Changes in Locomotive Maintenance Practices
Steam traction involved the procurement of many extra locomotives because of the large amount of cleaning, lubrication, descaling and minor repairs that were necessary.
This resulted in all engines spending a considerable proportion of their life in the shops or sheds instead of out on the railway pulling trains. Additionally there was a lot of time spent in firing and other preparation before eachday's working.
It was these considerations, amongst others, that led in the UK and many other countries to the demise of steam and the gradual introduction of diesel and electrical power since the SecondWorldWar. Diesel and electrical power has also enabled designers to dispense with large driving wheels and to introduce power driven bogies.
Also in recent years both locomotives and multiple units have been designed with motive power packages and self contained units that can be removed or replaced for maintenance. This has the effect of reducing yet further the amount of time that trains or locomotives have to be out of service.
'Carriages'to the Modern Carbodies
Third class passengers were often carried in simple wagons very little different from ?cattle trucks'. Sometimes as bodies were mounted on one truck with the seats ?facing or ba towards the engine. The doors on these early coaches were on each side, one per coach compartment, with no connection between the compartments. The carriages on suburban stopping trains on BR retained an element of the same layout with individual unconnected compartments and single ?slam' side doors for well over a hundred ye and distances increased, this quickly evolve introduction of a side corridor, to the basic carriage layout which remained
normalfor main line railways.
Early American railways, however, adopted the open coach with passengers sitting each side of an open corridor, boarding and alighting from the train through doors at the ends. Many of the world's rail adopted the open plan for both main line and suburban services with doors at carriage ends and walk-through connection down the full length of the train.
Most metros and light rail systems have open plan layouts in the cars.
In this case however boarding times are critical and doors only at car ends would be too restrictive. In this case there is a very fine balance between the number of doors and the number of seats provided.
The levels and curvature of platforms also has an effect on the design of cars and this varies considerably around the world. Increasing consideration is being given to the need to accommodate disabled passengers, especially those in wheelchairs.
Since the earliest days of railways, carbody structures have evolved and become considerably stronger, lighter and more economic. As mentioned previously, the earliest carriages were largely of wooden construction. These proved to have a very low crash resistance when accidents occurred with a high rate of injury and loss of life.
As early as 1840, in the UK the Railway Inspectorate was set up to inspect newly constructed railways and to certify fitness for public travel. Various accidents investigated by the Inspectorate over the years have led to progressively higher standards being set for the design of rolling stock. The first stage was to introduce a wrought iron and later steel underframe which fully supported the wooden superstructure. This system lasted well and was still being used in new stock up to the 195 was that all the strength was in the chassis which performed well in collisions but body work splintered, still causing much loss of life and physical injury.
The next stage was the use of a steel underframe with steel or aluminium framing to the superstructure. This performed much better in crashes but the whole design was getting very heavy and expensive.
Moderncars and coaches are designed on the In this case the whole structure is designed as a single monolithic unit, spanning between the main bogie supports. The structure then takes all the bending, shear and torsion stresses as an entity.
The final form is usually a composite of aluminium extrusions and welded stainless steel with a ?stressed skin'. All loa between the various components. The resulting design is considerably lighter than the previous design and is much akin to aircraft structural design. The lighter design coupled with higher stresses and repeated loading means that fatigue considerations become increasingly important. Summarising, these developments of carbody design over the last almost two centuries are characterised by:
These rolling stock characteristics lead to:
•Lower energy consumption
•Higher passenger comfort
•Higher passenger/carbody mass ratio
Main Line Train Performance Issues
When considering the engineering of a railway from the rolling stock point of view, train performance demands and issues need to be fully considered. These vary according to location and whether or not it is Main line, Metro or Light Rail.
The performance issues on Main Line railways for consideration are as follows:
•Is the traffic mainly one type (e.g. high speed express passenger) or mixed speed and type?
•What will be the impact on the long distance passenger carrying capacity of the railway of slow freight and stopping trains?
•What capacity will the signalling allow? (This will depend largely on such factors as the length of the signalling sections and whether there is uni-directional or bi-directional signalling.)
•Are there many passing loops or ?slow line' importance, to allow expresses to pass?
•What acceleration, braking characteristics and tractive effort is required to ensure that trains can work to desirable timetables?
•What are the maximum gradients on the line? (These will effect the previous consideration greatly.)
•How many speed restrictions are likely and what recovery will be required of time lost?