How does a train switch tracks?

In our previous article we have learned about the fundamental concept of rail switch. Now in this article I am going to explain the advanced concepts such as : Operating mechanism of the switches, designing of switching tracks efficiently and how the radius of turning of the train affects the usage of guard rails? So, let’s begin.

Guard rails in rail track switching

As I have shown in fig 1, there are two additional pieces placed in the rail track near the crossing. These are nothing but guard rails or we also call them check rails. They have an important duty during the crossing.

Fig 1 : Guard rails

Let’s discuss what would happen if they were not present. The low radius track has a high angle of deviation and vice versa as I have shown in fig 2a. But majority of the tracks use a larger radius for the turn, for smooth running of trains at high speed. Here is the issue that arises for a high radius or low angle deviation track.

Fig 2a : High and low radius track
Fig 2b : Low angle deviation track

There is a high possibility for the wheel to travel on the wing rail and the wheel will derail as I have shown in fig 3.

Fig 3 : Wheel is derail due to high radius or low angle deviation track

The check rails are placed with a fixed gap with the main rails, on either side. Even if the wheel tries to travel on the wing rail, the check rail channels the wheels to prevent this as I have shown in fig 4a. And the wheels will easily pass through the intended trajectory as you can see in fig 4b.

Fig 4a : Check rail channelize the wheels
Fig 4b: Wheels will pass through the intended path

Design optimization of switching tracks

Can you predict the maximum stress points in these switching rails? It is at the toe of the rail switch and the nose of the crossing, as I have shown below in fig 5. The red colour area shows the stress points. These components have to be often replaced due to wear and tear compared to the main rails. This is why the tongue rail is divided into two parts: bendable tongue track and fixed tongue track as I have pointed out in fig 6.

Fig 5 : Stress points in the switching rails
Fig 6 : Fixed and bendable tongue track

When the switch is at the end of its life, just replace the bendable switch rail. By doing so, we can reduce the quantity of iron that needs to be replaced after it's worn out.

Who controls the rail track switch?

The tongue tracks are operated using a switching rod. Earlier this switching rod was controlled manually. The man who operated the switching rod was called a point man (refer fig 7). Nowadays electric motors control switching rods. It does this task upon receiving instruction from an operator. As I have shown in fig 7b, operators operate the electric motors from the control room we call it a point machine.

Fig 7 : Pointman operate switching rod
Fig 8 : Point machine

It's all about railtrack switching. I hope you understand all the concepts regarding the check rails. I hope you liked both article 1 and article 2.


Yogeshwari S Gaddam

Yogeshwari S Gaddam, B.E in electrical engineering, currently she is working at Lesics Engineers Pvt. Ltd. as a manager. Each day she encounters new challenges and loves the complexity that each project requires. Yogeshwari has done projects such as Tesla model-3's motor(IPM-SynRM), RMF, SynRM motors, Etc. To know more about the author check this link.