BRITAIN’S Health & Safety Executive took the drastic step on April 29 of serving on Railtrack a Prohibition Notice limiting trains in the 7 km tunnel under the Severn estuary to 32 km/h. First Great Western’s inter-city services between London and South Wales were disrupted, along with those of other operators. As the Severn tunnel is worked as one 8 km block section, only four trains an hour could pass through in each direction. Emergency track renewal work at night and weekends should have seen the speed limit restored to 120 km/h on May 24.

HSE said it had issued the notice because four broken rails had been found inside the double-track bore within seven months, ’20 times greater than the national average for the type of rail used in the tunnel.’ It attributed the breaks to corrosion caused by the huge inflow of water to this undersea tunnel. Because of this water, track circuits were replaced by axle-counters in 1987, thus eliminating the mechanism that automatically detects most broken rails before they cause a derailment.

Unfortunately, this is not an isolated incident. Recent months have seen an alarming increase in rail breaks, especially on the West Coast main line between London and Rugby - the most heavily used section of Britain’s busiest inter-city route. Between October 1 and February 28, there were 53 breaks south of Rugby compared to 12 a year earlier even though last winter was mild. Railtrack hurriedly ordered the installation of an extra 32 km of rail.

On the day the Severn tunnel notice came into force, passengers on the 05.19 Virgin inter-city train from Wolverhampton to London had a hair’s breadth escape from disaster at Hemel Hempstead on the WCML. While passing over a recently renewed switched-diamond at 175 km/h, rail in the crossing shattered into seven separate pieces. Mercifully, the locomotive (which probably did the damage) was propelling from the rear, and somehow the whole train managed to stay on the rails.

In its March 1998 Network Management Statement, Railtrack forecast 600 broken rails during the year to March 31 1999, down from 756 in 1997-98. As it turned out, there were about 900, a forecasting error of 50% over 12 months. This does not suggest that rail defects are under control, and the underlying reason is fairly clear.

Two years ago, Railtrack was still expecting to replace only 0·8% of rail in its 32000track-km network in each of the next 10 years. That forecast rested on assumptions about the total gross tonnage that its rail would and should carry rather than current experience in Europe, where +2% annual renewal rates are the norm. Although Railtrack has actually been renewing 80% more rail than its official target, the rate looks certain to climb higher in response to these latest incidents.