16 Dec 2010
Replacing the HST fleet
But the underlying problem has not gone away. There are many routes in Britain that are electrified for only part of their length. The alternatives are either to run diesel-powered trains on electrified lines or to change the motive power where the electrification comes to an end.
Locomotive changes are awkward and undesirable as they involve shunting in congested locations. There is, however, a long-established technique that gets rid of most of the inconvenience. It was employed on the line between London and Weymouth, which was electrified as far as Bournemouth. The four cars at the London end of the trains comprised a 3000 hp unit (4-REP, photograph above) capable of powering a 12-car train. The eight cars at the country end of the trains comprised two 4-car trailer control units (4-TC) each with a driving cab at both ends. In the Weymouth direction, the trains were driven from the leading cab in the trailer unit, with the REP power unit pushing the train. At Bournemouth, the REP was detached and the front TC units hauled to Weymouth with a diesel locomotive. In the other direction, the diesel locomotive pushed the train back to Bournemouth, where it coupled to a REP unit which hauled it to Waterloo. In this way, locomotive movements at the changeover point were minimised.
A similar situation will develop on the Great Western main lines, where electrification is likely to extend only as far as Oxford, Newbury, Bristol and Cardiff. A similar solution suggests itself, with the electric power being provided either by locomotives or with special high powered EMU sets. The trailer sets will need to have vehicles with driving cabs, probably in two varieties: one with a streamlined front for 125 mph speeds, and another with a blunter end and gangway connection. The latter type would be placed at the London end of trains from, say, Cornwall, from where they would be pushed to, say, Bristol and then couple to the electrically powered portion of the train. The streamlined driving cars would be at the country end of trains, which would split and be hauled over non-electrified tracks to their destination.
London to Bristol could of course be operated by conventional EMU trains similar to the class 444 used on the longer distance services out of Waterloo. Given the number of stops on the GW main line, there is little benefit in 125 mph operation and little opportunity these days for sustained fast running, a further build of class 444 units or their successors would be adequate. And it would not be disastrous if services between London and Devon/Cornwall were diesel powered all the way, with under-the-wires running between London and Newbury.
Whatever the case, the operator will need a uniform and flexible fleet of passenger vehicles which can be deployed in alternative configurations to suit the line and its traffic conditions. It may be that the best solution would be a standard fleet of hauled stock made up into fixed formations with between five and seven vehicles, with diesel and electric locomotives as traction.