Popular Science Monthly/Volume 74/March 1909/The Electric Operation of Steam Railways
|THE ELECTRIC OPERATION OF STEAM RAILWAYS|
By Professor J. B. WHITEHEAD
THE JOHNS HOPKINS UNIVERSITY
THE possibility of operating all classes of steam railway service by electricity has been demonstrated beyond question. Heavier trains may be hauled at higher speeds and with greater comfort to passengers, and electric locomotives may be built which surpass in power any steam locomotive which may be constructed. Two of the most important railway systems entering New York city are now operated entirely by electricity for distances between twenty and thirty miles from Grand Central Station. The Pennsylvania Railroad Company has recently closed contracts to the extent of $5,000,000 for the electric operation of its tracks between Newark, N. J., through the Hudson and East River tunnels, to Jamaica, L. I., where it will join the tracks of the Long Island Railroad, which for some time has been operated electrically.
The total steam railway mileage in this country aggregates about 220,000 miles of line but notwithstanding the important projects mentioned above, and others of less note, it remains a fact that only about 1,000 miles of railroad, formerly operated by steam, have been transformed to the use of electricity as motive power. The question then arises as to what conditions have started the present development and as to whether this beginning will extend itself in general degree to the large trunk line systems of the country. It is not sufficient for the engineer of to-day to demonstrate the physical possibilities of a project, but he must go further, and justify it on the grounds of business advisability and economy. If, then, it be asked why have steam railroads begun to substitute electricity as motive power, the answer is to be found in two broad reasons. The first of these is, that in some instances the use of electricity is the only possible way of handling the traffic. The second reason is the invariable one, in this commercial age, for all engineering enterprise—that it pays.
The development of the engineering methods by which the electrical operation of railways has been made possible is largely due to the first of the reasons mentioned above. Beginning with the electrification of the Mt. Royal Tunnel of the B. & O. Railroad, in 1896, there have been an increasing number of tunnel and terminal projects which have made use of the possibilities of electric operation in the way of increased traffic and freedom from smoke and gases of combustion. One conspicuous instance, the Grand Central Terminal in New York city, illustrates the typical limitations of tunnels and terminals which have rendered electric operation necessary. In 1903, an act of the New York Legislature was passed providing for the operation before July 1, 1908, of all trains into Grand Central Station by some form of motive power not involving the combustion of fuel in the motive units. This action was aimed directly at the elimination of smoke and gases in the tunnels leading to the terminal. The results of the adoption of electricity have in this respect entirely justified expectations. Passengers may now occupy observation platforms in passing through these tunnels which were formerly notorious for their danger and discomfort.
There was, however, an additional reason why it was necessary to adopt a motive power other than steam in the New York terminals. Traffic into the Grand Central Station is limited by the number of tracks in the tunnels. The minimum three-minute headway between trains operated by steam fixed the maximum traffic at forty trains per hour each way. The capacity of the terminal with this limitation of service was taxed to its utmost and some relief for the increasing traffic was imperative. Owing to the improved conditions of electric operation, trains may be run on a two-minute headway or less, thus increasing the station capacity by more than fifty per cent. The conditions in the New York tunnels are typical and other conspicuous instances of similar installations are those of the B. & O., at Baltimore, the St. Clair tunnel of the Grand Trunk Railway and a three-mile tunnel on grade on the Great Northern Railway. The Illinois Central Railroad is about to electrify 325 miles of track, comprising the approaches to its Chicago terminals.
The elevated lines of New York city are an additional instance of the necessity of adopting some other system than steam in order to increase the capacity for traffic. The continued growth of the population of New York city has far surpassed that of the traffic facilities for transportation within the city. As measures for relief the elevated and surface lines were equipped with electricity and in addition the subway system was constructed. Within three years following the adoption of electricity, the capacity of the elevated lines in car-miles per day was increased 331⁄3 per cent, and this in spite of the facts that the subway system had inaugurated during this time a service furnishing over 75 per cent, that of the steam elevated and that the surface lines showed little or no decrease. During the two years ending 1906 the increase in passengers on all the lines of New York city numbered more than 114,000,000, which is about 75 per cent, of the ultimate capacity of the subway system. In order to handle this continuously increasing demand it has now become necessary to consider the construction of additional subways.
