Switches and crossings

(Lawrence) My name is Lawrence Wilton, and I’m a graduate engineer working for Network Rail. I’m here today to teach you about switches and crossings. The simplest form of S and C is the turn out. This is a left-hand turn-out. As you can see, it diverges from the main route in a leftward direction. This is how it works. In normal mode, the left hand wheel rolls along the switch rail and there’s flange way clearance for the right wheel to continue along the stock rail. The inside surface of the right flange is kept on course by the track rail. This restrains the wheel set and ensures it’ is directed along the correct route. Meanwhile, the left wheel transfers contact between the different parts of the crossing. That’s where there’s a high impact load. In the reverse the right wheel rolls over the switch rail and follows its geometry. The inside surface of the left flange is guided by the check, forcing it to follow the stock rail on the new route and the right hand wheel makes a crossing, again, impacting a load on the crossing nose.

(Narrator) There are many different types of switch and crossing on the network. They include turn-outs, diamonds, cross-overs, and slip-diamonds. The type we use is determined by a number of factors including the number of lines involved, frequency of use and running line speed. Trains travelling at high speeds need long switches and crossings. At low speed, such as in stations, trains can make tighter turns. Train movement across the network are set and controlled by signalers who use switches to set routes for trains.

Switches can be propelled by various devices. One of the simplest forms is a ground frame set-up. A series of rods and cams attached to levers in signal boxes. These are now being largely replaced by remotely operated hydraulic and electro-mechanical devices.

(Lawrence) Seen by rail-sides all across the country, this is an HW2000 points machine. This is electro-mechanical. What we have here is your drive motor. To check that motor has done its job, over here we have an interlocking and detection system. Detection tells us when the points have completed their travel and locked. Locking holds the points in this state, so they cannot be physically moved. So when a train runs over the top, it remains in position. Facing point locks are one of the most important safety features on the S and C layout. They ensure that the points cannot be moved when set. This is important because failure to lock the switches could cause a derailment.

(Narrator) As engineers, we face an ongoing challenge to maintain and improve our switch and crossing assets. Trains can create large impact and lateral forces as they change course. And these forces can cause wear and deformation. Switches and crossings therefore have a limited lifespan before we need to replace them. Less than 5% of track miles are made up of switches and crossings but over 17% of our maintenance budget is spent on them. We’ll continue to research and develop new inspection techniques and material usage to increase their performance.

(Lawrence) It’s all about creating a network that’s safe, reliable and efficient. It’s what we do.

Unit 6