Drinking hot coffee on a bus is normally a bad idea, but passengers will be encouraged to try it on a new service that promises to be as smooth as the most modern train.

No one will need to “hold on tight”, as Routemaster conductors used to cry. Indeed, the driver will be instructed to take his hands off the wheel and allow the bus to steer itself.

The only difference between the St Ives to Cambridge buses and their standard counterparts is two small guide wheels attached in front of the regular wheels. These engage with a concrete channel that is being built along 16 miles of disused railway line across the Fens.

When the service begins in late summer it will be by far the world's longest guided busway, more than twice as long as the current longest in Adelaide. Its impact will be felt far beyond the severely congested A14 commuter corridor in Cambridgeshire. The Department for Transport (DfT) is determined to prove that guided buses are much cheaper and more flexible than trains or trams. Several other disused railway lines are earmarked for conversion to busways and, in the longer term, some branch lines could be concreted over and carry rubber tyres instead of steel wheels.

Unlike trains, buses can pick passengers up in scattered villages before joining the busway for an uninterrupted 60mph glide across the countryside. In the city, they switch back to roads. The DfT also believes that busways will be far cheaper to maintain than railways. The Cambridgeshire busway is designed to operate without any significant maintenance for 40 years. A railway needs weekly inspections, regular repairs to damaged points and rails, as well as an expensive signalling system.

If a busway has to be closed, the buses would simply avoid that section by switching to roads. Cambridgeshire County Council, which is building the busway, estimates that the maximum delay from such a diversion would be five minutes, compared with an hour or more if a railway line closes.

The council believes that the busway will be safer than rail because the braking distance of buses is a tenth of that of trains. Buses also accelerate more quickly than trains, so they can stop more frequently to pick up passengers without adding to journey times unduly. The busway will carry a bus every eight minutes; comparable branch lines carry one train an hour.

The £116million cost of the busway is being funded by the taxpayer, but the operating costs, including the buses themselves, will be paid by the bus companies. They will also pay a small access fee to cover the cost of busway maintenance. Branch lines require large annual subsidies for train services and maintenance.

Bob Menzies, the head of the busway project, said: “We think [people] will be attracted by the smoothness of the ride, leather seats and free wi-fi. We want people to be able to ride on the busway having a cup of coffee with their laptop open, catching up on e-mails.”

St Ives to Cambridge city centre takes 50 minutes in the peak period by car but will take 32 minutes by bus.

Disused railways being considered for busways include routes from Luton to Dunstable, Bath to Bristol and some old track beds near Portsmouth.

Bruce Williamson, of Railfuture, which campaigns for rail expansion, said: “The DfT has gone for a cheap and nasty option after riding roughshod over local opinion in favour of reopening the train line. Trains are greener than buses because steel wheels on steel rails have much less rolling resistance, and therefore use less energy, than rubber on concrete.”

Matt Bradney, the council's cabinet member for transport, claimed that busways would win enthusiasts as passionate as those who support the railways — but he admitted “it might take another 150 years”.

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