspects of busway planning, design and construction.

The busway is due to open later this summer. With it will come a direct link between the new housing in St Ives, the proposed eco town in Oakington and the renowned technical park to the north of Cambridge, with connections through to the railway station and hospitals. The precision of the engineering should make this project a far cry from the distant days of wagon wheels running in stone grooves. And what did that evolve into?!

Article courtesy of The Rail Engineer- may 2009


Further Info
Peter Bishop - Head of Public Relations & Corporate Communication
BAM Nuttall Limited
St James House, Knoll Road, Camberley,
Surrey GU15 3XW
Tel: 01276 63484
Fax:01276 66060
peter.bishop@bamnuttall.co.uk