games/devtest/mods/basetools/textures/basetools_stonepick.png

#LyX 2.2 created this file. For more info see http://www.lyx.org/
\lyxformat 508
\begin_document
\begin_header
\save_transient_properties true
\origin unavailable
\textclass paper
\use_default_options true
\maintain_unincluded_children false
\language english
\language_package default
\inputencoding auto
\fontencoding global
\font_roman "default" "default"
\font_sans "default" "default"
\font_typewriter "default" "default"
\font_math "auto" "auto"
\font_default_family default
\use_non_tex_fonts false
\font_sc false
\font_osf false
\font_sf_scale 100 100
\font_tt_scale 100 100
\graphics default
\default_output_format default
\output_sync 0
\bibtex_command default
\index_command default
\paperfontsize default
\spacing single
\use_hyperref false
\papersize default
\use_geometry true
\use_package amsmath 1
\use_package amssymb 1
\use_package cancel 1
\use_package esint 1
\use_package mathdots 1
\use_package mathtools 1
\use_package mhchem 1
\use_package stackrel 1
\use_package stmaryrd 1
\use_package undertilde 1
\cite_engine basic
\cite_engine_type default
\biblio_style plain
\use_bibtopic false
\use_indices false
\paperorientation portrait
\suppress_date false
\justification true
\use_refstyle 1
\index Index
\shortcut idx
\color #008000
\end_index
\leftmargin 1cm
\topmargin 1cm
\rightmargin 1cm
\bottommargin 1cm
\secnumdepth 3
\tocdepth 3
\paragraph_separation indent
\paragraph_indentation 0bp
\quotes_language english
\papercolumns 1
\papersides 1
\paperpagestyle default
\tracking_changes false
\output_changes false
\html_math_output 0
\html_css_as_file 0
\html_be_strict false
\end_header

\begin_body

\begin_layout Title
Minetest Mod - Advanced Trains [advtrains]
\end_layout

\begin_layout Title
Interlocking System Guide
\end_layout

\begin_layout Section
Introduction
\end_layout

\begin_layout Standard
In real-world railways, a so-called interlocking system is a set of railway
 signals and trackside equipment.
 Its purpose is to prevent conflicting train movements which otherwise could
 result in derailing or colliding trains.
 If you want more information, just search for 
\begin_inset Quotes eld
\end_inset

railway interlocking
\begin_inset Quotes erd
\end_inset

 on the internet.
\end_layout

\begin_layout Standard
Real-world interlocking systems perform this task by setting routes.
 A route is a path along a track that a train can safely pass.
 To set a route for a train, the signalman (the operator of a signal box)
 has to set switches (turnouts) to the correct position and lock them in
 order to make a signal for a train show 
\begin_inset Quotes eld
\end_inset

Proceed
\begin_inset Quotes erd
\end_inset

.
 In newer systems, this is done automatically by the interlocking system.
 A route can not be set if switches are locked to a wrong position by another
 route or if any portion of the route is occupied by a train.
\end_layout

\begin_layout Standard
The interlocking system in this Minetest mod tries to follow real-world
 interlocking systems as far as applicable.
 It divides tracks into track sections and implements a route setting mechanism
 following the same principle.
\end_layout

\begin_layout Standard
However, for the sake of simplicity of implementation and usage, not all
 concepts of real-world interlocking have been taken over.
 Especially, there is no mechanism for overlap.
\end_layout

\begin_layout Standard
If you are looking for a place to learn how real-world interlocking systems
 work, have a look at 
\begin_inset Quotes eld
\end_inset

SimSig
\begin_inset Quotes erd
\end_inset

.
 By looking at their simulations, you can obtain experience on how to set
 up your own interlocking systems in AdvTrains.
 The SimSig glossary is a good place to look up unknown terms in this document.
\end_layout

