Encyclopædia Britannica, Ninth Edition/Tramway

by Thomas Codrington

TRAMWAY.Originally a tramway signified a wheel track laid with timbers, and afterwards with iron plates, having a flange on the inner edge by which wheels of the ordinary sort were kept in the track (see Railway). The introduction of the flanged wheel and edge rail caused tramways to be superseded by railways, but not until many miles of tramroads had been laid and successfully worked in various parts of the United Kingdom. Although the name is sometimes given to a light railway, by a tramway is now generally understood a street railway, constructed so as to interfere but little with the ordinary traffic, on which vehicles having flanged wheels are propelled by -animal or mechanical power. Tramways in this sense originated in the United States.

A street railway for passengers was laid in New York in 1832, but it was soon removed on account of the accidents caused by it. In 1852 a French engineer, Loubat, revived tramways in New York, and they were soon afterwards laid in other American cities. A short line was also laid in Paris in 1853. The rails used were of wrought-iron, 5 inches wide, having a groove for the flanged wheels of the cars If to 2^ inches wide and 1 to 1| inches deep (fig. 1). To lessen the inconvenience to ordinary traffic occasioned by this rail, the " step rail " (fig. 2) was introduced, consisting of a flat surface 3 to 5 inches wide, which can be used by ordinary wheels, and a raised tread on the outer side 1 inch higher and If inch wide, on which the flanged wheels of the cars run.

Fig. 1 Fig. 2 This form of rail is still very general in America, and is a good one for the tramways, though not for the general public. In 1858-9 Train, an American, endeavoured to obtain an Act of Parliament authorizing tramways in London; failing in that, he laid tramways, by consent of the road author ity, first in 1860 at Birkenhead, and soon afterwards in London. The rail laid at Birkenhead had a step of f inch between flat surfaces 3 inches and 1J inches wide. That laid in London was narrower, with a step of half an inch, but the slippery flat surface and the step of the rail caused serious inconvenience and numerous accidents to carriages, and the tramways were removed in a few months, after one of them had been successfully indicted as a nuisance. In Birkenhead, in spite of complaints of the inconvenience caused to the general traffic, the original rails remained until 1864, when, after a short length had been laid as an experiment with a rail of the grooved section now in general use (fig. 3), the whole of the tram way, several miles in length, was re-laid with it. The tramway was subsequently indicted as a nuisance, but the trial resulted in a verdict in favour of the grooved rail. In 1868 an Act of Parliament authorizing the construction of about 6f miles of tramways in Liverpool was obtained; and in 1869-71 Acts for 61 miles of tramways in London were passed, and were soon followed by other Acts for tramways in Glasgow, Dublin, Edinburgh, and other provincial towns.

Tramways Act.In 1870 the Tramways Act was passed, enabling the Board of Trade to make provisional orders authorizing the construction of tramways in Great Britain, with the consent of the local authorities, and giving considerable powers for regulating their construction and working. By the Act the gauge, unless otherwise prescribed by special Act, is to be such as will admit of the use of carriages constructed for use on railways of a gauge of 4 feet 8| inches. Tramways for which Acts had been previously obtained were of 4 feet 8 inches gauge, to comply with a standing order intended for railways, and not to make them available for railway rolling stock, which the narrow groove of an ordinary tramway rail will not admit. There is reason to think that a narrower gauge, such as 3 feet 6 inches, is often sufficient and preferable to the 4 feet 8|inches gauge.

Tramways in towns, authorized by provisional order, are to be constructed in the middle of the road, and are not to be so laid that for 30 feet and upwards a less space than 9 feet 6 inches shall be left between the outside of the footpath and the rail, if, one-third of the owners or occupiers of premises abutting upon that part of the road object. Vehicles are thus enabled to stop at the road side without hindrance from the tramcars. To leave 9 feet 6 inches on each side of a single line of tramway of 4 feet 8 inches gauge a street must be upwards of 24 feet wide. No carriage used on a tramway must extend more than 11 inches beyond the outer edge of the wheels, and there must be a space of at least 15 inches between the sides of the widest carriages or engines to be used, when passing one another. A width of not less than 3 feet 2 inches between double lines and at passing places is thus necessary, and a double line of tramway, leaving 9 feet 6 inches space on each side, requires a street at least 32 feet 6 inches wide between the footways. In narrow roads there is a convenience in having the tramway at the side, and it is sometimes provided for in special Acts. The space between the rails, and for 18 inches beyond them, is repairable as part of the tramway. Power is given to local authorities to purchase tramways at the expiration of twenty-one years, and they may be removed under certain circumstances.

