Wayside and crossing signal circuits

Trains Magazine General Discussion
1

Hi Guys,
I have a friend who has a question, in several parts, about the way a wayside signal and crossing signals get both power for the signal, and how they “read” where the train is. I can answer them, but only in very general terms, and he wants specific answers, which I cant provide.

I know there is a signal maintainer, and several electrical engineers here, so I pose the question to you.

How does the current in the rails keep from getting grounded by the spikes and ties, what type of current, A/C or D/C is used, at what voltage, amps and frenquency is it at, and how does the signal read the location of the train?.

Where do the signals, both wayside, and grade crossing, get the power for the lights and equipment?(I knew this one)

Please be specific as you can, numbers and details is what he is looking for.

No, he is not a sabatour, terrorist or madman, just a kid with a active and questioning mind and some legimate questions.

And before you all go,“but dont all you railroad guys know how that stuff works?”
the answer is…
no we dont.[:0]
Most of the guys I work with couldnt tell you the difference between A/C or D/C, most of them think thats a heavy metal rock band.[8D]

Thanks in advance for your help,
You all Stay Frosty,
Ed

2

I’m no signal maintainer, but from what I vaguely remember from classroom discussions with the signals guy who was also our rules instructor, this applies to electrically insulated blocks. I may only have this partially right, so bear with me:

A DC current runs in both rails using positive leads and is grounded through the roadbed and a grounding cable, as your friend wondered. The circuit is based on a phase detection loop. When the train completes the shunt, the voltage drop triggers the relays, which switch the circuit to AC. This also provides the “flashing” lights.

Don’t know the specific voltage or amps, but would imagine the amperage is fairly low.

The signal doesn’t “read” the location of the train, it simply reads the block occupancy. On Conrail, whenever ther was a problem with the shunt, they called this an "“intermittent TOL” or “Track Occupancy Light” which would show up on their screens as a flashing track block, and this would alert them to areas where they needed to send police or signals maintenance.

ATS relay track occupancy to signals in front and behind the train (depending on whether it is 251 or 261 territory).

On in-cab signals, an induction coil is mounted ahead of the wheel of the locomotive, and this picks up modulation through the track on electrical currents which are piggy-backed at certain frequencies. The induction is detected from the field created between the wheels and the track.

PTC uses satellite tracking and GPS coordinates to constantly monitor actual train location and distance between trains, allowing for shorter blocks and/or more “flexible” block signalling.

Signal power is provided by electrical utility with failsafe battery backup.

Without going into the actual mechanics of the thing (so as not to provide others who may read this with sabotage information), the worst that is theoretically possible with signal failure is Restricted speed.

Hope this h

3

Hi Guys,
I have a friend who has a question, in several parts, about the way a wayside signal and crossing signals get both power for the signal, and how they “read” where the train is. I can answer them, but only in very general terms, and he wants specific answers, which I cant provide.

I know there is a signal maintainer, and several electrical engineers here, so I pose the question to you.

How does the current in the rails keep from getting grounded by the spikes and ties, what type of current, A/C or D/C is used, at what voltage, amps and frenquency is it at, and how does the signal read the location of the train?.

Where do the signals, both wayside, and grade crossing, get the power for the lights and equipment?(I knew this one)

Please be specific as you can, numbers and details is what he is looking for.

No, he is not a sabatour, terrorist or madman, just a kid with a active and questioning mind and some legimate questions.

And before you all go,“but dont all you railroad guys know how that stuff works?”
the answer is…
no we dont.[:0]
Most of the guys I work with couldnt tell you the difference between A/C or D/C, most of them think thats a heavy metal rock band.[8D]

Thanks in advance for your help,
You all Stay Frosty,
Ed

4

I’m no signal maintainer, but from what I vaguely remember from classroom discussions with the signals guy who was also our rules instructor, this applies to electrically insulated blocks. I may only have this partially right, so bear with me:

A DC current runs in both rails using positive leads and is grounded through the roadbed and a grounding cable, as your friend wondered. The circuit is based on a phase detection loop. When the train completes the shunt, the voltage drop triggers the relays, which switch the circuit to AC. This also provides the “flashing” lights.

Don’t know the specific voltage or amps, but would imagine the amperage is fairly low.

The signal doesn’t “read” the location of the train, it simply reads the block occupancy. On Conrail, whenever ther was a problem with the shunt, they called this an "“intermittent TOL” or “Track Occupancy Light” which would show up on their screens as a flashing track block, and this would alert them to areas where they needed to send police or signals maintenance.

ATS relay track occupancy to signals in front and behind the train (depending on whether it is 251 or 261 territory).

On in-cab signals, an induction coil is mounted ahead of the wheel of the locomotive, and this picks up modulation through the track on electrical currents which are piggy-backed at certain frequencies. The induction is detected from the field created between the wheels and the track.

PTC uses satellite tracking and GPS coordinates to constantly monitor actual train location and distance between trains, allowing for shorter blocks and/or more “flexible” block signalling.

Signal power is provided by electrical utility with failsafe battery backup.

Without going into the actual mechanics of the thing (so as not to provide others who may read this with sabotage information), the worst that is theoretically possible with signal failure is Restricted speed.

Hope this h