Returning to the second of the reasons given for changing to electricity, the general statement that it will pay to electrify a steam railroad may not be made without important qualifications. It is admittedly true for the majority of steam roads of any considerable size and density of traffic that the operating expense would be substantially reduced by electric operation. Figures showing that this saving, together with the returns from increased business, is sufficient to offset the interest charges on the necessary capital are still few. Such figures have, nevertheless, been given for existing roads on which the transfer to electricity has been made. On the other hand, on railroads operating light trains and comparatively infrequent traffic, it is at once evident that there would be little if any saving in operating expense in changing the motive power. Much of the economy possible under electric operation results from the combination of all the locomotive boilers and engines into a central power plant. It is obvious that when the number of such locomotives is small that the cost of the power plant and the motor equipments may far outweigh the economies obtained. There is, however, an intermediate class of road, many instances of which have been equipped electrically, in which the saving in operating expense, together with the usual increase of business following the electric installation, are looked to for a reasonable return on the capital invested. The enormous amount of capital represented by the steam equipments of existing railroads, which can not be applied to the new equipment, is the most serious obstacle to the general adoption of electricity as motive power. It will only pay to electrify in those cases where the economies in operation and the increase in business will outweigh the charges on the new capital necessary.
The public will invariably drift to an electric rather than a steam route between given points. Moreover, when a steam road is paralleled by electric service, not only does the latter take the bulk of the traffic, but the traffic itself increases in volume. Further, when a sparsely settled section is penetrated by an electric road, population and consequent business follow promptly. These facts are now matters of common observation. One extreme example will indicate the lengths to which these facts may go. A steam road in the middle west was paralleled by an electric line; the latter took away over fifty per cent, of the steam traffic and increased the total traffic fifteen times the original amount within seven years. If we look for the reasons for such advantages in absorbing and promoting traffic we realize that electric travel is faster, more frequent and more comfortable. It provides freedom from smoke, better ventilation, easy regulation of light and heat and in fact travel in many instances is actually a pleasure.
While the public is appealed to as cited above, the operating and transportation departments of the railroad are equally appealed to by the methods afforded under electric operation for handling the resulting increase in business. Present day steam service may be divided into three broad classes: (1) Suburban and terminal; (2) long haul passenger and express and (3) freight traffic. The advantages of electricity as motive power in all three of these classes of service are found in the possibilities of obtaining more mileage and hauling capacity from the equipment, the operation of more trains on the line at one time and better operating conditions and consequent reliability.
Figures have already been given showing the increased train capacity of the several electric installations in and about New York city and many other similar instances might be cited. These results are largely due to the fact that an electric locomotive or train operates at a higher schedule speed than is possible under steam. The elapsed time of a suburban train between stops depends principally on the rapidity with which it attains its maximum speed. The rate at which it reaches this speed, that is, the acceleration, depends on the value of the pull exerted by the motive power. During the period of starting the greatest draw-bar pull is required, since during this time the inertia of the mass of the train must be overcome. After reaching a maximum speed the only forces to be overcome are those of frictional resistance of the track and the air. In a steam locomotive the greatest draw-bar pull being required at starting, steam is admitted to the cylinders throughout the full length of the stroke. The demand on the boiler per revolution is, therefore, greatest at this time. No loco-, motive can, on the average, exert a greater pull than 25 per cent, of the weight carried by its own driving wheels, for beyond this figure the wheels will slip on the track. The boiler capacity, therefore, is designed to give no more steam than that demanded by this value of the pull at starting. A steam train, therefore, does not utilize the weight of its own cars as a means of increasing its grip on the rails. In a multiple unit electric train, motors are placed on each car, thus utilizing the weight of the entire train for frictional adhesion to the rail. By electric control of the motor switches all the motors may be operated simultaneously by one man at the head of the train. By this system the draw-bar pull per ton of train may be increased from 2.5 to 4.5 times that for steam and the rate of acceleration is only limited by the comfort of the passengers. As a direct result of this the schedule speed is increased;, the headway between trains is reduced and more trains may be operated on the line. By the use of electric locomotives in terminals for switching service great economies are effected. Since the electric locomotive operates in either direction and takes its entire power supply from the trolley or third rail, much useless mileage of locomotives in going to and from the turn-table, the water-tank and the coal-chute is avoided. The New York Central has already reported as a result of tests a net saving of 21 per cent, on the cost of switching service and 16 per cent, in the ton mileage of switching locomotives.