\begin_layout Section
Setting up track sections
\end_layout

\begin_layout Standard
In the real world, a line of track is divided into so-called track sections,
 or track circuits.
 Those systems often can not tell where exactly a train is, but only which
 track sections it occupies.
 A route can never be set through an occupied track section.
\end_layout

\begin_layout Standard
A track section often covers:
\end_layout

\begin_layout Itemize
A section on a main running line, between two signals
\end_layout

\begin_layout Itemize
A single turnout
\end_layout

\begin_layout Itemize
A rail crossing, or a set of turnouts acting as a double/single slip switch
\end_layout

\begin_layout Itemize
A siding
\end_layout

\begin_layout Standard
You will find some examples on how to interlock certain patterns later.
\end_layout

\begin_layout Subsection
Track Circuit Breaks
\end_layout

\begin_layout Standard
In this mod, you will not directly configure the locations of track sections.
 Instead, you designate the borders of each track section using a special
 node, the Track Circuit Break, abbreviated TCB.
\end_layout

\begin_layout Standard
For example, if you want to create a track section for a piece of a main
 running line, you set up two TCBs at the ends of this track circuit.
\end_layout

\begin_layout Standard
Setting up a TCB works as follows:
\end_layout

\begin_layout Enumerate
Place a TCB node somewhere near the place where the circuit break is going
 to be located.
\end_layout

\begin_layout Enumerate
Right-click the TCB node
\end_layout

\begin_layout Enumerate
Punch the rail which should act as TCB
\end_layout

\begin_layout Standard
The result should look like this:
\end_layout

\begin_layout Standard
\begin_inset Graphics
	filename lyx_img/screenshot_20180830_142551.png
	width 10cm

\end_inset


\end_layout

\begin_layout Standard
Now you have assigned the TCB node to a rail.
 Right-click the TCB node once again.
 This will bring up a form which looks as follows:
\end_layout

\begin_layout Standard
\begin_inset Graphics
	filename lyx_img/Bildschirmfoto_2018-08-30_14-26-35.png
	width 10cm

\end_inset


\end_layout

\begin_layout Standard
You see that the form is divided in side A and side B.
 To designate where each side is, a marker is displayed on the rail.
 You can always make this marker show up by punching the TCB node, and remove
 it by punching the marker.
 Both sides are shown as 
\begin_inset Quotes eld
\end_inset

End of interlocking
\begin_inset Quotes erd
\end_inset

.
 This means that there is no track section set up at this place.
\end_layout

\begin_layout Standard
You should repeat this procedure once again a few meters away from the first
 TCB to create a second TCB on the same track.
\end_layout

\begin_layout Standard
\begin_inset Graphics
	filename lyx_img/Bildschirmfoto_2018-08-30_14-32-48.png
	width 10cm

\end_inset


\end_layout

\begin_layout Standard
Once you have both bordering TCBs set up, you can now create the actual
 track section.
 To do this:
\end_layout

\begin_layout Enumerate
Right-click one of the TCBs
\end_layout

\begin_layout Enumerate
Locate the correct side (A or B) to create the track section
\end_layout

\begin_layout Enumerate
Click 
\begin_inset Quotes eld
\end_inset

Create interlocked Track Section
\begin_inset Quotes erd
\end_inset

 in the formspec on the chosen side.
\end_layout

\begin_layout Standard
Now, the text on the formspec has changed.
 It shows something like this:
\end_layout

\begin_layout Standard
\begin_inset Graphics
	filename lyx_img/Bildschirmfoto_2018-08-30_14-27-25.png
	width 5cm

\end_inset


\end_layout

\begin_layout Standard
Clicking 
\begin_inset Quotes eld
\end_inset

Show Track Section
\begin_inset Quotes erd
\end_inset

 brings up another formspec:
\end_layout

\begin_layout Standard
\begin_inset Graphics
	filename lyx_img/Bildschirmfoto_2018-08-30_14-28-32.png
	width 5cm

