Transportation: Emerging Realities Les Transports
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CTRF Transportation: Emerging Realities Les Transports: realites en puissance• VOLUME 2 ess-nrch rurn rh 1:2./Jd -*/ Y p1j iu Actes J 21 er1iJ confer si 111111 Torconit),JJ1IJfiJ 25 cats Inf./I, I 717l7 418 WHAT IF? / WHY NOT? A Railway Tridea F.H.Howard P Eng Richmond B C 1. RUBBER AND RAIL The ability of a locomotive to exert tractive effort or drawbar pull - the measure of what it could lift vertically, say over the edge of a cliff - and so, once the train's resistance has been determined, what tonnage of train it can start, is restricted by its wheen adhesion to the rails, normally about /14 of its weight. wheel slip control (replacing sanding) has now raised this to about 1/3. Too much power, and its wheels will slip. Starting a train is adhesion-limited; running it is horsepower-limited. When inverted, this fraction becomes "Factor of Adhesion" and refers to steel wheels gripping - or slipping - on steel rails. Some locomotives are ballasted to achieve adhesion, which affects braking too.. Heavier trailing tonnages can be moved if a much lower Factor of Adhesion can be developed. Such a low factor is indeed developed by rubber on paving. Assuming the road is dry and the tires sound, a rubber-tired highway tractor can lift half its own weight, with the corresponding capacity to pull a heavy trailing load, usually a semi-trailer, also on rubber tires. 1 Howard 419 A number of rail vehicles use a Hi-Rail device,. hydraulically-lowered sets of rail wheels, commonly attached to rubber-tired track inspection and maintenance equipment, especially automobiles, pickup trucks or vans; sometimes little cranes. This makes them amphibious, so to speak, at home on road and rail. When finished with rail duties, they can get off the track and go away. This feature has been used in a most sophisticated way in Saskatchewan. Originally conceived by the Highways Department as a solution to the projected abandonment of some railway branches and consequent overloading of thinly-paved roads, the Brandt Road Rail unit is a unique heavy-duty bi-medium quasi-locomotive. Using this basic Hi-Rail principle to guide it while in the rail mode, it weighs up to 25 tons (depending on auxiliary attachments) of which 14 tons rest on the driving wheels, and exerts 30,000 lbs of drawbar pull to start and 425 HP to run. This ingenious machine depends for traction on its tires adhering to steel rails at a Factor of 2, clearly superior to steel on steel, and can pull its own steel-borne weight. The original purchaser uses it to alternate between two isolated short railway lines. Another promising employment is in areas where unconnected branches need irregular service; a single power unit can visit them on different days. At about $500,000, it costs considerably less than a new diesel switcher. 2 Howard 420 Fig I shows this versatile creation et, This paper proposes the further development of that marriage of steel on rubber. Instead of adding Hi-Rail flexibility to the truck/locomotive, let it remain solely rubber-tired, but pave the railway. Not pave over the tracks, but up to each side, and let the trailing train'§ steel wheels remain on steel rails as always, with their low rolling resistance*. The towing truck to do what it does best, provide high rubber-on-asphalt adhesion (but no longer pulling a high-resistance trailer). The paving need be to no particular degree of smoothness and can extend the length of a branch or just a siding, wherever this low-cost system can be exploited. In fact an entire small freight yard could be paved right across, and say a heavy- duty ballasted 4x4 truck be substituted for a diesel switcher at half the capital cost. It could then dart around the yard from track to track without shunting in out, back and forth, through rail-bound switches. Automatic transmission is mandatory to protect clutches against their destruction *Train resistance is an arcane science, involving a complex calculation known as the Davis Formula. While starting resistance is an indistinct number, rolling resistance, varying with speed and inversely with weight per axle, comes out at about 5 lbs per ton at medium speed 3 Howard 421 Care must be taken to prevent the train exercising its resistance by trying to overturn the pulling vehicle, as farm implements used to overturn tractors by coupling them too high. The standard railroad coupler height is 34/12", and no drawbar should be mounted lower. Now a mythical 17-ton 4x4 truck on steel wheels could exert 8,000 lbs drawbar pull. The same truck, its rubber tires rolling on asphalt, can exert 17,000 lbs, about as much as a young locomotive. The Brandt truck-motive develops 30,000 lbs, more than many small