For long-haul passenger and express service rapid acceleration is not so important, but the maximum speed becomes the determining factor in a fast schedule. For any type of motive power the draw-bar pull is greatest at starting and falls to lower and lower values as maximum speed is approached. Consequently, for this class of service, large initial effort is not so important as large effort at high speed. In this respect the electric motor has a great advantage over the steam engine. Since the boiler of the steam locomotive is proportioned to the maximum demand which it can generate at starting, corresponding to the grip which it has on the rails, at higher speeds the steam must be cut off from the cylinders at a less and less fraction of full stroke, for otherwise the boiler can not supply steam fast enough and still maintain its pressure; thus the total tractive effort, which depends on the proportion of a revolution during which steam is admitted to the cylinders, is reduced as the speed increases. While the tractive effort of the electric motor also decreases somewhat with the speed it does not do so nearly as rapidly as that of the steam locomotive. As a consequence, a given weight of train can be handled faster by electricity than by steam or a heavier train may be hauled at a given maximum speed. Again, the safe limits of speed are much higher in electric operation. The rotative effort is uniform in a motor, while that of a locomotive is intermittent and accomplished through the medium of heavy reciprocating parts. The moving mass of these parts as the speed increases tends to lift the locomotive from the track and pounds the rails with a blow which in many instances has been sufficient to cause derailments. The limiting speed of steam trains is about 80 or 90 miles per hour, while speeds of 130 miles per hour have been reached in tests on electric trains.
The advantages of electricity for freight traffic are most apparent on long single track lines with heavy grades and mixed traffic. The length of the freight train of to-day is limited by the draw-bar pull of the locomotive which is in turn dependent on the locomotive weight. and by the schedule speed. Speaking generally, longer trains and hence fewer trains on the line at one time, are to be had only at great sacrifice of speed. The longest freight trains weigh from 2,000 to 3,000 tons and are only operable on level track. On reaching mountain grades, such trains have to be broken into two or three parts, which, therefore, on single-track roads increase the number of passing points and subsequent delays, thus rapidly shortening the headway between trains and filling the line to its capacity. Schedule speeds on such grades now average about ten miles per hour. The operation of two or more locomotives in a train is not satisfactory, owing to the impossibility of securing simultaneous cooperation of the several motive units. As already stated the tractive effort at high speeds is much greater for the motor than for the steam locomotive; hence, in the case of electric operation, the limiting weight of the train on grade is higher, also the schedule speed may be largely increased by the use of double or triple headers. This method of operation is perfectly possible under electricity by the system of multiple control, already mentioned, and the length of a train is limited only by the strength of the draft gear. This limit would disappear if all freight cars could be equipped with a simple standard cable, enabling the placing of an electric locomotive in the middle or at the end of a train. This cable would be necessary to secure the simultaneous operation of the several locomotives.
A few comparative figures bearing out the above facts of the possible methods of increasing railway business are not without interest. A typical western freight locomotive, weighing with its tender 165 tons, can develop continuously a draw-bar pull of 25,600 pounds, up to a speed of 15 miles per hour. An electric locomotive, weighing 100 tons, can develop this value of pull, up to a speed of 37 miles per hour. Another similar type of electric locomotive gives 56,800 pounds, up to 23 miles per hour, and still another 8-motor type can develop 113,600 pounds draw-bar pull up to a speed of 23 miles per hour.
A late type of Mallet compound locomotive, weighing 300 tons, can develop continuously 2,180 horse power at its driving wheels. A New York Central electric locomotive can do the same and weighs only one third as much. The cost of each locomotive is about the same. It may be noted that 200 ton-miles are saved in every locomotive mile if the electric locomotive is used instead of the steam locomotive. At 40 cents per locomotive mile and 100 miles per day the saving is $40 per day or about $15,000 per year. The saving on this account alone would in two years pay for the electric locomotive. Another type of Mallet locomotive, weighing with its tender 250 tons, can haul a train weighing 330 tons up a 2.2 per cent, grade at 15 miles per hour. A 100-ton electric locomotive can haul a train of 800 tons under the same conditions. The total train weights are thus 580 and 900 tons and the electric locomotive weighs 100 tons less than the steam locomotive, resulting in the consequent saving in the ton mileage of dead weight.