\end_inset


\end_layout

\begin_layout Standard
On the top, you see a list of all TCBs that border this track section.
 In your case, there should be two TCBs listed.
 If there's only one, head over to 
\begin_inset CommandInset ref
LatexCommand ref
reference "subsec:Long-track-sections,"

\end_inset

.
 You should now select a name for the track section, to identify it later.
\end_layout

\begin_layout Standard
The same procedure is applicable when you create a turnout track section,
 except that you have to set up three or more TCBs.
\end_layout

\begin_layout Standard
The AdvTrains interlocking system allows you to add more TCBs after you
 have created a track section.
 This works without problems in most cases.
 For example, you can easily insert a turnout into an already set-up track
 section and create another TCB behind it, and AdvTrains will automatically
 detect the existing track section.
 Problems arise only if you try to insert a TCB in-between a section, in
 which case both sides of the TCB will end up assigned to the same section.
 The code currently does not handle this case properly, so try to avoid
 this situation by all means.
 As a last resort, you can always dissolve a faulty track section, as described
 in the next chapter.
\end_layout

\begin_layout Subsection
Long track sections, crossings and other edge cases
\begin_inset CommandInset label
LatexCommand label
name "subsec:Long-track-sections,"

\end_inset


\end_layout

\begin_layout Subsubsection
Very long track sections
\end_layout

\begin_layout Standard
If you try to set up a track section that is longer than 1000 nodes, advtrains
 won't recognize the TCB at the other end because of a safety limit in the
 traverser function, which is supposed to prevent deadlocks.
 This case has happened when the Track Section overview screen only shows
 one TCB in the list.
 The procedure for this is as follows:
\end_layout

\begin_layout Enumerate
Go to the second TCB (the one that wasn't recognized).
 It should show 
\begin_inset Quotes eld
\end_inset

End of Interlocking
\begin_inset Quotes erd
\end_inset

 on the relevant side.
\end_layout

\begin_layout Enumerate
Click 
\begin_inset Quotes eld
\end_inset

Create interlocked track section
\begin_inset Quotes erd
\end_inset

.
 The section created will be different from the one that is already present.
\end_layout

\begin_layout Enumerate
In the track section overview, click 
\begin_inset Quotes eld
\end_inset

Join into other section
\begin_inset Quotes erd
\end_inset


\end_layout

\begin_layout Enumerate
Go back to the first TCB, bring up the Track Section overview screen of
 the first track section and click 
\begin_inset Quotes eld
\end_inset

Join with ???
\begin_inset Quotes erd
\end_inset


\end_layout

\begin_layout Standard
The other, missing TCB should now appear in the list.
 If you accidentally started such a joining procedure, click the 
\begin_inset Quotes eld
\end_inset

X
\begin_inset Quotes erd
\end_inset

 button on the right.
\end_layout

\begin_layout Subsubsection
Rail crosses
\end_layout

\begin_layout Standard
Since rail crosses are created by laying tracks across each other without
 logical connection, there's no way for advtrains to know whether rails
 cross each other.
\end_layout

\begin_layout Standard
Rail crossings in interlocking systems are always one single track section,
 which in most cases has 4 TCBs adjacent.
\end_layout

\begin_layout Standard
\begin_inset Graphics
	filename lyx_img/Bildschirmfoto_2018-08-30_14-51-25.png
	width 5cm

\end_inset


\end_layout

\begin_layout Standard
The procedure is quite similar to the one for long sections: First, create
 two track sections for the branches, and then use the 
\begin_inset Quotes eld
\end_inset

Join
\begin_inset Quotes erd
\end_inset

 function to merge both sections into one.
\end_layout

\begin_layout Subsubsection
Deleting and re-adding single TCBs to a section
\end_layout

\begin_layout Standard
In some occasions, for example when you remove a siding or a crossover,
 it can be necessary to unassign a TCB from a track section.
 There are multiple ways to do this:
\end_layout

\begin_layout Itemize
In the TCB form, click the 
\begin_inset Quotes eld
\end_inset