steam locomotives of 65 tons used to. It has hauled 2,000 tons with its wheels adhering to rails. When they are on paving, with the train still on rails, what tonnage can be started? Let us speculate: 5,000 tons? Any road vehicle converted to rail operation must have standard air brakes, which Brandt has, and the . authorities will almost certainly ordain headlight, ditch lights, a horn and bell. The rear view must be of the best; Brandt uses a TV monitor. Caterpillar offers a variation on this theme: a massive 4x4 log skidder with big wheels, suitably modified by replacing the logging and bulldozing apparatus with couplers, air compressor, reservoir and controls. The model examined generates a starting drawbar pull of 44,000 lbs, which, in common with all constant-horsepower locomotives, declines with speed in a hyperbolic curve. 4 Howard 422 This is shown in Fig 2 • ; Horsepower in this case is markedly lower than Brandt's which will affect its top speed. The factory weight is about 16 tons, and in pursuit of effective traction, ballast is needed, along with the fattest of bald tires. Its drawbar pull of 10,000 lbs at 6 mph should move along a 10,000 ton. train. It will be priced at about $450,000+. A one-man engine crew can work the yard, and for the road, negotiations will determine its size. In this regard, a Short Line may be able to economize on engine manning. 5 Howard 423 2. TRACKS UP - MAINTENANCE DOWN This is the revival of an old idea and there may not be many more lines of railway laid, since the industry is mature and if anything is diminishing in size if not in all species of traffic. Short Lining is not going to reverse this trend. But when a new railroad is to be built, such as for a High Speed Train, or an existing line relocated or massively improved, or a heavily-damaged or washed-out line repaired, this paper explores the practicability and poses the alternative of the trackage no longer laid on the ground but on an elevated structure instead. It is acknowledged without argument or reservation that the greatest obstacle to lowest-cost railroad operation is gradient. To quote the late John Barriger,"....whenever a train ascends 8 feet, irrespective of the rate of grade, the locomotive does as much work in overcoming the force of gravity as is performed in hauling the train one mile on level tangent track.* An elevated structure can provide an exactly level track by varying the heights of its supports. An elevated main line railway, not to be confused with the New York or Chicago elevated transit lines, eliminates the grading, ballast and ties required with conventional trackwork, replacing them with a level structure of rails fastened to a concrete slab. Such a form of construction eliminates the maintenance consisting of repetitive ballast cleaning, tie replacement, the constant ditching for the critical drainage and the every-spring recovery from frost, to say nothing of the burden of highway grade crossings and keeping culverts clear. * John W Barriger, "Super Railroads" Simmons-Boardman 1955 6 Howard 424 In short, along with grade crossings and blocked culverts, these are all the impedimenta of railroad Maintenance of Way Departments, reporting to the Civil Engineers. This profession also designs bridges, and this proposal is for a continuous bridge. The Skytrain system of British Columbia Rapid Transit Inc provides a modern example of cross-country elevated railroad construction. Although moving small trains of very light weight at medium speed. the design can be upgraded so as to accomodate long trains of very heavy tonnage or short trains at higher speeds. This railway was built for Expo 86 as an example of future technology in tune with a World Exposition. Originally joining two areas of the Fair, there are now about 17 km. of elevated high-density operation, with plans for more - when funds are available. Double trackways are supported on poured-in-place reinforced concrete T columns. They consist of pre-stressed post-tensioned concrete slabs about 100'long, with rails fastened to the concrete with conventional fasteners. The slabs are drained, and in this case incorporate low coamings along each side for protection against derailments. Such a concept forms one basis for main line railroad construction, although there could be others, one of which is a steel structure with heavy bridge-type spans on steel columns. Steel's advantage is its superior weight-strength ratio. Weathering steel at higher cost will eliminate frequent painting; concrete of course is practically weatherproof. Steel bridges would be of the deck girder configuration for better snow-clearing. Wooden trestles can also produce a level elevated line without ballast, but with significant maintenance and with labour-intensive erection.