The operating conditions and the reliability of service are improved in all classes of traffic by the substitution of electricity. The construction of the electric locomotive is far simpler. The steam locomotive comprises fire box, boiler, steam engine and facilities for handling coal and water. The electric locomotive, on the contrary, consists only of the electric substitute for the engine and this substitute has no reciprocating parts. There is consequently less wear and tear and less likelihood of derailment and broken rail. The fire box and boiler are absent as sources of danger in a collision, as are also apparatus for steam or fire heating and oil or gas lighting. Signals are clearer in the absence of smoke and automatic signals are possible, though as yet they are little used. The control of power to trains in sections or blocks is also possible. The number of car miles per train-minute of delay has been nearly doubled on the elevated lines of New York since the electrical operation was inaugurated. Less time is required for clearing and despatching trains, water and coal stops are obviated and less attention is required for light and heat. The electric locomotive is always ready, requiring no time for firing.
As against these several advantages in operating conditions and reliability, there are several disadvantages. The supply of power to all trains from one power house is objectionable from the standpoint that an accident at the power house may stop all trains. Whatever may be said of the steam locomotive in its comparison with the electric motor, the locomotive is self-contained. This danger under electrical operation is minimized by a thorough subdivision of all the power house apparatus. This method of subdivision, however, is not so readily possible in the transmission and conducting systems leading power to the trains and accidents to this portion of the equipment constitute one of the most serious menaces to the continuous operation of an electric railroad. The presence of the third rail or trolley and the transmission line throughout the right of way is in itself a certain source of danger. In a collision the danger of a fire from a third rail in some measure offsets the similar danger from a locomotive fire box. The danger from this source, however, has been overestimated, and the danger of shock from a high voltage trolley is practically eliminated by the modern methods of suspension. These methods consist in supplementing the actual trolley conductor with one or more steel cables for increasing the tensile strength of the overhead construction. The thorough grounding or connecting to the rail of all the supports of the trolley wire ensures that even in the unlikely instance of the breaking of the overhead construction the wire will have no voltage when it reaches the ground. So reliable has this method of suspension come to be regarded that it is now often used for crossings of telegraph, telephone and transmission wires in place of the usual cradle or network of wires stretched between the two lines. The values of voltage now advocated for railway and transmission work have caused considerable criticism and opposition. This is probably due in large measure to the long standing figure of 600 volts for trolley service; this figure, however, is fixed by the character of the direct current motor and not by any consideration of possible danger from shock. A further source of disturbance by electrical operation is the interference by electrostatic and electromagnetic induction between the transmission conductors and the telegraph and telephone lines in the vicinity. Methods have been developed, however, and are at present in use by which such disturbances are prevented at slight cost.
A decrease in the operating expenses has already been stated as one of the means by which electric operation may be made to pay. The operating expenses of an average steam railroad may be roughly divided as follows: Maintenance of way 21 per cent., maintenance of equipment 19 per cent., conducting transportation 56 per cent., general expenses 4 per cent. Considering these items under electric operation the greatest saving is effected in the item of conducting transportation, which includes the cost of coal. The steam locomotive consists of a boiler and engine. For obvious reasons neither is as efficient as the same apparatus of a stationary type. The same amount of coal in a locomotive boiler will evaporate only about two thirds as much water as in a stationary boiler. The average steam consumption of a good locomotive engine is about 30 pounds of steam per horse power hour developed; turbo-generators are now guaranteed for a consumption of only 15 pounds of steam per electrical horse power at the switchboard. As offsetting these marked advantages it is necessary to consider the electrical losses in the transmission system and in the motor equipments. Speaking roughly, 75 per cent, of the electrical energy supplied by the switchboard is available at the wheels of an electric train for tractive effort. These figures indicate that an electric locomotive requires less than one half the amount of coal used by the steam locomotive giving the same horse power output. Further than this, it has been estimated that for every hour that a locomotive is standing idle, with steam up, 400 pounds of coal are burned. The excess of useless mileage and the excess ton mileage owing to the greater weight of the steam locomotive have already been noted, and are also causes for excess coal consumption. As opposed to these, there is the light load coal consumption of the power station. The final value of the balance in coal saving will depend on the proportion of time in which the power station operates to its full capacity. Based on careful comparative tests of steam and electric locomotives the engineers of one of the large installations already mentioned have announced that the electrical operation of the former steam service is being handled with the consumption of only 60 per cent, of the amount of coal, resulting in a saving of nearly $350,000 per year. Figures have been published showing that the Manhattan Railway under steam operation secured about 1.5 ton miles to a pound of coal; under electric operation this figure has increased to 3.85. These and other careful estimates indicate that in the general electrification of through railway lines a saving of 50 per cent, in coal consumption may be effected. It is to be noted, however, that the cost of fuel alone is only about 12 per cent, of the total cost of operation; therefore, a saving in this respect would be only 6 per cent, of the total operating expense. In the kindred items of firemen, roundhouse men and other expense peculiar to the steam locomotive a further saving of about 5 per cent, is possible. It is interesting in this connection to consider the effect of this fuel saving on the total coal supply of the country. The fuel consumption of all the locomotives in this country in 1905 was about 52,000,000 tons, which was about one eighth of the total coal production of that year. The total coal consumption, therefore, would be reduced by about 7 per cent, if all the railways in the country were electrified. This does not appear to be a very important reason why railways should electrify; but with trans-Atlantic liners burning 5,000 tons of coal per voyage and the end of the coal supply of the state of Ohio in sight within 25 years, any influence tending to check coal consumption must soon assume importance.