Remove from section
\begin_inset Quotes erd
\end_inset

 button
\end_layout

\begin_layout Itemize
In the track section form, first select the TCB in the list and then click
 
\begin_inset Quotes eld
\end_inset

Unlink selected TCB
\begin_inset Quotes erd
\end_inset


\end_layout

\begin_layout Standard
The result is that the TCB shows 
\begin_inset Quotes eld
\end_inset

End of Interlocking
\begin_inset Quotes erd
\end_inset

 and the section does not list the TCB as an endpoint anymore.
\end_layout

\begin_layout Standard
The other case is adding a siding or a crossover, in which case one or more
 TCBs still show 
\begin_inset Quotes eld
\end_inset

End of Interlocking
\begin_inset Quotes erd
\end_inset

 although they should be part of a section:
\end_layout

\begin_layout Itemize
Go to another TCB that is registered in the track section and click 
\begin_inset Quotes eld
\end_inset

Update near TCBs
\begin_inset Quotes erd
\end_inset


\end_layout

\begin_layout Itemize
If that did not work, follow the procedure of creating a long track section
\end_layout

\begin_layout Subsubsection
Dissolving sections
\end_layout

\begin_layout Standard
If you made a mistake setting up something and you don't see any other way
 to fix a misconfigured track section, you can always delete it using the
 
\begin_inset Quotes eld
\end_inset

Dissolve section
\begin_inset Quotes erd
\end_inset

 button.
 This operation removes the track section and sets all TCBs that previously
 belonged to the section as 
\begin_inset Quotes eld
\end_inset

End of Interlocking
\begin_inset Quotes erd
\end_inset

.
 This will always work and lets you start over new with setting up track
 sections.
\end_layout

\begin_layout Subsection
Interlocking patterns
\end_layout

\begin_layout Standard
This section shows some examples on how you should set up track sections
 on certain track configurations.
\end_layout

\begin_layout Section
Signals and routes
\end_layout

\begin_layout Standard
The purpose of signals is to inform trains about whether they can proceed
 into the next section safely.
 Making a section of track safe to pass for a train, turnouts need to be
 set to the correct position and no other train should be allowed to cross
 or share parts of the route with this train.
\end_layout

\begin_layout Subsection
Assigning Signals to TCBs
\end_layout

\begin_layout Standard
Signals in the advtrains interlocking system are positioned - like in real
 life - at the border of track sections.
\end_layout

\begin_layout Standard
When you set up a signal, do the following steps:
\end_layout

\begin_layout Enumerate
If not already happened, set up a TCB (you don't need to, but are advised
 to, configure track sections there)
\end_layout

\begin_layout Enumerate
Place the signal a few meters in front of the TCB, so that trains stopping
 at the signal do never pass the TCB
\end_layout

\begin_layout Enumerate
Locate the side of the TCB which points in the direction that trains will
 proceed past the signal, as shown in the figure below.
\end_layout

\begin_layout Enumerate
Right-click the TCB, and click 
\begin_inset Quotes eld
\end_inset

Assign a signal
\begin_inset Quotes erd
\end_inset

 on this side.
\end_layout

\begin_layout Enumerate
Punch the signal.
\end_layout

\begin_layout Standard
\begin_inset Graphics
	filename lyx_img/assign_signal.png
	width 8cm

\end_inset


\end_layout

\begin_layout Standard
You can assign a signal to each side of a TCB.
 This is, for example, useful when creating block sections on a bi-directional
 main running line.
\end_layout

\begin_layout Subsection
The concept of routes
\end_layout

\begin_layout Standard
A so-called route is a locked path between two signals, which locks all
 turnouts in the correct position.
\end_layout

\begin_layout Standard
Example: Imagine a station with 2 platforms on a single track running line.
 We are looking at signal A.
 You probably want trains coming from the right to go into platform 1 or
 into platform 2, so you need to program 2 routes.
\end_layout