It appears from a parliamentary return that in 1886 there were 779 miles of street tramways open for traffic in Great Britain, on which a capital of 11,503,438 had been expended, the net receipts for the year being 563,735, and the working expenses 79 per cent, of the gross receipts.

Construction.The grooved rail first laid in England was 4^ inches wide and an inch thick, having a tread or rolling surface for the wheel If inches wide, and a groove f inch deep, f inch wide at the bottom, and 1^ inches wide at the top (fig. 3).

Fig. 3. The rail was spiked through to a longitudinal timber laid on cross sleepers, and secured to them by angle brackets and spikes. This rail and method of laying were gene rally adopted, but it was found that the heads of the spikes wore off, and the rails required respiking, and split and worked loose at the joints. A rail known as the box-rail was introduced, having flanges below on each side, through holes in which clips are driven to fasten the rail to the timber. This constitutes a good fastening, and the flanges give stiffness to the rail, but the clips cause gaps between the rail and the paving stones, which lead to the formation of ruts alongside the rails. The longitudinal timbers, instead of being laid on cross sleepers, on which the paving does not bed well, are often fixed in cast-iron chairs connected by transverse tie-bars. A bed of concrete is always laid under the longitudinal timbers, and should extend to the whole width of the paving. The rails first laid weighed 40 lb per yard, but it was soon found desirable to increase the weight to 60 Ib per yard. It is, however, impossible to fish the joints of rails like the above, and it was found that the working of the joints under the passage of the cars loosened the ends of the rails, dislocated the paving, and damaged both the tramway cars and ordinary vehicles. Tramways proved hardly able to withstand heavy street traffic; and to provide for steam traction a stronger form of rail and a better system of permanent way became necessary. Many forms of iron bearings have been devised, the rail being either supported continuously or on chairs at intervals. In the best of these the tram rail can be replaced when worn without disturbing the foundation. In the system used in Liverpool cast-iron longitudinal sleepers weighing 80 and 90 Ib a yard carry steel rails of a J section (fig. 4) weighing 40 lb a yard, both sleepers and rails being held down by bolts to jaws anchored in the concrete foundation. The rails can be renewed and the sleepers can be taken up with very little disturbance of the paving.

Fig. 4 Fig. 5

Steel rails of a flatfooted or a bridge section, and of such a depth as to constitute both rail and sleeper, are also used. In some of the latest and best examples the rail is of a flatfooted section (fig. 5), 6 or 7 inches deep, and 6 or 7 inches wide at the base, weighing 65 to 93 Ib per yard. The head has a groove either planed out or rolled in it, giving the usual profile to the upper surface. The joints are fished in the ordinary way, and are as strong as the rail itself. Cross ties are sometimes used, but when the rail is slightly bedded in the concrete foundation they are dispensed with. The paving is set in cement close against the rail, and is bedded directly or in sand on the base of the rail, upon which there is a bearing of 1^ or 2 inches. Such a tramway will stand steam traction and the heaviest street traffic, but the rail, which is of an expensive section, requires entire renewal when the head is worn out. Iron or steel continuous bearings are less elastic, and therefore more jarring and noisy than timber sleepers.

The profile of the upper surface of tram rails has been little altered since the first grooved rail was devised for Birkenhead in 1863, though slight modifications have been made in the form of the groove with the object of lessening tractive resistance. For the sake of the ordinary traffic the groove should not exceed 1 inch in width, and a rounded section with sides splaying outwards facilitates the forcing out of the mud and dirt. A nearly upright side next the tread or rolling surface with a splay on the inner side throws the mud away from the wheel. The upper corners of the rail should be angular, to make as thin a joint as possible between the rail and the paving. There has been a tendency to diminish the width, and a rail as narrow as 3 inches has been laid. A deviation from the usual profile has been adopted in Liverpool, where the groove is in the middle of a rail 31/4 inches wide.

