Rush-hour deterrent - Telegraph Concrete balls the size of grapefruits could solve passenger overcrowding, according to a bright spark at Indonesian state railways. The balls will be suspended from gantries to deter those who prefer to ride on train roofs. While this may prove an exciting variation on the action film cliché of the train-roof struggle, it could make life on the 8.15 to Jakarta a little too interesting. "They don't have to sit on top," said an official, in the true tones of petty bureaucracy. If the train is full, we will be happy to reimburse them. But brave roof-class travellers are made of stern stuff. "We like it up there," said one. Whatever happens, South West Trains must not hear of this. No doubt a non-lethal deterrent to commuters packing carriages too tightly could be developed in their workshops. Watch out for signs declaring: "Waterloo twinned with Jakarta Gambir."