Kindly supply an example of prose using the term in a t/t context. If
it's short for "time slot", then it's a time during which a train can be
on a piece of track (ie, the line between stations, the track along
platform 1, etc.) It's obvious, I think, that two trains can't occupy
the same piece of track during the same (time-)slot.
IMO, you will find that the graphic method of t/t planning works best.
Time slots as you describe them are what I'm after. I would like to know how
they are used in planning timetables... Of particular concern to me is the
way the length of a time slot is calculated, and how each time slot for one
section of track connects up to time slots for ajoining sections of track.
Ian J.
{(Length of track/average speed of train) + safety factor} --> {timeslot
for that section of track}. Only one train can be on that section during
any one timeslot.
Eg, assume section is 5km, the average train speed is 50km/h through
that section, safety factor is 3 minutes, then the time slot is 15
minutes. That means you have to allow at least 15 minutes for any train
running over that track section. Calculate the timeslots for every
section of track on a given route, and that will be the minimum safe
time over the route. You can calculate time slots for fast and slow
trains, which is "merely" complication in planning the time table.
That's why timetables are usually constructed graphically.
A "track section" is bounded by signals: the signalman (or the
dispatcher at a central traffic control station) must know when each
train enters and leaves a section, and whether or not it is on time.
Each track at a station is also track section: the minimum time slot is
the time it takes to pick up and discharge passengers safely, usually
reckoned at 1 to 3 minutes for timetabling purposes. On a single track
line, trains have to cross at a station, so the minimum safe time is
lengthened, since there has to be a safety margin to allow the trains to
arrive from opposite directions, etc. Also, engine crew changes,
servicing of dining cars, pickup and drop off of parcel freight etc can
all affect the timeslot at a station. You can see that timeslots are not
necessarily fixed, which is, er, another complication of time table
planning.
Note that freight trains are also timetabled. They may be regular
freights with a daily schedule, or they may be given ad hoc timings to
fit them into the regular plan on that day.
For the graphic method, use a nice large sheet of 1/4" squared paper.
(Tape several sheets together if necessary.) Calculate the distance
between the stations, and write their names down the left hand side,
separated by s suitably scaled distance. Eg, 10km (2 squares) to the
half inch. Draw a horizontal line for each station. Mark hours from
00:00am to 24:00 (12 midnight) across the top at 1" to the hour, and
draw vertical lines. A diagonal line drawn from one station to the next
represents a train travelling between stations. The slope indicates both
the direction (up and down) and the speed of the train.
If the lines of two trains intersect between stations where is no double
track, then one or both lines will have to be adjusted so that the
trains cross at a station. In practice, the premier trains are
timetabled first, and the lesser ranked trains are fitted in between them.
I hope that's enough clues to get you going. Devising timetables can be
a hobby in itself, so be warned... :-)
HTH
Here's a url for a research report on timetables for public use. About
halfway down, there's an image of a graphic timetable, which should help
you see what I meant. You will see sloping lines on a grid, not a very
large image, but it should do.
http://www.communication.org.au/cria_publications/publication_id_91_439407953.html
Have fun!
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