Alternating current track circuits have certain advantages over direct current track circuits, particularly in respect to their immunity to the dangerous effects of foreign direct current to which d.c. track circuits in some communities are subjected. The above table is therefore of interest as it shows the application of alternating current as made to Dr. Robinson's invention of the closed track circuit.
Part IV
THE TRACK CIRCUIT IN GREAT BRITAIN AND ON THE CONTINENT
By T. S. Lascelles
No satisfactory records appear to have been kept as to the origin and development of track circuiting outside the United States, which renders it very difficult to arrive at any conclusions that could serve as a basis for a real historical sketch upon this interesting subject. In view of the fact that the Signal Section of the American Railway Association proposes to publish a memorial to the late Dr. William Robinson, generally regarded as the inventor of the closed track circuit and certainly the first to utilize it in the control of an automatic block system, the following brief remarks may prove of interest to the writer's fellow members of the Signal Section. It is not suggested that they are in any sense complete, as to make a complete survey would require considerable investigation. They really represent the writer's present general understanding of the subject and are open to such criticism and correction as anyone may be able to offer to them, in England or elsewhere.
There is no doubt but that track circuits were thought of and actually experimented with in England a great many years ago—probably as far back as the earliest American attempts—but the want of satisfactory records make it very difficult to decide on what actually took place. However, it is certain that the late W. R. Sykes, well-known throughout the railway world for his controlled manual block and other inventions, endeavored to use the track circuit in the sixties and that Bull, the inventor of the bull-headed rail employed in England for the chaired track universally found there, clearly had the idea of a track circuit in his mind, for he refers to it in a patent obtained in 1860. It was apparently in the early part of the sixties that W. R. Sykes fixed a track circuit experimentally at Briseton on the old London, Chatham and Dover Railway, and shortly after also at the Crystal Palace Station on the same line. The apparatus employed must necessarily have been rather primitive. In the seventies, track circuit was installed by him at St. Paul's station, also on the Chatham Railway. At that time very little was known about the track circuit theoretically and the construction of the relay was very different from our modern types. Sykes' relay completed the control circuit by the insertion of a contact point into a mercury trough. It was also, the writer believes, built on the solenoid principle. So far as is known it was not suggested at this time and at all events not attempted to make an automatic block system controlled by track circuits, such schemes for signaling of this type as were put forward being always based on the intermittent or track instrument control plan.
It must be remembered that the conditions obtaining in England, widely different from those seen in the United States, were not such as to give much encouragement to the development of automatic signaling, while over and above this, the English conservative nature always looked askance at automaticity in railway apparatus. Automatic signals, worked on a track instrument plan, were put into regular work on the Liverpool Overhead Railway in 1893, but it was not till 1902 that automatic signals controlled by continuous closed track circuits were to be seen in operation on an English main line railway. Before this, however, track circuits had made some progress, though not very much; the most important instance of its application was in the Kings Cross tunnels, just outside the London terminal of the Great Northern Railway, in the early nineties. This installation, which was used under none too favorable circumstances from the point of view of successful operation, proved to the English what the track circuit could do and heralded the day when its place in the safe working of railways should be better appreciated. By this time in the United States, largely under the influence of the pioneer work of Dr. Robinson, automatic signaling had made quite considerable progress and the potentialities of the track circuit had been fairly realized.
It may occur to Americans to ask why it was that progress in England was so slow and this is a question which cannot be answered by a single reason since a combination of circumstances was the cause. In the first place the older type of English signal officer was extraordinarily conservative regarding signaling practice of other countries as he had that peculiar type of contempt which generally comes from want of knowledge. Anyone who, like the writer, listened for instance to the objections brought forward by some of these men to controlled manual block, will know to what absurd lengths they could go in resisting improvements in working. Although this spirit, which has markedly diminished during the last 15 years, must have accounted to some extent for the slow development of the track circuit in England, there were yet some reasons of a more sensible kind which must be borne in mind. The English light weight four-wheeled freight car without air brakes was and still is a bother to the track circuit engineer because of the difficulty of getting a satisfactorily low shunt under all circumstances. Then again the Mansell disc wheel made it necessary to resort to bonding between the tire and the hub before a vehicle would shunt the track circuit at all and this was an expense to which the companies were loath to go, especially if they had or contemplated very few track circuits, though the use of even one circuit really necessitated the whole of these wheels being so treated. There was no great demand for automatic signaling, as the manual system was giving good results and was also cheap at that time, owing to the low wages paid to railway men. This and the other reasons just given combined to render the progress in England extremely slow.
Some of the First Installations
Nevertheless, in 1902 the British Pneumatic Railway Signal Company, who had in the previous year installed its first low pressure pneumatic interlocking at Grateley, on the London and South Western Railway, brought into use between that station and Andover an automatic block system controlled by continuous track circuits, the distance being about six miles. The signals were worked by low pressure air. The success of these systems led to the adoption of them shortly afterwards on the widened four-track main line between Woking and Basingstoke on the South Western, a distance of 24 miles. The Grateley-Andover installation has now been removed, not because it was at all unsatisfactory, but because it was felt traffic and other circumstances did not warrant its further employment. In 1905, Hall electro-gas automatic signals were brought into use on the North Eastern main line between Alne and Thirsk, a distance of 11 miles. In 1907, semi-automatic signals were installed between Pangbourne and Goring, a distance of 2¾ miles, four track, by the Great Western Railway to divide up a long manual block section and a few similar installations have been made on the Midland, the Great Central, the Belfast and County Down and other roads.
By this year, track circuiting had begun to be extensively used in England. The British Pneumatic Signal Company had installed a series of low-pressure plants near Manchester on the Great Central and track circuits were used throughout while the same thing had been done at Clapham Junction on the South Western. The Westinghouse Company had supplied the District Railway, London, with automatic signals and were actively engaged in fitting similar apparatus to the tube lines; they soon afterwards commenced work on the Metropolitan Railway.