What measures do railway cars use to avoid collision?

Question

I have often wondered how 2 trains avoid traveling on the same rail avoid colliding with each other. How do the appraoching trains, accidentally traveling on the same rail avoid this collision? With the frequent use of the railroad, why aren't there a higher occurence rate of collision?

Answer 1

In the US, there are many different ways, primary of which is a universally applied code of operating rules, referenced here often as the GCOR.

One method employed is the use of automatic “block signals,” that will indicate track occupancy or other conditions that may threaten a collision.  The most widely used method of operation is “CTC,” or Centralized Traffic Control.  This allows multiple trains operating in opposing direction over a single track.  The train dispatcher has control over some signals, as well as the switches that are used in conjunction with these signals, to line (shunt) a train into a siding for an opposing movement to pass, or to let a following train with a higher maximum authorized speed to run around.

A similar method of operation, still with the use of controlled signals and automatic block signals, is called an “interlocking.”  These may be automatic, but more often they too are controlled by a person called an “Interlocking Operator,” as opposed to the train dispatcher in CTC.

In territories where there are only automatic block signals, or “dark territory” where there are no signals at all, trains are usually operated by methods known as DTC (Direct Traffic Control) or TWC (Track Warrant Control), wherein the operators of trains receive their operating instructions via radio, as a rule, directly from the dispatcher, such as when and where to stop or take a siding.

In the old days, these train movements were controlled by “train orders” issued to the crews when departing their initial terminal, with orders being either superceded or annulled by additional train orders received from an open train order office on line.  You may have seen images of trainmen or enginemen leaning out their windows scooping the orders of an “order post,” or being “hooped up” by a train order operator holding a train order hoop.

During this area, there was also a method called a "staff system" where a train would carry an actual "staff," a stick, basically, and when clearing the main track at the opposit end of the territory, would physically pass the staff to an opposing train, which would use it to travel to the other end of the staff system limits, then hand it off to that train, and so on.  This ensure only one train at a time was out on the track.

There was another system, called ABR (Absolute Block Register).  These wre common on brach lines, where a train would "log onto" the main by entering information on a register.  A train needing to enter the area had to check the register before doing so.  If the other train had not registered out of the territory, the other train had to wait until they did so before entering these limits.  The staff system and ABR systems were almost exlusively used on branch lines in dark territory.

There are sections of “double track,” where there are two tracks, where traffic is authorized to operate in one direction on one track, and in the opposite direction on the other, referred to as “current of traffic.”  But, don’t be fooled if two tracks are side by side.  These may not be operating as “double track,” but may in fact be multiple main track or within interlocking limits, which in both cases trains can operate under signal indication on either track in either direction.  There is a current RailTail on my 360 blog titled “The Thermos” that demonstrates what can happen when a pedestrian is walking along the tracks in multiple main track interlocking limits.

Answer 2

Trains avoid collision at a couple of different levels.

First, there is a signal system that senses where trains are and displays a signal, either directly to the cab of an approaching train, or to trackside signal lights similar to the traffic lights you see when you drive.  The signal system, whichever one is in use - there are several - directs a train to slow or stop when it gets too close to another train.  Some older tracks are set up in such a way that travel in only one direction is allowed without special permission.

Second, the trains are dispatched, usually from a central location, so that trains can't be sent down the same section of track towards one another.

Third, should the signal system or the dispatcher fail, the Engineer and sometimes a conductor will hopefully see an oncoming train on the same track and stop in time.

Answer 3

Because they don't hit each other........

Answer 4

"Timing is everything," especially with railroads.  Trains are timed with signals to avoid collisions.  The signals can either slow or stop a train, depending on conditions.

Also, departure times can be staggered so that every train can have several hundred miles between them.  This is especially important when passenger and freight service share the same tracks.

Some subway trains, the kind that run underground cities, have an added safety measure.  In New York City, next to every traffic signal is a tripping lever, which raises up when the signal is red.  If a operator breaks the red, the tripping lever will come in contact with the braking lever on the wheels of the subway car.  This will lock the brakes against the wheels, and bring the car to a stop as fast as conditions allow.

Answer 5

they use a timetable  and  D.T.C. block orders .if you stay in the U.S / that's how we got time zones from the railroads.

Answer 6

Think about it... When you drive down a road and you cross another road, what keeps another driver doing exactly the same thing from hitting you at high speed?  You probably cross 200 intersections a day!  You should get in easily a dozen accidents every day.  Why don't you?

You'll say, well, there are rules and gadgets to help.   Rules about stopping and looking; and mechanical signal systems like traffic lights.

It's the same on the railroad, except with a few differences.

First, on the railroad there's a person whose job it is to "control" all train movements.  Sometimes he controls trains by having published a timetable they must follow; sometimes he controls them by verbal/written order; and sometimes by remotely controlling the mechanical signals.

Another thing about trains is ... they follow a track.  You'll know where they'll be.  That makes it easy to automatically detect the presence of a train, which allows mechanical signals to be much more sophisticated.   It's even possible to have the mechanical signal show up on a display in the locomotive cab, and then if the engineer ignores a restrictive signal, to forcibly override and stop the train.  You see this in the more dense passenger lines, and on a few freight lines (the Santa Fe from Chicago to L.A.)  

I won't talk about how signals work because of security concerns.  But it's not hard to find out if you're interested.

And of course, trains have two people in the cab usually.  One driver can miss a signal; harder for two people to both miss a signal.

Answer 7

Please invite me to wonder with you.

Answer 8

"Every railroad accident involves the violation of at least two operating rules. at least one of which is violated habitually."

I don't remember where I read that, but every railroader I met agrees.