Sir – The unwelcome proposals to build on the Green Belt beyond Grenoble Road could significantly overload Oxford’s buses.

In 1948 Thomas Sharp assessed that Oxford’s bus and road networks could not expand to serve more than 100,000 residents.

His calculation included his proposals for new relief roads, half of which have never been built. Oxford has some good bus services, but parts of our city have limited road space in which to keep increasing them. A major enlargement of Oxford would need trams, to whose capital costs developers should substantially contribute.

Bus routes 1, 2, 5, 7 and 8 are already so busy and frequent that trams would make more sense. Trams do not need a population of 250,000 to justify them as Martin Smith claims (Letters, March 26). In Germany, Potsdam’s population is a similar size to Oxford’s and the populations of Darmstadt, Schwerin, Würzburg and Zwickau are significantly smaller. Each has a tram network between 12 and 25 miles long that it has recently rebuilt or extended.

Martin proposes trolleybuses. These would not reduce emissions as much as trams, because rubber tyres on asphalt are much less energy-efficient than steel tyres on steel rails. Only about five per cent of Britain’s electricity is carbon-free. Ninety-five per cent burns carbon and emits climate-damaging gases: either at power stations or by mining and extracting uranium. Trolleybuses need more overhead wires than trams. Except in “wire-less” city centre sections this would mean more visual clutter than necessary.

Ian East (Letters, April 2) is right: one articulated tram can replace several buses while using less road width. Würzburg’s trams serve narrow medieval streets where no bus could fit.

About 15 miles of tramway could link Kidlington, Barton and Blackbird Leys to central Oxford and the rail station. Oxford needs this, and the county should seriously propose it.

Hugh Jaeger, Oxford