\begin_layout Standard
\begin_inset Graphics
	filename lyx_img/route_ex1.png
	width 7cm

\end_inset


\end_layout

\begin_layout Standard
This leads us to the most important aspect of route programming: Routes
 always start at a signal (A) and end at a signal facing in the 
\series bold
same direction
\series default
 (D and E), not at an opposite-facing signal (B and C).
 There are only few exceptions, we'll cover this later.
\end_layout

\begin_layout Standard
When you set a route to make a train proceed on it, the interlocking system
 ensures that:
\end_layout

\begin_layout Itemize
There are no rail vehicles on the route
\end_layout

\begin_layout Itemize
All turnouts are set to the correct position and it is impossible to move
 them
\end_layout

\begin_layout Itemize
No other routes can be set that would in any way conflict with this route
\end_layout

\begin_layout Standard
For this to work, you need to specify all track sections the train will
 pass along, as well as the positions of all turnouts that need to be locked.
 Those are not only the turnouts that lay directly on the train's route,
 but also some turnouts on adjacent tracks, the so-called flank protection.
\end_layout

\begin_layout Standard
The purpose of flank protection is to prevent runaway trains and/or wagons
 to pass into a route.
 This is achieved by setting nearby turnouts to a position that points 
\begin_inset Quotes eld
\end_inset

away
\begin_inset Quotes erd
\end_inset

 from the route.
 Example:
\end_layout

\begin_layout Standard
\begin_inset Graphics
	filename lyx_img/route_ex2.png
	width 7cm

\end_inset


\end_layout

\begin_layout Standard
The upper turnout, of course, needs to be locked in straight (normal) position,
 while the lower one is not relevant for the route itself.
 But what if the lower turnout was set to the diverging (reverse) position
 and the driver of another train approaching signal B fails to see the red
 light? This train would crash into the first one.
 To minimise danger, that other train would need to be routed towards signal
 D.
\end_layout

\begin_layout Standard
There are, of course, situations, where both positions of a turnout would
 conflict with a route equally.
 In those situations, there's nothing you can do and no flank lock needs
 to be set.
\end_layout

\begin_layout Subsection
Shunt routes
\end_layout

\begin_layout Standard
Operating railways is not all about driving trains around.
 Coupling, decoupling and moving single engines, wagons or groups of wagons
 across a station, called shunting, also plays an important role.
\end_layout

\begin_layout Standard
Remember what we said about routes: There must be no rail vehicles on the
 route.
 So what if you have some goods wagons ready on a siding, and want to couple
 an engine to it? You can not set a regular route into the siding, because
 it is occupied.
\end_layout

\begin_layout Standard
The solution is to program a second route into the siding, but with the
 difference that it already ends at the rear-facing signal of it, so it
 doesn't include the siding section itself:
\end_layout

\begin_layout Standard
\begin_inset Graphics
	filename lyx_img/route_ex3.png
	width 7cm

\end_inset


\end_layout

\begin_layout Standard
The Sht2 route then needs to show a shunt aspect, which instructs the driver
 to proceed slowly and watch out for vehicles on the route.
 To show a 
\begin_inset Quotes eld
\end_inset

free
\begin_inset Quotes erd
\end_inset

 aspect here would be wrong, because that would mean that the track is free
 until the next main signal, which it is clearly not.
\end_layout

\begin_layout Standard

\shape italic
Note that advtrains_interlocking currently does not allow to set individual
 aspects for routes, this is a feature still to be implemented soon.
\end_layout

\begin_layout Standard
Shunt routes like this are, so far, the only exception to the 
\begin_inset Quotes eld
\end_inset

Routes should end at a signal facing the same direction
\begin_inset Quotes erd
\end_inset

 rule.
\end_layout

\begin_layout Subsection
Route Release
\end_layout

\begin_layout Standard
In early real-life interlocking systems, routes either had to be cancelled
 by the signalman after the train had passed the route, or there was a single
 release contact at the end of the route.
 However, as interlocking systems evolved and the position of trains is
 now roughly known by the track sections, portions of the route can be freed
 as soon as the train has left the corresponding section.
\end_layout

