The NYCTA has tracks where the direction of traffic may be reversed. The GRS and US&S interlocking machines use a lever painted Blue to control the direction of traffic. This lever locks the opposing signals so a train cannot enter from the wrong direction. The levers have to be in sync at the towers at both ends of the reversing section. If you do have a reversing section, a lever can be used to reverse the track power instead of an AR unit.
The express tracks loop back on each other, but of course only the portions shown are on this model board. It is to be assumed that there are seperate interlocking plants for both Lenox Avenue and for Nevins Street. There are none, they just loop back on each other in the same direction they were going, but there are crossings that will move trains to and from the local and express tracks.
As for the Mane Lion, there surely is "continious" running, but the tower operator must be a juggler. Him can have five or six trains out on the road, but must keep making room for incoming by dispatching the outgoing. There are layup pockets for parking trains at night when headway is increased to 20 minuytes and the work trains come out to play.
The mane line surey does look like a reversing loop, but electrically it is not. The double crossover at 242nd Street is completely electrically dead, and the terminal tracks are powered by whatever track they are aligned with.
Since my trains have 48 wheel pickup, I figured the heck with trying to wire the crossover.
ROAR
The Route of the Broadway Lion The Largest Subway Layout in North Dakota.
Here there be cats. LIONS with CAMERAS
As shown on the model board, the whole layout is one big reverse loop. The crossover on the far left make it so. I assume there's more, because if the model board schematic is accurate, there's no place for continuous running there. Or is there no continuous running?
--Randy
Modeling the Reading Railroad in the 1950's
Visit my web site at www.readingeastpenn.com for construction updates, DCC Info, and more.
LION likes interlocking plants. And it helps make sense out of a model railroad. It really does help visualize reversing loops and wyes. It also demonstrates how to gap and block a reversing loop, since if a track returns from the east end to the west end, then it is a reversing loop and that is the track that requires proper gaps for electrical continuity.
Interlocking machines, from the steam era, and still operated into this century, are an integrated whole. The interlocking machine, the switch machines, and the signals are all made by the same company and cannot be used with other kinds of equipment.
The most ancient, and possibly well known is the US&S "armstrong" machine. That is to say the old levers in which the wherewithall for moving a set of switchpoints comes from the box of Wheaties that the operator had for breakfast. This wouold not need to show up in a discussion on the Electronics forum escept of course, that we do use electric parts to make our railroads work, and knowing what they did helps us to know what we want to do, even if we are just going to use electric switches.
On the "Armstrong Machine", two levers must be moved to align a set of switchpoints. First a lever must be used to unlock the switch points, then a second lever is used to move the switch points, and finally the first lever must be returned to the lockied position. If one of these levers cannot be moved (The lock for example) there may be a chunck of ice or a piece of ballast that is blocking the movement. The tower operator will have to go down to the tracks and correct this, and then come back to the tower to make the lever movements. If the point lever will not move, or the lock cannot be unlocked, then the machine itself is controling the situation with a bed of heave brass rods under the floor of the tower that prevent settting up a conflicting alignment. Once the plant is fully aligned, the the signal levers can be moved to give a train aughority to pass through the plant.
The Electric aparatus of the General Railway Signal system (GRS) uses electricity rather than mechanical rods along the tracks to effect the movement of the switchpoints. The locks work together with the switch points, and if a lock after a lever movement has been started cannot be obtained the lever cannot be fully reversed, and the signal lever would also remain locked. Here one lever can move two switch points at once, but each apparatus must have its own space on the interlocking machine, as the machine handles each set of points and locks independently.
The powered US&S machines were electro-pnumatic in nature, with electricity in the tower, and air pressure to move the points. These levers have neutral position to save air pressure. So move the lever one way to set up normal movement, move the lever the other way to set up a reverse movement. Center the lever to close the air valves. (Think of using a "center-off" toggle swithc to run your Tortoise.) All levers must be correct before a signal can be cleared.
Since I have built a model of a GRS machine, I will use that model here. The Interlocking Plant consists of three distinct components. In the tower is the frame or machine itself. It holds the levers and their apratus and the physical interlocking bars that supervise lever movements. It also holds the Modelboard which displays the movements of trains approaching the plant and as they move through the plant. A train clearing a circuit will free the levers behind it to move once again. (If the Train does not appear, a whole big deal must be set up to clear the levers sans the train.)
Below is a "row of levers" Actually automotive toggle switches for the purpose of model building (unless you want to build a big machine for yourself). They are laid out as they would be on a GRS machine. Red levers are for signals, and the black levers are for the switch points. The red levers on the left (1, 2, 3, 4) control movements from left to right including the exit signals for the outbound train. The red levers on the right (13, 14, 15, 16) control movement from from rith to left through the plant. The black levers (5 - 12) control the plant from left to right and corespond to the numbers on the modelboard.
Levers in the down position are NORMAL, levers in the up position are "REVERSED". Typically a reversed point lever represents a diverging route. Signals levers in the normal position display a RED SIGNAL. Reversing the lever clears the signal.
And this is the modelboard that goes with this plant. The same machine can be used for any plant, how it is aranged and set up is exclusive to each insatallation, thus the model board is "typical" where as the machine is generic.
We can assume, for simplicity, that north is up, west is left and east is right, but of course that depends on how the railroad oriented its tracks and towers. Assuming that trains can run in either direction on the main line, giving a train a CLEAR signal out of this plant would LOCK the next plant down the line. An opposing movement could not be set up there.
Note that levers 5 and 12 operate two sets of switchpoints in unison.
Drawing this out while building your railroad, (is fun, according to me) will clearly illuminate any reversing tracks that you may create, and will demonstrate how to control and signal them. Maybe it is fun to just let a train run around your loops, but if you have a reversing loop, then you will have to control it. I think that the interlocking plant is the most interesting part of the operation. But then, what the heck, I am a LION, so what do I know.
Above is my GRS machine, and its model board. My lever colors are not "generically correct" so do not use that for guidance. (Red levers are signals, green levers are main line switch points, and yellow levers are non-revenue switch points, and trains with passengers can never be aligned across them.) The modelboard here is inoperative, but does diagram my entire layout. Is there a reversing loop hidden in there, and if so, how might it be controlled?