Pros and Cons of the Trolley-bus
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Reasons for the Revival of Interest in this Means for Transport and How it Compares with the Petrol Bus
AN interesting paper on trolley-buses, or as the author, Mr. C. 3. Spencer, O.B.E., IVI.I.E.E., 31.Inst,T., prefers to call them, electric trolley omnibuses, was read before the Institute of Transport last Monday. The object of the paper was to discuss and render understandable, if possible, the reasons for the resurrection of a form of transport which, for a period, remained almost dormant
The author mentioned that the trolley-bus has also been given other descriptions, such as, the " tramwayman's last hope," and in a discussion on a paper read in 1930 it was described as a mongrel without pedigree and virtue.
In 1911, the trolley-bus was inaugurated in Leeds and Bradford. At that time the advent of this vehicle or the petrol bus was not considered to be a challenge to the tram but only as a means for transport where the cost of installing tramway track, electrical equipment, etc., was commercially prohibitive. The problem to be solved was to provide facilities where the possibilities of traffic were not very good.
Early Types of Trolley-bus.
The early types of vehicle were, however, somewhat clumsy and their riding qualities, as contrasted with those of the tram, were unsatisfactory, mud was splashed and certain earth tremors began to be experienced. The chief trouble was largely due to early designers not taking advantage of the knowledge even then available regarding petrol chassis and bus-body design.
About 1913 Bradford put into service vehicles built in its own workshops and of a lighter and sweeter-running type, but the roads of the West Riding of Yorkshire were mostly paved with stone setts or were of water-bound macadam, with the result that potholes and ruts soon developed, and on the setts riding was always bumpy.
In 1914 the development ,of the trolley-bus and the petrol bus was proceeding on parallel lines, but the war stopped the progress of the trolley-bus and encouraged that of the petrol bus, with the result that by early 1919 the petrol bus was far ahead and was more in public favour.
The early Continental types bore a striking resemblance to farm wagons. The first English types did not compare unfavourably with petrol buses of the same period, and in the absence of noise and odour they bad advantages, whilst roads, generally, were not suitable for either form, except in London, where the roads were better and rubber-tyred buses made more appeal at a much earlier date.
Fundamental Principles Attractive.
The fundamental principles of the trolley-bus were, however, so attractive to certain engineers that it was not allowed to be forgotten. Something was to be said in favour of a method of construction that utilized the most perfect motor that has ever been invented—the series-wound electric motor which gives maximum torque when starting. It is of simple construction and capable of 100 per cent. overload for several minutes without sustaining damage, whilst it takes advantage of a cheap and abundant supply of home-produced energy, making possible a sweet-running, noiseless, odourless and flexible Means for transport It was undoubtedly this which induced Mr. R. H. Wilkinson, transport manager at Bradford, to take up the development of the trolley-bus from the point where it had been dropped. Much credit is due to him for his courage in this respect. Birmingham, Wolverhampton and other undertakings soon followed his lead, Birmingham with a short tramway-route conversion, and Wolverhampton with ri more ambitious scheme which has resulted in the conversion of the entire tramway system to trolley-buses.
The change which has taken place in the public view during the past few years seems most remarkable, and the author can suggest that this is only attributable to the merits e)f the trolley-bus system. It must not be overlooked that, in most cases, these vehicles have replaced trams which were decidedly out of date. Ten years ago there B24 were 47 miles of trolley-bus routes open for traffic ; now approximately 256 route-miles are operated on this system and extensions are rapid. The growth has not been confined to this country. America has for long taken 'great interest in this form of traction, and in the U.S.A. 135 miles have been opened.
It is true to say that the modern trolley-bus is little more than an adapted petrol bus, the engine and gearbox having been removed, and an electric motor substituted with suitable control and electrical connecting gearing. The trolleybus designer is greatly beholden to the pioneers who have so wonderfully developed the petrol vehicle. He has taken advantage of the well-sprung chassis, efficient mechanical transmission, improved brakes and pneumatic tyres, and with the electric motor has been able to produce a vehicle giving fine acceleration and speed, without the drawbacks of the internal-combustion engine.
. Trolley-poles Not Quite Satisfactory.