\begin_layout Standard
AdvTrains has chosen a modern approach to route releasing.
 Each turnout lock is associated to a track section belonging to the route's
 path.
 Once the train leaves this section, all assigned locks are also freed.
\end_layout

\begin_layout Subsection
Programming a route
\end_layout

\begin_layout Standard
The route programming procedure is quite straightforward if you've read
 the previous sections and understood how routes should be set.
\end_layout

\begin_layout Standard
Routes always start at a signal.
 You must have assigned the signal to a TCB, as described earlier.
\end_layout

\begin_layout Standard
When you right-click the signal, it no longer changes its aspect.
 Instead, a formspec pops up, showing you an (empty) list of routes with
 the possibility to set them or to create new routes.
 Click the 
\begin_inset Quotes eld
\end_inset

Create new route
\begin_inset Quotes erd
\end_inset

 button to start programming a new route.
\end_layout

\begin_layout Standard
The form closes, and an arrow is displayed on the TCB.
 You are now in 
\begin_inset Quotes eld
\end_inset

Route Programming
\begin_inset Quotes erd
\end_inset

 mode, programming the first track section of the route.
 Now:
\end_layout

\begin_layout Itemize
Put any turnouts you need to lock in the correct position (e.g.
 by right-clicking them).
 This includes flank protection.
\end_layout

\begin_layout Itemize
Punch them.
 This makes a marker with a blue lock symbol appear.
\end_layout

\begin_layout Itemize
If you punch a turnout again, or punch the marker, you can remove the lock
 again.
\end_layout

\begin_layout Itemize
When you've locked all turnouts in the current section, go to and punch
 the TCB that is the border to the next track section the train proceeds
 into.
\end_layout

\begin_layout Standard
Depending on the situation, you are now offered some possibilities to proceed:
\end_layout

\begin_layout Itemize
Click the 
\begin_inset Quotes eld
\end_inset

Advance to next section
\begin_inset Quotes erd
\end_inset

 button if your route consists of more sections with turnouts to lock, and
 you need to continue programming.
 Follow the above steps to set locks for the next section.
\end_layout

\begin_layout Standard
Once you've clicked the 
\begin_inset Quotes eld
\end_inset

Advance
\begin_inset Quotes erd
\end_inset

 button, the lock markers change to a red lock symbol, telling they can't
 be changed anymore.
 Repeat the above procedure until you are ready to complete the programming
 procedure:
\end_layout

\begin_layout Itemize
Click the 
\begin_inset Quotes eld
\end_inset

Finish route HERE
\begin_inset Quotes erd
\end_inset

 button when you've set up the locks for the last track section of the route
 and punched the final TCB (the one with the next signal).
 You will be asked for a route name and your route will be saved.
\end_layout

\begin_layout Itemize
The 
\begin_inset Quotes eld
\end_inset

Finish route at end of NEXT section
\begin_inset Quotes erd
\end_inset

 button (third button) is an useful quickhand to make the route proceed
 one more section.
 Using this button is equivalent to first clicking the 
\begin_inset Quotes eld
\end_inset

Advance
\begin_inset Quotes erd
\end_inset

 button, then flying to the end of the next track section and finishing
 the route there.
 You can not (officially) set turnout locks in the final section using this
 method.
\end_layout

\begin_layout Standard
A few hints:
\end_layout

\begin_layout Itemize
If one turnout should be locked by more than one section, set the lock only
 in the 
\family typewriter
\series bold
last
\family default
\series default
 of those sections.
 Locking the same turnout in multiple sections of a single route results
 in undefined behavior!
\end_layout

\begin_layout Itemize
If you accidentally advanced the route wrongly, you can use the 
\begin_inset Quotes eld
\end_inset

