What do the lights that trains go under mean?

Question

Some roads around town run parallel to train tracks and you can see big metal bars that the trains go under and they have lights on them. It almost looks like traffic lights for trains. Is that what they are? Sometimes they are red, I think sometimes green, not sure. I was just wondering because it would be interesting to look at those and know if a train is coming and how far away it is.

Answer 1

These lights are signals. The color may be red, yellow, green or lunar (this is a bluish-white light). They are referred to as "fixed" signals. The "aspect" of the signal conveys information to the approaching train. When mounted on the "bars" overhead, this is called a signal bridge. When next to the rail, they are signal "masts". In addition, shorter ones are referred to as "pot" signals or dwarf signals. (And no, this is not the 'pot' you're thinking about).

Red means stop, flashing yellow means proceed prepared to pass the next signal not exceeding 40 MPH, yellow means slow down (not exceeding 40 MPH) and be prepared to stop short of the next signal and green means all clear. As an example, the color may be green but the aspect is "clear".

In addition. signals controlling movement for main track or "diverging" route are stacked. For example, if a signal has two signal "heads", the signal may have the top unit red, with the bottom unit green. This means that the train is going to go on the diverging route with a clear aspect (bottom green) and not proceed on the main track (top red).

There are many different combinations. Red over yellow, double yellow, flashing yellow, red over lunar, red over red over green, and so on. Signal masts may also display flashing red and other combinations, each aspect of each signal conveys different information about route to be used OR track occupancy.

In addition, these signals are seperated into sub-groups; ABS (automatic block signal), Absolute Signals (found within CTC or Interlocking limits) Distant Signals, Grade Signals and Controlled Signals.

The main difference between them is what is necessary to pass a signal displaying a stop indication. Ask another question about the information I just provided as I need points.

Answer 2

Red Means Stop..
Yellow - Next signal at red, prepare to stop
Flashing Yellow - for High Speed Trains - Diveriging at junction ahead
Double Yellow - Next signal at yellow - prepare to slow down
Green - Clear ahead
Flashing Green - High Speed Train - Higher Speeds allowed

Answer 3

You mean the signals?

Red = Stop
Single yellow = prepare to stop at next signal
Double yellow = slow down and prepare for a single yellow at next signal
Green = all clear, full speed ahead

Remember it takes a long time for a train to stop, so they need advance warning of an approaching red signal

Answer 4

the different color lights tell the engineers how far away a train is ahead of them...red means there is a train that is very close and he has to stop or slow down, yellow means there's a train a little ways ahead and he needs to slow down, green means he's all clear to continue

Answer 5

Your right! Red, yellow, and green. Just like for autos. Even though train progress is monitored by dispatchers who keep track of their location and can radio the engineers to let them know what's going on, the lights tell the engineer what's up ahead. Green for all clear, yellow for another train well ahead, and red for another one not so far ahead. I don't know what the distance criteria are, but that's it in a nutshell.

Answer 6

The variety of indications vary railroad to railroad depending on what signals the line is equipped with. Some have a simple red-yellow-green system, others have multiple signal heads for other indications.

Here's an official source, with pictures. NORAC is used by many railroads, freight and passenger.

Use this link -- pictures and all:

http://www.vnerr.com/training/signal_asp...

Just for the hell of it, here are the rules regarding cab signals if so equipped.

http://www.vnerr.com/training/cab_signal...

Answer 7

red means stop yellow means be prepared to stop and green means keep on going no trains ahead.

Answer 8

To inform any one that is trespassing on the property of the railroad that a train is in fact coming and if you don't move your feet you may be statistic number 1,253 for that year.

CHoo, Choooooo!