Switches

[Amtrak Watcher]

While riding along on various trips, I often wonder (with a little worry) about switches in the tracks. A derailment could be the result of an error.

Who moves the switches? Does the engineer move them by radio, does he ask someone else to move them, or does everyone trust “the system” to have everything in the right positions at the right times?

How does the engineer know a switch is in the correct position? Are there lights or something?

Can the engineer get an indication of a mis-positioned switch in enough time to stop the train?

 

[AlanB]

Amtrak Watcher,

Wow, so many very good questions. Where to start first? :unsure:

Most mainline switches today are controlled remotely from a central dispatch office for the RR that owns the tracks. Years ago each group of switches had it’s own local switch tower, where the person manning the tower was responsible for moving the switches. There are still some towers at very busy, complex junctions; which are still in operation. This is particularly true around Chicago, where just about every major RR meets.

However, once you get off of the mainlines most switches are manual. This means that the conductor must stand on the ground next to the switch and move it by means of a lever alongside the tracks.

Now the engineer is really just trusting that the system is working properly. The engineer is indeed told via signal lights, that his train is going to switch tracks. However, he usually can’t see the switch far enough ahead to know if it is properly aligned. If the train is traveling very slowly on straight track, then he might be able to stop if he saw a problem, but if he’s going 30 or 40 MPH he probably won’t be able to stop in time. Also if the switch is around a curve, then it’s out of sight until it’s too late for the engineer to react.

On the other hand, switches operate on what is called an interlock system. What this means is that when a dispatcher moves a switch, the system checks to make sure that there is no conflicts. In other words if the train is moving from track #1 to track #2, then both the switch on track #1 must be positioned properly, as well as the corresponding switch on track #2. If the switch on track #2 doesn’t move, then the engineer will receive a stop signal long before he gets to the first switch.

It’s not until all switches have moved to the proper position, and there are no conflicting switches in the area, that the dispatcher can give the train a signal to proceed. In fact the dispatcher doesn’t even really control that last signal before the interlock. He can make the signal go to stop, but he can’t make it go back to proceed. The interlock automatically sets the signal, once all switch movements have been properly completed. If a switch jams or if the track that your train was going to switch to has another train in the way, then the signal before the switch will remain at “Danger”. That’s the RR term for stop.

The interlock system also prevents the dispatcher from trying to move a switch that a train is currently crossing or just about to cross. Until the train moves out of the block (a section of track controlled by two signals) that the switch is in, he can’t move the switch to a new position.

While it doesn’t happen often, occasionally the interlock system can fail. In that case, by the time the engineer realizes that the switch is wrong or not fully aligned; it is too late to stop. Fortunately this type of failure is very rare in the industry. It does happen more frequently with the manual switches.

 

[battalion51]

I think Alan did a pretty good job on that one, but there are a few additional things I want to address. There are some "main lines" that do not have Centralized Traffic Control (which is where the Dispatcher controls all movements, lines switches, etc.). But there is a second type of Control system that is common place throughout the U.S., that being Form D Control System. Form D is a system where a dispatcher gives a train permission to occupy a section of track (otherwise known as a block). When two trains are to meet a siding is designated by the dispatcher, the train going in siding is responsible for lining the switch in for their movement, and relining it for the other train to pass. Upon their exit at the other end they are responsible for lining the switch to exit the siding, and restoring the switch to the normal position. Form D is a rather prehistoric way of running a railroad, but it relies on the employees to make sure all switches are lined properly when they have finished their work.