Paving.A tramway must not only afford a good rolling surface capable of bearing the weights running on it, but it must also be able to resist the shocks of heavy vehicles crossing the rails in all directions. The space between the rails, and for 18 inches beyond them, which is repairable with the tramway, is always paved, sometimes in provincial towns and in the suburbs of London with wood, but generally with stone sets in the best manner on a concrete foundation. The sets alongside the rail should be carefully dressed and fitted to make a thin joint. There is much extra wear, and a tendency to form a rut alongside the rail, arising from ordinary wheels using the tram rail, and unless the surface of the paving is kept to the level of the rail the wheels of carriages are caught by the rail, and damage and accidents are caused. To resist the wear near the rails, chilled cast-iron blocks have been used where the traffic is great. On a macadamized road there is the same tendency to form a rut along the outer edge of the tramway paving, which is to some extent prevented by giving a serrated edge to the paving. There is always great difficulty in keeping the road surface to the level of the paving, and it is better to pave the entire width of a street in which a tramway is laid.

Curves.Although cars can be drawn round very sharp carves, the latter should be as easy as possible. A radius of 150 to 200 feet is the least that should be used when there is any choice, but necessity may compel the use of curves of 50 or even 30 feet radius. On such curves, however, the cars are liable to be strained, and the resistance to traction is greatly increased.

Passing places.A single line of tramway must have passing places for the cars, consisting of pieces of double line of length sufficient to hold two cars at least, with connecting curves and the necessary points and crossings. Where steam or other mechanical power is to be used the passing loops should be at least 200 feet in length. There is inevitable delay and interference with the street traffic at passing places, and where cars are to be run at frequent intervals it is better to lay down a double line if the street is wide enough. It is a great advantage to the ordinary traffic to have the cars moving always in the same direction on the same line of rails.

Points and crossings.For horse traction fixed points of chilled cast-iron or steel are sufficient, as the driver can turn his horses and direct the car on to either line of rails. When mechanical power is used, drop points or movable points are required. In the former the groove leading into the road to be taken is of the full depth, and the other groove shallow, so that the engine and cars naturally take the former. On coming out of the shallower groove to the deeper there is, how ever, a drop encountered which is damaging to the rolling stock, and especially to the engines. Movable points require setting by hand, or they are actuated by a spring or balance weight. In one form of spring point one groove is filled up by a tongue which is pressed down by wheels passing out of a loop, but which forms the side of the groove for wheels running the opposite direction. A spring point of steel, which is forced aside by the flange of the wheel passing out, and shuts close again by its own elasticity, is also successfully used. A movable point on one side of the way is sufficient. Crossings are either built up from rails cut to the required angle, or they are cast solid in steel or chilled iron. Filling pieces of the same material, roughened on the surface for foot hold, are inserted between the rails at the angles of points and crossings. Both points and crossings wear rapidly, and are trouble some to maintain in good condition, and when not so maintained are dangerous to ordinary traffic.

Cars.The tramcars generally in use in the United Kingdom are constructed to carry 22 persons inside and 24 outside. They are 16 feet long in the body, or 24 feet including the platforms at each end, and weigh 21/2 to 23/4 tons when empty and about 5 tons when fully loaded. Smaller cars to carry 20 or 14 persons inside, drawn by one horse, are useful to run at short intervals when the traffic is not great, a frequent service of cars being a great element of success. The car wheels are usually of steel or chilled iron, with a flange half an inch deep, and are fitted with powerful brakes. The axles are about 6 feet apart, giving a short wheel-base to enable the cars to pass sharp curves, but with the disadvantage of overhanging ends. Cars to be drawn by mechanical power, especially if outside passengers are to be carried, should have a flexible wheel-base, either by means of bogie frames or radiating axles. In Hamburg and Copenhagen tramcars have wheels without flanges, and a small guiding wheel running in the groove, which can be raised to allow the car to leave the track.

Traction.The tractive force required on a straight and level tramway is found to vary from 1/150 to 1/50 of the load, according to the condition of the rails. On a tramway in average condition it is about 1/100. The resistance is thus at the best nearly double that on a railway, and sometimes as much as on a good pavement. This is due to the friction of the flange of the wheel in the grooved rail, and to the circumstance that the latter is always more or less clogged with dirt. The clearance between the flange and the groove is necessarily small, as the former must have sufficient strength, and the latter must be narrow. The least inaccuracy of gauge, therefore, causes extra friction, which is greatly increased on curves. By removing the flanges from two of the four wheels of a tramway car Tresca found that the resistance was reduced from 1/100 to 1/148 of the load. The resistance due to gravity is of course not lessened on a tramway; and, if 1/100 of the load be the tractive force required on the level, twice as much, or 1/50 of the load, will be required on a gradient of 1 in 100 and three times as much on a gradient of 1 in 50. To start a tramcar, four or five times as great a pull is required as will keep it in motion afterwards, and the constant starting after stoppages, especially on inclines, is very destructive to horses. Horses employed on tramways are worked only a few hours a day, a day's work being a journey of 10 or 12 miles, or much less on steep gradients. In London a tramcar horse bought at the age of five years has to be sold at a low price after about four years work. On the Edinburgh tramways, in consequence of the steep gradients, the horses last a less time, and they have to be constantly shifted from steep to easier gradients. The cost of traction by horses is generally 6d. or 7d, per mile for two horses, and more when the gradients are steep.

