page twenty

The Junction

Every other room here gives you as long as you like. This one gives you a clock. Today's number lays out a station, writes a working timetable across it, and then hands you the panel: thirteen to seventeen trains are going to turn up at the edges of that diagram whether you are ready or not, and each one needs a road to come into and a road to leave by. You cannot crash anything — the interlocking will simply refuse you — so the only thing you can lose here is time, and it is measured.

Click a train to take it, then click the road you want it in. Click it again — or use the button — to let it out. Trains waiting outside are the little tabs at the edges.

Station — Clock — Away — Lost — Right time — Panel lost —
Speed
Express Stopping service Freight Parcels Empty stock Road occupied Road set

Space starts and stops the clock, 1 to 9 put the train you have taken into that road, D or Enter sends it away, N deals another station and T comes back to today's.

What the panel will and will not let you do

  1. 01

    A route, not a set of points

    You do not throw individual points here, any more than a signalman does. You ask for a road from where a train is to where you want it, and the frame either sets the whole thing and clears the signal or tells you which bit of track is standing in the way and who is holding it. Every route is a list of sections — the line it comes in on, whichever slices of the throat it has to cross, and the road itself — and two routes that want the same section cannot both exist.

  2. 02

    The throat is the whole game

    Notice which line each road lies opposite. A train coming in on the line that points straight at platform 2 crosses nothing at all to get into platform 2, and crosses four slices of the throat to reach the loop at the bottom — blocking everything in between while it does. Putting a train in the nearest free road is usually right and occasionally the worst thing you can do, because the road you leave free is the one the next train cannot reach.

  3. 03

    Length, platforms and dead ends

    A road is only as useful as it is long: an eleven-coach express will not go into a nine-coach platform. Passengers need a platform, so a stopping service cannot be put in the goods loop — though a train booked non-stop does not care, which is the cheapest trick available to you. And the bay is a dead end facing west: only something that arrives from the west and goes back west can use it at all.

Where the number to beat comes from

Handing you a timetable at random and then scoring you on it is only fair if the page knows the timetable can be worked. So the station is dealt once and the timetable over it is dealt up to sixteen times, and every one of those drafts is put through the entire shift headlessly by a dispatcher that sets every route it legally can, as early as it can, preferring the road nearest the line the train is on and the shortest road the train will actually fit in. The draft that dispatcher got round with the least delay is the one you are given, and the delay it lost doing it is the number in the rack. Over three hundred stations it has never once failed to get every train away; the median shift costs it a little over three minutes, nine shifts in ten cost it under six, and the worst one seen cost it sixteen.

It is not a good signalman, though, and that is the point. It never holds a road back for something better, it never notices that the loop would do for a train that is not stopping, and it will cheerfully drop a six-coach parcels train into the only platform long enough for the express that is four minutes behind it. Beating it is a matter of thinking one train further ahead than it does. All of this costs about sixteen milliseconds, which is why you did not see it happen.

Two notes on the clock. A train that is refused a road does not vanish — it stands outside on its line accruing minutes, and nothing behind it on that line can move until it does, so one bad decision at the west end is felt at the east end six minutes later. And a route is released as a whole when the train completes it, not section by section as it passes, which is a real and deliberately old-fashioned way of working: it costs you a little capacity in exchange for never having to think about where the back of a train is.

The same date integer that draws the flow field on the front page lays out this station and writes its timetable, and it is doing nineteen other jobs besides — it grows the Garden, writes the Chimes, deals the Lattice, files the Almanac, scatters the Observatory, raises the Atlas, breeds the Menagerie, lights the Orrery, invents the Codex, runs the Chronicle, builds the Folly, cuts the gears of the Engine, threads the Loom, opens the Exchange, invents the rules of the Gambit, locks the doors of the Warren, arranges the corridor in the Inquest and cuts the gorge under the Span. Nothing here is saved between visits. Tomorrow this station is somewhere else, under a different name, with a different lot of trains on it.