From: jps@dworkin.wustl.edu (James Sterbenz)
Newsgroups: rec.railroad
Subject: Re: Railroad Signals
Date: 15 Dec 92 22:27:58 GMT
Organization: Washington University,  St Louis MO

In article <1gl3udINN7a1@hp-col.col.hp.com> tvervaek@col.hp.com (Tom Vervaeke) writes:
>Could someone recommend a good book to assist me in learning railroad
>signalling? I'm guessing there is a WIDE variety of signals and
>semaphores out there. I'm tired of being ignorant of this system. I live
>in CTC territory and still haven't figured it out. I think the extent of
>my knowledge is this:          

>    * When the signal is not lit at all, there are no trains in the
>      block.

This is "approach lit" signaling, which means that the signal is lit
only when necessary to be seen by a train -- very boring for those of
us who like to see signals lit!

>    * When the signal is on there is a train somewhere in the block but
>      I can't tell which direction.

Depends on the particular system, but it would not be directional.  In 
some cases I've seen only the signals light for one of multiple tracks,
in others all the track's signals will come on (slightly better from a
safety standpoint).  

>
>    * Green means proceed, red means stop, yellow means slow or caution.
>

It really reflects the occupancy of the block (and in the case of interlockings
the setting of a route and switch points).  Green indicates clear (next 2
blocks clear); yellow indicates approach (next block clear, second block
occupied -- prepare to stop at next signal and usually in North America
immediately reduce to medium speed); red indicates stop (block occupied
or interlocking route not set).  It really gets a lot more complicated than
this, particularly with multi-head signals that apply to interlockings
that have routes of multiple speeds.  I really only described what a block
signal does.  We really nead a FAQ reply for this, but I can send you a
(somewhat non-tutorial) summary of North American signal types I posted
a while back (the full full article seems to be eternally not yet done :-)

>Here's a specific question: Locally we have simply signal light towers 
>that look like this: (I'm not an artist): 
>
>      -----
>      | O |  This is a 10' tall       
>      |   |  signal tower with
>      -----  two lights, green or
>      |   |  red usually. 
>      | O |
>      -----
>        |
>	|
>	|
>	|
>      -----
>
>      This is the kind of signal at Palmer lake on the northbound
>      portion of the signal track just below the switch leading to the
>      double track. Once the track goes to double the track on the right
>      is generally (almost always?) used for northbound traffic, while
>      the left is used for southbound.  Could someone inform me what the
>      possible light combinations might mean?

I assume that this is a 2-head searchlight signal; each light can be
(typically) red, green, or yellow.  The upper lamp applies to the 
normal speed straight route, thus 
G = clear   Y = approach   R = stop (and stay)
R           R              R

The lower lamp is non-red when the switch is set to diverge requiring a
reduction to medium speed (depends on the railroad), thus
R = medium clear, i.e. the switch is set for the diverging route and 
G      2 blocks are free; pass through the interlocking at medium speed.s 

R = medium approach (diverging route prepared to stop at next signal --
Y      and it may mean restricting, but lets keep it simple for now...)  
--
James Sterbenz  IBM HPCC       (High Performance Computing and Communications)
                472 Wheelers Farms Rd. MS93           jpgs@watson.vnet.ibm.com
                Milford CT 06460-1844 USA                      +1 203 783 4380

Newsgroups: rec.railroad