The Trackless Trolley System in Great Britain.

Progress, Volume VI, Issue 9, 1 July 1911, Page 725

The Trackless Trolley System in Great Britain.

During- the past twelve months great efforts have been made to introduce into England the system of trolley traction without the use of rails, which has been installed in a number of Continental cities, but although a number of municipalities applied to Parliament in the session now drawing to a close for the necessary powers, these were not granted. Indeed in some cases, the proposed powers were withdrawn from the bill before the committee stage was reached. Nevertheless, the Railless Electric Traction Co., Ltd., was formed, and as the result of having examined all the systems at present working on the Continent, the Company have decided upon designs which it is anticipated will meet the probable requirements of authorities here and at possible alteration. Moreover, inasmuch as the railless feeder lines of this character will usually commence at some distance from the tramway carsheds, it is desirable that the railless vehicle, when coming from or returning to the car sheds, should be able to make use of the existing line equipments of the tramway. These conditions require that the trolley head should be of the usual under-funning type, carried .at the end of a rigid boom and kept in , contact with the overhead conductors by Raising springs in the trolley base. Another essential condition is that the trolley head should remain in contact with the overhead conductors under all conditions of service, and should permit of sudden and wide diversions of the car on either side of the entire of the centre lines of the wires. It is necessary, at the same time, to overcome the prejudices, if any,

of tramway managers and engineers. An experimental line has been installed at Hendon, on the outskirts of London, by arrangement with the Metropolitan Electric Tramways, Ltd,, who are running the car, which has been built by the Railless Electric Traction Co., Ltd. The Company worked upon the assumption that railless traction lines in this country would be extensively employed as feeders to existing tramway lines, and that these extensions may themselves afterwards be converted to tramway lines, when the traffic has developed sufficiently to justify the extra cost of rails. It is therefore requisite that the overhead equipment should be of such a character as will be equally serviceable to either system of traction with the least speed. It as apparent that this condition would not be fulfilled by the ordinary swivelling trolley base, and subsequent experiments have demonstrated the correctness of this conclusion. In order to meet the prescribed conditions in a satisfactory manner, a special trolley base has been • designed in which, besides the usual raising springs, there are additional springs working in ' a horizontal plane and controlling the pivot of the trolley base in such , a manner as to relieve the trolley wheel of excessive side pressure against the trolley wire, even when the car is running at some distance from the wires. With this attachment the head travels freely under the wares and without appreciable side pressure, at whatever angle the pole may be trailing, from 90deg. on one side to 90deg. on the other. .

A point, to which considerable attention had to be devoted, was the absolute prevention of any metallic portion of the car becoming alive, as the simple tramway expedient of binding all metallic parts to each other and to the underframe, whereby they are necessarily maintained at earth potential through the medium of the wheels and rails, is obviously not applicable to a vehicle shod with rubber tyres. Continental engineers have so far ignored this danger and have placed full reliance upon the insulation of the motor circuit, but it is recognised that tramway engineers in this country will require some means of obviating or minimising a danger from which tramcars are effectually protected. The Company claims to have overcome this danger absolutely by a patent triple trolley head and triple line hanger. These designs require that the overhead line should comprise three trolley wires, of which the two outer wires are positive and the centre wire negative. Three trolley wheels are mounted on a single rotatable head, the two outer wheels, which are connected together making contact with the outer or positives wires, and the inner -wheel with the centre or negative wire. To ensure that the inner wheel may' not, under any circumstances, come in contact with either of the positive wires, the negative wire is supported at an elevation of several inches below the positive wires, and the negative trolley wheel is mounted in a corresponding position relative to the outer wheels. The three conductors are supported by a triple hanger, which may be made either in one piece or in three separate parts bolted together. If it is decided to equip the route as a tramway, it is only necessary to undo the bolts in the hanger, remove the centre portion with the centre wire, and slide the two outer portions with their

trolley wires to any desired position upon the span wire.

In the triple trolley head a pair of wheels is used for making contact with each of the positive trolley wires. Each wheel is capable of a slight axial movement, and the pivot from which it is mounted is free to move vertically under the motion, of a coiled spring. A distinctive feature of the triple trolley head is the rigid base. The trolley pole is made up of two separate poles which form two sides of a parallelogram, of which the two ends are the trolley base and the head, respectively. The head, therefore, always remains parallel to the base, and in consequence, approximately parallel also to the surface of the roadway. By this device the stability of the head is enhanced, and it is found that variations in the actual and relative heights of the trolley wires are more easily met by the coiled springs under each wheel, than by allowing to the entire head a rocking motion about each horizontal axis. By a socket and plug attachment the head may be converted into the usual single pole trolley head, which can be used for running the trackless car along the route of an existing tramway line. The return circuit is, in this instance, provided by the rails, to which connection is made by a pair of slippers, which are suspended from .the rear platform of the ear and travel in the groove of the rails. The suspension is effected in such a manner as to permit the railless car to deviate several feet on either side of the centre line of the track. An alternative design has been prepared in which two trolley wires only are used, but as this does not remove the possibility of the metal parts of the ear becoming alive, provision has been made for audible notification of the existence of this condition of things. As a matter of fact, the two-wire system is in use on the experimental track. In this design one wire is positive and the other negative, and the positive and negative trolley wheels are mounted as before on a common rotable head.

The framework of the car, instead of being directly attached to one of the trolley wheels, is brought to the middle of a single pole double-throw switch, by which it can be connected at will, to either one or the other trolley wheel. A polarised relay is mounted on the car, one coil of which is energised by the trolley circuit, the other by a small storage battery. When the single pole switch is in the correct position to connect the framework of the car to the particular trolley wheel which is at that instant in contact with the negative conductor, the relay is inoperative. But should the polarity of the trolley wires be for any cause reversed, the relay instantly brings into action an electric hooter mounted in the front canopy of the car.