Simulation and Conflicts

Simulation and conflicts

Pressing Simulate in the schedule editor projects the schedule you are editing against every train currently on that rail network, and tells you what would happen.

The engine is deterministic: sorted train order, a fixed tick step, no wall clock, no random numbers. The same network state and the same schedule always produce the same result — which is what makes the conflicts worth arguing about.

What is simulated

The simulator mirrors Create 6.0.8:

• bang-bang acceleration/braking (v²/2a), so braking distance is Create's braking distance;
• per-tick section reservations, atomic chain-signal reservations, and persistent first-come-first-served claims;
• station dwells, and ScheduleRuntime's condition semantics — including CRN separation gates, seeded from CRN's own departure history;
• Tramways speed-sign zones, carried on the train through junctions with anticipatory braking.

Your edited schedule is driven by a phantom train — a copy of the train the schedule would run on. Everything else on the network is snapshotted from the live world and driven by its own schedule.

Known, deliberate differences from what Create does at runtime are listed in SIM_DIVERGENCES.md in the repository.

Setup window

Option	Meaning
Carriages / Locomotives	the phantom train's make-up (drives its acceleration and length)
Acceleration	None, Standard (applies Sim Acceleration Multiplier), or a custom value
Start time	Now, or a specific in-game hour/minute
Duration	how many in-game hours to simulate (1000 ticks per hour), capped by Sim Max Horizon Hours
Headway alert	minimum gap between consecutive trains through a section before it counts as a headway conflict; Default uses Sim Headway Seconds
Impact analysis	costs 2× compute and runs the network twice, then reports only the conflicts your schedule introduces — pre-existing network problems are hidden

Simulations are rate-limited per player (Sim Cooldown Seconds), capped globally (Sim Max Concurrent) and time-boxed (Sim Max Wall Seconds); a run that hits the time box is marked partial. Runs happen on a worker thread, so the server keeps ticking; if you close the window, a chat message tells you when the result is ready.

Reading the results

Your train — the stops the phantom reached, with simulated arrival and departure times, and its state at the end of the window (driving, waiting at a station, preparing to depart, parked, obstacle).

Other trains — the same, for everything else on the network.

Not simulated — trains that were excluded, and why: position could not be mapped onto the network, derailed, no schedule (manual train), schedule completed, schedule paused. An excluded train still sits on the track: it is treated as a stationary obstacle.

Notes — anything the simulator had to assume or could not model, e.g. an unsupported instruction, an unpredictable wait condition, "request stops are assumed to always be requested", "station-loaded checks assume the chunk is loaded", or "anchored to live snapshot — depends on current network state".

Conflicts — four kinds:

Kind	Raised when
Signal wait (section)	a train waits at a red signal longer than Sim Wait Conflict Seconds
Deadlock	a cycle in the wait-for graph (Tarjan SCC) — trains waiting on each other forever
Headway	two trains pass through the same section closer together than the headway threshold
Platform	two trains want the same platform at the same time

Each conflict carries its time window, the trains involved, a position, and a flag when it is non-deterministic (i.e. it depends on the current live network state rather than on your schedule).

Root causes — the useful part. Every signal wait at the end of the run is walked back through first-holder links until it reaches a train that is not waiting for anyone, and that train is named and classified:

Classification	Meaning
no station matches "X"	the schedule names a station that does not exist (* is the only wildcard)
no route to "X"	no path — check one-way signals and reversing room
finished its schedule and parked on the track	it is done and now it is scenery
standing on the track without a schedule	a manual train left in the way
held at X by its schedule	a wait condition that will not clear
deadlocked with …	it is in a deadlock cycle itself
stopped at a signal	cause could not be narrowed further

Each root cause lists how many trains are stuck behind it and since when. Fixing the root cause usually removes a whole page of conflicts.

Diagram and map

From the results window:

• Diagram — a time–distance diagram over the phantom's route corridor. Green is your train, diamonds are conflicts. Drag to pan, scroll to zoom, hover a line for details. Trains whose CRN category matches Sim Diagram Hidden Categories are left out.
• Map — the network map with conflict badges on the sections where they happened.

Debug export

With Sim Debug Export on, every simulation also writes a self-contained HTML playback viewer to dispatcher-sim-debug.html in the server (or save) directory. It is a debugging tool — leave it off in normal use.