Hobby Horses

De inertia urbanorum

BMJ 1994; 309 doi: https://doi.org/10.1136/bmj.309.6970.1741 (Published 24 December 1994) Cite this as: BMJ 1994;309:1741
  1. Ronald Williams, general practitionera
  1. aLondon SW1X 9SW

    When I first started using a bicycle for my home visits in central London 22 years ago I had in mind only fine sunny days. But I saved even more time when it was wet, for the cars then clogged the streets in even greater numbers. Now, 87000 cycling km (54000 miles) later, the disparity between the slowness of the motor car and the swiftness of the bicycle is so apparent that some comparison of these vehicles—and their effects—is called for.

    In the first century BC Cicero knew the difference between inertia and velocitas. But he can hardly have imagined, or been equipped to analyse, the complexities of the machines and mechanisms now in question, even though the remarkably quiet and highly developed power unit of the modern bicycle is identical in all important respects to that used by the ancient Romans in getting themselves on foot to the forum.

    Furthermore, the efficiency of the car engine in converting chemical energy into mechanical work is only 20%1 whereas that of the cyclist is about 25%.2 This is hardly surprising, for our fuelling, motor, and control systems have been refined and tested, often to destruction, under appallingly rigorous conditions over 500 million years. Fortunately, we can still use this clean and extremely complex equipment to advantage even in 20th century London, although not while we remain strapped in our cars. It is a source of continuing wonder to me that healthy general practitioners will sit inert behind their steering wheels, queuing for half an hour to cross a bridge, when they could reach their destination in a fraction of the time on a bicycle. It is not as if all that much effort were required, for the cyclist uses five times less oxygen and energy—than the walker in covering …

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