How do trains change tracks?

With just a slight movement of the rail track, the train can change its trajectory. This clever track switching design is achieved with a simple trick on the wheel and track. In this article I am going to explain how it works!

Basic concept behind railway track switching

To understand the concept first, you can see this simple case as shown in fig 1. Let’s focus on a track.

Now, assume there is one branch diversion for that track. Will the wheel roll through the left or right track?

Fig 1 : The wheel roll through left or right track

Why do train wheels have a flange?

The wheel’s journey is unpredictable! but as we see in the figure, the wheel rolls through the right track. Because wheels used on the rails have a flange (refer fig 2a) on one side. The flange is a safety feature of the wheel that ensures the wheel never leaves the track as shown fig 2b.

Fig 2a : Wheel roll through the right track
Fig 2b : The flange is a safety feature of the wheel

Due to the presence of the flange, it is impossible for the wheel to travel through the left track. If you want to make the wheel roll through the left track, just make the right track a separate piece and bend it before the wheel reaches that point. This is the fundamental concept behind track switching(refer fig 3).

Fig 3 : Bend the right track to roll the wheel through the left track

Tongue track

Now, let's see how this works when both pairs of the tracks are present. The flange is always on the inner side of the wheels. The portion of the track that is able to bend is called a tongue track (refer fig 4). When the tongue tracks are bent as shown in fig 4, the train will move on the yellow track. Remember, due to the presence of the flange the left wheel cannot roll on the light blue track. Due to the same bending, the dark blue tongue is not at all touching the track, a large gap can be observed. So, the right wheel will also be able to follow the yellow track on that side without any trouble.

Fig 4 : Tongue track

Now let's see what will happen if I bend the tongue tracks in the opposite way. This time, a gap is created at the orange tongue region (refer fig 5). In turn, the train will easily adopt the blue track and move straight on the right track. What a simple and effective mechanism!

Fig 5 : Due to gap at orange tongue region, the wheel roll on light blue track

Rail crossover and why they are used?

Using the mechanism I have explained above, the train switches tracks perfectly. However, if you run your train on these tracks, it will inevitably derail! The issue is the crossing. The tongue tracks cross at a point. If the crossing design is as shown in fig 4, the train is going to hit the orange tongue and derail as shown in fig 6.

Fig 6 : Illustration of crossing issue

Let’s see how to overcome this issue. To solve this issue, provide some gaps in the crossing junction (refer fig 7).

Fig 7 : Gap between crossing areas

In this new crossing design, whether the train is going through the left or right track the wheels cross the junction without hitting any track. However, just observe the rail wheel at the crossing point. You can see that the wheels drop down in this gap(refer fig 8). This can cause you discomfort while travelling.

Fig 8 : Wheels drop down in the gap

Can you suggest a solution for this issue? We can overcome this issue just by increasing the length of the tongue rails as shown in fig 9a. They will provide good support to wheels during the movement over the rail gaps(refer fig 9b).

Fig 9a : Increase the length of tongue rail
Fig 9b : By increasing length of tongue rail provide good support to wheels

Did you know, the length of the moving part of the tongue tracks need not to be so lengthy. You can reduce the length of the tongues by pivoting them as shown in fig 10.

Fig 10 : Use pivot point to reduce the length of the tongue

That's it for today! I hope you understand and enjoy this explanation of rail track switching. In the next article we will go in depth about check rails, why is it needed? How do we operate the rail switch?

Thank you for reading!


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.