The repairs to steam locomotives amount to about 8 per cent, of the total operating expense. The repairs to an electric locomotive amount to far less. The greater simplicity of the electric locomotive has already been noted. There are now available plentiful data based on experience indicating that the above figure of 8 per cent, may be reduced to the neighborhood of 2 per cent. An additional saving in the maintenance of track and other less striking items offsets the repairs to track bonding and overhead construction and leaves an additional saving in favor of electric operation of about 3 per cent. The aggregate of the above economies in operating expense amounts to 20 per cent., which should be readily available by any of the large railway systems in the transformation to the electric method of operation.
Considering further the several pioneer installations of electric service, we find that they differ materially in their characteristics and there are several so-called systems at present available. The early development of the electric railway for operation in cities was entirely dependent on the use of the direct current motor as the only motor available. This motor had been developed in spite of the fact that the earliest electromagnetic generators were of the alternating current type. The value of alternating currents was not appreciated, however, as the principles of transformation and their value for transmission were not understood. The high degree of perfection to which the direct-current motor has been developed naturally led to its use for railways as city lines were extended, and this tendency has resulted in the enormous mileage of suburban and interurban electric railways. This tendency was aided by the development of the rotary converter which permitted the transmission of power by alternating currents and its conversion to direct current for supplying the trains. The direct current motor operates at about 600 volts and thus fixes the value of the voltage on the trolley or third rail. The voltage being fixed, the total energy at a car is proportional to the current. Thus, for light cars and infrequent traffic, the loss in the trolley and feed wires, due to the passage of current delivering energy to the car, is sufficiently small to allow operation at comparatively long distances from the point of generation. With increasing size of cars or trains the points of supply must be brought nearer together and be made of greater capacity. In the case of the New York Central installation, the average distance between such stations is four miles. Each of these substations contains transformers for reducing the voltage from the transmission line and rotary converters for changing the alternating to direct current. The amount of current taken by a train on this system may go to very large values and this necessitates large trolley and feeding conductors when the traffic increases in volume. Under this system the feeding conductor may be either trolley or third rail and the collecting device, the trolley wheel or third rail shoe. The latter must be used when the currents are of large value.
With increasing length of line the cost of sub-stations and feeders in the direct current system becomes prohibitive. This has lead to the development of alternating current systems, in which the energy is generated, transmitted and delivered to the car at voltages as high as 15,000, with consequent reduction in values of the necessary current. Theoretically, the reduction in the size of conductors necessary to carry the current is inversely proportional to the square of the voltage. While certain characteristics of the alternating current system reduce this theoretical value quite materially, the gain in this respect is nevertheless enormous, and the distance between feeding points increases to between thirty and fifty miles, depending on the density of the traffic. The trolley wire alone is often the only feeding conductor required. Further, the apparatus in the sub-stations in these systems comprises stationary transformers only which require no attendance. Two conspicuous alternating current systems for railway operation have been developed. The single phase system, which has been almost the only alternating current system used in this country, and the three-phase system, which has met with some favor in Europe.
The single-phase motor has the same characteristics and operates exactly as the direct current motor and may in fact be operated by direct current—a fact which constitutes one of its greatest advantages. It is, however, heavier for the same output and since it, too, operates at low voltage, a stationary transformer is required on the car or locomotive to reduce the high trolley voltage to the value required. This necessitates a heavier and more expensive motor equipment than the direct current system and acts as an offset to the saving effected in feeding conductors and sub-stations. In this system the feeding conductor is the overhead trolley with catenary suspension and the collecting device is the sliding trolley or pantagraph which is necessary for very high speed and permissible by reason of the low values of current required.
