Design of Railway Track or P-way is another very exciting and demanding domain for newbie Civil Engineers to explore career opportunities. If you want to know some basics of Railway Track Design, please read this blog for details.
Opportunities in the Railway Industry?
Railway or P-way Industry involves design, construction, operation & maintenance of Light Rail or Heavy Rail to ensure safe & effective transportation of people & goods.
To know more about types of Railways, please read this blog:
Elements of Railway Track Design:
- Horizontal Alignment Design
- Vertical Alignment Design
- Superelevation Unbalance
Horizontal Alignment Design
The horizontal alignment of the railway track or P-way consists of a series of Circular Curves, connected by Straight Lines. In the case of low-speed tracks, straight sections are connected with curve sections without providing transition.
However, incase high-speed tracks, straight sections are connected to the curve sections with the help transition lengths and superelevation.
Circular curves are provided to provide a smooth change in direction of travel. A Constant centripetal force is applied from train wheels, which can be offset by CANT (super-elevation), to assist the change in the direction of travel.
Why Transition is provided?
Transition curves are used, to avoid an instant change of radius, which would be very perceptible at high speed, inside the train. For highspeed track, when the alignment moves from straight section to curve section, it is essential that this change in direction takes place smoothly. So, transition curves are used.
Transition curve comes with an infinite radius value at one end (where it ties with straight section) and specified curve value (where it ties with curve section). As a result, a gradual shift takes place within the full length of the transition curve.
Why Superelevation is provided?
To counteract, the effect of the lateral acceleration, and the resulting centrifugal force, the outside rail of a curve, is raised by a distance above the inside rail, represents by ‘e’ here. where ‘e’ is called superelevation.
Vertical Alignment Design
Vertical alignment of Railway track or P-way is a combination of constant vertical grades and vertical curves.
Vertical gradients of Railway Track are controlled by vehicle braking and traction power. Vertical Curves are used to change the grades of the railway track to minimise the Cut / Fill and provide a desirable longitudinal gradient for the sustainable drainage system. There are two key parameters, of vertical curves.
- Curve Length
- Curve Radius
Curve Length plays a very significant role for a compliant high-speed railway track. Vertical curves are defined by parabolas having a constant rate of change in grade. The Railway Track should be designed with longer vertical curves whenever feasible. Both sag and crest vertical curves should have the maximum probable length, specifically if approach and departure tangents are long.
When Railway Tracks are placed, it is recommended to provide a fixed value of superelevation. But sometime Railway Tracks run with different speeds, for various reasons. As a result, the variance in superelevation requirement for lower or greater speed is called Superelevation Unbalance.
How to define Railway Track Speed at Curves?
Design Speed of Railway Track at curve is dependent on the following four factors:
- Safe Speed
- Overturning Speed
- Signal Speed
- Maximum Authorized Speed
The speed limit above which, the Railway or P-way becomes unbalanced, and in a great risk of derailment, is considered as Safe Speed.
The speed at which the Railway or P-way will overturn or derail because centrifugal force overrides the gravity is called Overturning Speed.
The speed for which, the signal speed control system is designed, is called Signal Speed. Ideally, signal speed should be designed, at which the signal operator would normally operate the Railway or P-way, without needless use of Overspeed braking system.
Maximum Authorised Speed:
The speed at which the Railway Track shall be designed, applying maximum acceptable definite superelevation, and superelevation unbalance, is called Maximum Authorized Speed.
The primary objective of Railway Track or P-way design is to provide an efficient, economical, eco-friendly and comfortable transportation system with adequate health and safety measures in place.
The design guidelines vary from country to country, but it is very important for designers and engineers to learn the best design and construction practices to improve the efficiency of the Railway or P-way Transportation System.
I hope this blog gives you a brief knowledge of Railway or P-way Track design Process. Please feel free to like, share and comment.
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