Steam traction.The application of steam as a motive power on street tramways is attended with special difficulties, arising from the conditions under which the engines have to work. A tramway engine must be able to draw its load up steep gradients, demanding perhaps seven or eight times the power required on a level, and it must have the necessary adhesion without being too heavy for the permanent way. It must be capable of traversing sharp curves, of going backwards or forwards with safety, and of stopping and starting quickly. For the safety and convenience of the public the Board of Trade require that tramway engines shall have brakes to each wheel, to be applied by hand and by steam, a governor so arranged as to shut off the steam and apply the brakes when the engine exceeds the speed of 10 miles an hour or other stated speed, an indicator to show the speed, a whistle or bell to be sounded as a warning, and a fender to push aside obstructions; the engine must be free from noise produced by blast, and from clatter of machinery such as to constitute a reasonable ground of complaint; and the machinery and fire must be concealed from view; no smoke or steam must be emitted so as to constitute any reasonable ground of complaint to passengers or the public.

The first attempt to use steam on a modern tramway was with Grantham's combined engine and car. It was about 25 feet long, having a vertical boiler in a central compartment, with the steam cylinders below, driving one pair of wheels 2 feet 6 inches in diameter. It carried 20 passengers inside and 24 outside, weighing 6 tons empty and 12 tons when fully loaded. In a later car the boiler and machinery were at one end, and the body of the car was carried on a bogie frame. In a combined engine and car the weight of the car and passengers is utilized for adhesion of the driving wheels, and this is conveniently effected in Rowan's car, in which there are two four-wheel bogies, the leading one carrying the engine and boiler, and half the body of the car and passengers. The engine can be detached from the car for repair and another engine can be substituted in a few minutes. Economy of rolling stock, and the advantage of being able to use cars intended for horses, are in favour of independent engines. They are usually in general construction similar to locomotives, but are enclosed so as to resemble in outward appearance a short tramcar. The cylinders are 6 to 9 inches in diameter, with a stroke of 10 to 12 inches. The wheels are coupled, 2 to 3 feet in diameter, and the engines weigh 4 to 6 tons with fuel and water. The governor to shut off steam and apply the brakes when any determined speed is attained is actuated either by the engine wheels or by an independent wheel to prevent the possibility of the brakes being put on when the driving-wheels slip. An effectual way of rendering the exhaust steam invisible is to condense it by passing it through water in a tank, or through a shower of water let off at each blast, but when the water gets hot it must be changed, and in streets it is difficult to get rid of the hot water. Several methods of superheating by passing the exhaust steam through the fire have been adopted, but they are all attended with an increased consumption of fuel, which in cold damp weather is considerable. It is now preferred to pass the steam into tubes exposed to the air on the top of the engine car, from which the condensed water is returned to the feed-tank, to be again pumped into the boiler at a high temperature. Any steam remaining uncondensed passes into the smoke-box. Compound cylinders have been applied to tramway engines, giving a greater range of power, economizing fuel, and rendering the exhaust steam easier to deal with. The extra complication of a compound engine is, however, a drawback.

The cost of steam traction with engines of ordinary size is gene rally 3d. to 4d. per mile run by the engine, and more on lines with steep gradients. To this must be added for depreciation 10 per cent., or, according to some authorities, 15 percent. on the original cost of the engines, making altogether 4d. to 6d. per mile run on a tramway with average gradients.

Fireless engines. Fireless engines were first tried in New Orleans, and have been in successful use on tramways in France for some years. The motive power is obtained from water heated under pressure to a very high temperature in stationary boilers and carried in a reservoir, where it gives off steam as the pressure and temperature are reduced. Two tons of water heated to give a steam-pressure of 250 lb to the square inch serves for a run of 8 or 10 miles, leaving more than 9/10 of the water and a pressure of 20 to 25 ft above the atmosphere on returning to the boiler. Large boiler-power is required to reheat the engine reservoirs quickly, and this cannot be afforded for only a few engines, but, when worked on a sufficient scale, the fireless engines are claimed to be economical, the economy resulting from the generation of the steam in large stationary boilers.