The three-phase system owes its principal value to the fact that the speed variation of the motor is very small throughout its full range of tractive effort. As already stated, the tractive effort of the direct-current and single-phase motors falls off with increasing speed, though not so rapidly as that of the steam locomotive. Owing to this advantage, the three-phase locomotive can maintain its high speed independently of the grade. It operates without transformers on the car with trolley voltages up to 5,000 and in coasting it returns power to the line automatically, its motors acting as generators. It is, however, heavy per unit of output and the system requires two trolley wires and is not adapted to operation on the direct-current installations to be found in many terminals. It has been adopted for one installation in this country in which it is desired to increase the schedule speed on a long mountain division.
In this country the best engineering opinion seems to have united in thinking that the single-phase system is the one best adapted for future application to steam railways. This system is as yet only four years old, yet there are at present over 1,000 miles of railways in the United States operating under it and in this aggregate there are at least five railroads formerly operated by steam. The system has proved most successful in operation, although the first six months' operation of the New York, New Haven & Hartford Railroad have developed so many unforeseen troubles, when applied to such a large enterprise, as to bring upon it much adverse criticism. On the other hand, the high degree of perfection to which the direct-current system has been brought, the greater capacity of the motors of this system and the enormous mileage already installed in tunnels and terminals have resulted in a strong advocacy of this system. Speaking generally for motors of equal weight, that of the direct-current system has 25 per cent, more capacity than that of the alternating-current system. The equipment of a high speed interuban car having four motors of approximately 100-horse-power capacity, will weigh under direct current system 22,500 pounds and under the alternating system 32,000 pounds, or nearly 50 per cent, excess over the direct-current equipment. For the entire car, however, the excess weight would be only about 12 per cent. The excess in cost would be about 35 per cent. In the case of locomotives the excess weight of the alternating-current equipment is even greater. The New York, New Haven & Hartford alternating locomotive has about the same weight as the New York Central direct-current locomotive, but if compared on the basis of maximum tractive effort the former weighs twice as much. The two locomotives are, however, designed for different service and the comparison is much more favorable to the alternating-current system if based on the continuous capacity. The cost of each of these locomotives is about the same.
Taking a broad view of the situation at present, we find that the direct-current system is already installed and continues to be favored for dense, short-haul traffic, such as is found in city terminals and tunnels, and short suburban service. This is largely due to the greater familiarity with the direct-current motor, to its greater capacity and less cost. It is admitted, however, that this system will not do for through traffic over long distance. The single-phase system possesses marked advantages for long haul, express and passenger service on account of the great saving effected in line conductors and sub-stations. It has the great additional advantage that it can operate on direct currents also and may, therefore, enter terminals already equipped with direct current. There is every indication that the operation of steam railways by electricity will be rapidly extended within the next few years. It appears probable that the single-phase, high-voltage, alternating-current trolley will be used and that for some time direct current will continue to be used in terminals. The tendency, however, will be to abandon direct current in terminals, substituting the high voltage trolley throughout.
The process of change to electricity, however, must necessarily be gradual. The necessary capital investment must be provided for and this will probably be accomplished in any large instance by doing the work piece-meal and charging the cost to renewals. Methods for handling freight traffic have not yet been thoroughly developed. Much freight hauling is done by electricity, but before the bulk of traffic of a through line can be handled some method of multiple operation must be devised for freight trains and the work must be experimented upon by applying the methods at present indicated, to some large project. The standardization of electric railway apparatus is one of the greatest necessities of the present situation. No extensive system would care to operate its trains without the possibility of the exchange of cars with neighboring systems and until railway engineers are agreed as to the fundamental questions of frequency and methods of train control it is probable that no large project will be put in hand. A further opposition to be met is the mass of present-day, steam-railway methods and prejudices. The steam railway has a long history and each system has its highly-trained corps of operating engineers. Electrical operation introduces many new points of view, old dangers disappear and new precautions have to be taken. Besides these matters, there are various less important disturbances to steam practise which will have to be provided for, among the most serious of which are the clearances of the third rail and trolley at crossings and at overhead structures; the clearances on draw-bridges and the methods of leading currents through such bridges; new splice bars to accommodate rail bonds and the telltale for notifying a brakeman on top of the car of a low bridge ahead. It seems probable that the next step in this development will be the progressive equipment of a complete system involving through traffic over long distances, with its attendant feeder and branch lines. When such a system is once installed and the minor difficulties above enumerated developed and overcome, a rapid application of electricity for steam operation will follow.