Letter: Switched on to electric buses

Sir: In the interesting correspondence about non-polluting road transport in cities (Letters, 4 July), there was no mention of fly-wheel storage, which could be important if trolleybuses were to be resuscitated.

For a vehicle to proceed without being connected to an energy supply, such as a powerline, it needs stored energy. The most efficient energy storage is by petrol or diesel oil - a full fuel tank provides several hundred kilometres of travel. Batteries are less efficient - they need recharging after about 50 kilometres. Storage by high-speed flywheel, which would provide electric power while the vehicle is not connected to a powerline, is an attractive alternative. It is true that the storage density weight for weight of a flywheel is only about one-tenth that of an accumulator, but it has the advantage that it can be recharged in a few minutes while batteries need several hours.

I suggest an integrated electrical transport system by trolleybuses be considered. In outlying areas the bus would draw power from overhead lines while simultaneously recharging its flywheel. In areas from which, for aesthetic or other reasons, overhead lines are excluded, the bus could travel for five to six kilometres on its stored energy. The flywheel would be recharged when the bus rejoined an overhead line or at strategically located stops with charging facilities.

Yours faithfully,

N. KURTI

Department of Engineering Science

University of Oxford

Oxford

5 July