Compressed air.Compressed air as a motive power offers the advantage of having neither steam nor the products of combustion to be got rid of. In Scott Moncrieffs engine, which was tried on the Vale of Clyde tramways in 1876, air was compressed to 310 ft on the square inch, and expanded in the cylinders from a uniform working pressure to that of the atmosphere. There is a considerable loss of heat during the expansion of the air which is attended with a serious loss of pressure, and in Mékarski's system, which has been in use for the propulsion of tramcars at Nantes for seven years, the loss of pressure is considerably lessened by heating the air during expansion. The air, at a pressure of 426 lb per square inch, is stored in cylindrical reservoirs beneath the car, and before use is passed through a vessel three quarters full of water heated to 300° F., by which it is heated and mixed with steam. The heat of the latter is absorbed by the air during its expansion, first to a working pressure which can be regulated by the driver, and then to atmospheric pressure in the cylinders. At Nantes the average cost for three years for propelling a car holding 34 persons was about 6d. per mile.

In San Francisco a main charged with air at a pressure of about 120 lb per square inch has been laid along the tram route, from which reservoirs on the cars are charged by means of standpipes and flexible connexions at convenient points, the operation taking a very short time. The inventor claims to utilize 30 per cent. of the power applied to the compressor.

Cable tramways.Street tramways worked by means of a wire rope have been in successful operation in San Francisco since 1873. There are now upwards of 24 miles of double line in San Francisco, and 10 miles in Chicago, and the system is being adopted in other American and colonial cities. It has also been in operation in England at Highgate Hill for several years, and is about to be adopted in other localities. The motive power is trans mitted from a stationary engine by a rope of steel wire running always in one direction up one track and down the other, in a tube midway between the rails, on pulleys which are arranged so as to suit curves and changes of gradient as well as straight and level lines. Over the rope is a slot 3/4 inch wide, in which travels a flat arm of steel connecting the dummy car with the gripper which grasps the cable. The flat arm is in three pieces, the two outer ones constituting a frame which carries the lower jaw of the gripper, with grooved rollers at each end of it, over which the cable runs when the gripper is not in action.

Fig. 6.-Gripper

The upper jaw is carried by the middle piece, which slides within the outer frame, and can be de pressed by a lever or screw, pressing the cable first on the rollers, and then on the lower jaw until it is firmly held. The speed of the cable, which is gene rally 6 to 8 miles an hour, is thus imparted to the car gradually and without jerk. The arrangements for passing the pulleys, for changing the dummy and cars from one line to the other at the end of the road, for keeping the cable uniformly taut, and for crossings and junctions with other lines are of considerable ingenuity. When the cars are cast off from the cable they must be stopped by hand brakes, which on steep gradients especially must be of great power.

Fig. 7.-Carrying pulley.

The system has advantages on double lines with few and easy curves when the gradients are long and steep, and it can be employed on gradients too steep for steam traction. On level lines it is doubtful if it could compete in economy with steam, or even with horse traction, unless with a very frequent service of cars, though then it presents the advantages of being comparatively quiet, and free from smoke and steam, and of admitting a frequent service of cars with little extra cost. On the cable roads of San Francisco it has been found that, of the average daily power employed, 68 per cent. is expended in moving the cables, &c., 28 per cent. for the cars, and 4 per cent. for passengers. It is considered that it is practicable to utilize in moving cars and passengers as much as 50 per cent. of the power, provided the cars are fully loaded and run at short intervals.

Electric motors.Electricity has been applied as a motive power on a tramway about 2 miles long at Blackpool. The current is conveyed by two copper conductors in a central channel beneath the roadway, and is communicated to the motors in the car by a collector running upon the conductors and passing through a narrow slit in the channel. The return current passes through the rails. The cars carry as many as 56 passengers on a level line. Tramways have also been worked by accumulators at Antwerp and Brussels, but the weight of them appears to be at present prohibitory to this method of applying electricity, except for short trips. See Traction.

For fuller information, see D. K. Clark, Tramways, their Construction and Maintenance; F. Sérafon, Les Tramways et les Chemins de Per sur Routes; "Street Tramways," Proc. Inst. C. E., vol. l.-vol. Ixvii.; "The Working of Tramways by Steam," Ibid., vol. Ixxix.; and F. B. Smith, Cable Tramways. (T. C.)