Numbers

A MAJOR accident in the Channel Tunnel resulting in 70 or more deaths will happen once in 100,000 years, according to a report by Eurotunnel. Impressive, but how was it calculated?

Give or take a few millennia, 100,000 years is the time homo sapiens has been around; 10,000 years ago, you could walk from England to France without getting your feet wet. So how did Eurotunnel look 100,000 years into the future? It began with the statistics from 1984-90, which showed a total of 313 people killed in railway accidents in Britain, including 99 at stations. With 268 billion passenger kilometres travelled, simple arithmetic yields figures of 0.08 fatalities per 100 million passenger kilometres, plus 0.95 fatalities per 100 million passenger journeys (for those killed at stations). These figures, and their French equivalents, were then combined and applied to the tunnel, as though it were a randomly selected 50km stretch of track with a station at each end.

The figure may then be modified by the decreased likelihood of anyone throwing himself in front of a moving train under the Channel. Fires and derailments, however, (estimated at 4.4 per cent and 18.5 per cent respectively of the 'total system risk') are likely to have more serious consequences, which are, in turn, balanced by more stringent safety procedures.

Eurotunnel concludes: 'The Channel Tunnel represents a significant advance in railway safety', which may be true. But for all the precision, it is little more than informed guesswork: 100,000 years is a long time on a train line. The Titanic was unsinkable. Has Eurotunnel overlooked an iceberg, too?