Step back one section
\begin_inset Quotes erd
\end_inset

 button to undo this.
\end_layout

\begin_layout Itemize
If you want to stop programming the entire route without saving it, use
 the 
\begin_inset Quotes eld
\end_inset

Cancel route programming
\begin_inset Quotes erd
\end_inset

 button.
\end_layout

\begin_layout Itemize
The third button is especially useful for programming simple block sections
 on a main running line, since you can stay at the starting signal (punch
 starting TCB and select third button).
\end_layout

\begin_layout Itemize
If a route should end in a dead end, you MUST use the 
\begin_inset Quotes eld
\end_inset

Finish in NEXT section
\begin_inset Quotes erd
\end_inset

 button, because there is no final TCB that you could punch.
\end_layout

\begin_layout Itemize
The third button does NOT work on sections with more than 2 exits, because
 the system won't be able to determine the final TCB of the route then.
\end_layout

\begin_layout Section
Interlocking system operation
\end_layout

\begin_layout Standard
Setting up the interlocking for a portion of a railway network requires
 some time, experience and planning, but once done, there's not much to
 do anymore to make trains run on your, now safer, railway.
 This section covers some useful practices to route trains across your network.
\end_layout

\begin_layout Standard
At the moment, routes can only be set by clicking the signal or via LuaATC,
 except if you use automatic working.
 It is planned to control this via the onboard computer and via a 
\begin_inset Quotes eld
\end_inset

signal box
\begin_inset Quotes erd
\end_inset

 view based on the currently broken itrainmap.
\end_layout

\begin_layout Subsection
Simple route setting and cancelling
\end_layout

\begin_layout Standard
To set a route, simply right-click the signal, select a route and click
 
\begin_inset Quotes eld
\end_inset

set route
\begin_inset Quotes erd
\end_inset

.
 If there are no conflicts, the signal turns green and the train is allowed
 to proceed.
\end_layout

\begin_layout Standard
It may be possible that the route can not be set, because one or more other
 routes conflict with the current one, or a section is blocked.
 In this case, the signal stays red, and the conflicting item is shown in
 the formspec.
 As soon as the conflict is resolved (by cancellation or release of the
 conflicting route, or the section becoming free), the requested route will
 be set and the signal turns green.
\end_layout

\begin_layout Standard
If a route is either requested or set, it can be cancelled from the signalling
 formspec.
 This means that all turnouts and sections are released, and the signal
 reverts back to red.
 This of course only works when the train has not passed the signal yet.
 There is no mechanism for Approach Locking.
\end_layout

\begin_layout Subsection
Automatic Working
\end_layout

\begin_layout Standard
Block signals on main running lines usually only have a single route to
 set, the one proceeding along the main line.
 Their purpose is only to show whether there are trains in the next section.
ofs	hex dump	ascii
0000	89 50 4e 47 0d 0a 1a 0a 00 00 00 0d 49 48 44 52 00 00 00 10 00 00 00 10 08 03 00 00 00 28 2d 0f	.PNG........IHDR.............(-.
0020	53 00 00 00 0f 50 4c 54 45 00 00 00 42 22 09 5d 3d 24 6d 6d 6d 92 92 92 a8 f1 d8 f4 00 00 00 01	S....PLTE...B".]=$mmm...........
0040	74 52 4e 53 00 40 e6 d8 66 00 00 00 3a 49 44 41 54 78 da 6d cc 41 0e 00 20 08 03 41 a5 fc ff cd	tRNS.@..f...:IDATx.m.A.....A....
0060	56 e3 65 1b 7a db 21 61 0d 6b 2f 48 b2 25 69 20 4a 55 48 6d 49 e8 f7 1b 7d 85 6d 60 5b 1a 6d 10	V.e.z.!a.k/H.%i.JUHmI...}.m`[.m.
0080	db 12 fd ef 5c f6 01 61 ba 00 9a ef 41 19 67 00 00 00 00 49 45 4e 44 ae 42 60 82	....\..a....A.g....IEND.B`.