Evolution. has produced nothing better, so far' than trolley poles, which, whilst a workable and reliable sehenie, cannot be described as entirely satisfactory, and, frankly, are the weakest point of operation. It is mostly in the direction of a simple current-collection method that further ,progress is desirable. If it were possible to transmit the electrical energy from the trolley wire to the vehicle by, say, a radio power-transmission scheme, the collecting gear could be eliminated and the overhead wires considerably modified. Here is an opportunity for some electrical genius. The author admits that he has not the faintest idea how this Utopian idea can be achieved, but if it proves quite ridiculous he has no doubt that something equally effective will be found.
The driving control gear is very different from pre-war days, the hand controller having been displaced by foot, thus allowing the driver to have both hafids free for steering. The adoption of one motor instead of two has improved the control, as the driver merely presses a pedal as a motorist uses the accelerator. The controller itself operates the contactors by means of a small relay current.
The Modern traction motor now weighs only 12 lb. per h.p., and by the introduction of commutation poles and heatresisting insulation, it is possible to abuse this unit to almost any extent without harm. Normally rated at 80 h.p., it can give 160 h.p. for short periods. Field shunting is done to a much greater extent than before, not with a view to more speed, but in the interests of economical working. What has wrongly been termed " super-saturation of fields" is becoming common practice. A motor has been designed which, with a fell field, gives little more than half the maximum speed, the rest being obtained by shunting, which cuts down resistance wastage considerably. The eiperiments of the London 'United Tramways show that a saving in current of 18 per cent. has been achieved, and the maximum required for starting has been reduced by 30 per cent.
Development of Regenerative Control.
Another development is the use of regenerative control. Compound motorsare employed, the current generated when braking being returned to the trolley wire and distributing system and, therefore, utilized for the operation of other vehicles. On hilly routes the saving is claimed to be 2025 per cent.; in addition there is less wear of brakes.
There is an electrical trouble which caused some concern. It has resulted in a flood of complaints of inter-: ference with the reception of bnoadcasting. but with the co-operation of the G.P.O., the B.B.C., and the trolley-bus engineers, the interference has practically been eliminated by a very simple meaus, including the introduction of choke coils which can tune out the electrical disturbance, so far as London stations are concerned.
Before replacing a tramway system by any bus system, careful consideration must be given to the obligations, statutory and otherwise, of the tramways to be replaced. The peak-load traffic in relation to the slack traffic is, in
many cases, exceptionally high. On one Metropolitan route, between 7 a.m. and 8 a.m., 5,500 passengers per hour are carried; after that, and until 4 p.m., the number is 500-800 per hour.
Until recently both trolley-buses and petrol buses were limited to 54 passengers. Thus it has been necessary to run 25 per cent. more car-miles with a trolley-bus, but the traffic has increased in like ratio.
Under like circumstances, the general traffic running costs should be approximately the same for the two types. The trolley-bus has the advantage of superior acceleration, assisting schedule building and giving a higher average speed. General administration costs would probably be higher than with petrol vehicles. The electrical equipment is a rateable hereditament ; this the petrol bus escapes.
As regards power, the comparison is in favour of the
trolley-bus. On L.U.T. vehicles not converted to field control, the consumption is 2.65 units per mile, which at .794. per unit, gives .2.09d. The equivalent figure for a petrol bus with petrol at Is, per gallon and 5 m.p.g. would be 2.4d. per mile. More than 60 per cent, of the cost of petrol is by way of taxation, but how far the duty on petrol can fairly be considered as a legitimate charge against the petrol bus is hardly a matter that can be
discussed by the author. • It is important that current should be cheap and the supply abundant if encouragement is to be offered to the
power station. It is short-sighted to keep the price of current high. The trolley-bus uses 100,000 units per annum—operating seven days of 18 hours per week, and usually has a load factor of over 40 per cent. The relative total operating costs for similar types of trolley-bus and petrol bus for the past year were : trolley bus, 12.21d. per vehicle mile ; petrol bus, 12.83d.
The great need is for a vehicle of larger capacity if the trolley-bus is to replace the tram. There is little to be said in favour of the trolley-bus on thin traffic routes. The petrol vehicle is undoubtedly the most suitable proposition in circumstances where the traffic does not require relatively close headways.