Table of contents
- Why traffic congestion matters
- General Concepts
Traffic congestion and transport density/capacity can be controlled by different concepts and methods (general ones first, then the ones for certain way types).
Simutrans is a transportation simulator, so it won't show the same behaviour as the real world. Certain concepts are not possible, additional tasks may show up, but there are also things that would hardly be possible in reality.
Note: waypoints may not work well if placed on curves, diagonal track, crossings or bridges. Whenever a station/stop is placed on a tile that is already used as a waypoint, it will become a station/stop halt. Vice versa, a station halt becomes a waypoint when the station is removed.
The main use of hub stations is to join a larger number of low-volume lines with a few main lines. Example: local busses and trams connecting all parts of a city to an airport or a central train station.
Hub stations can be connected to each other by a back-bone, which can actually have any shape that is needed, like a ring or a star (then with a dominating hub in the center).
Trams: Unless you are ready to install detailed signal controls, it may be easier for you to build tram tracks in uni-directional rings (inside of a given city), which should meet each other at least at a hub station.
Other methods are:
- Prohibit slow road vehicles (even city cars and AI vehicles) to enter certain road sections, by guarding these with minimum speed signs.
- Divert slower trains to tracks or platforms parallel to the main ones, so they can be overtaken.
- With rail, electrify the routes used by the slowest trains, and make these electric. Then you can use the overhead cables to force these slower trains onto loop lines (slow running lines), so that express services can overtake on the non-electrified main lines.
- Instead of a single line with many vehicles, create more lines with different schedules, which meet at high-demand stations and hubs. This also allows you to adapt coverage and capacity to the actual needs, and to separate vehicles of different speed/acceleration.
- In some cases (e.&nbsp;g. if there´s only one scheduled halt where the vehicles are loaded, which applies mostly to freight, or if you can rely on a certain passenger generation rate), you can use load percentage at one stop (see also next paragraph) to avoid empty tours.
- In some cases (low-traffic roads, e.g. a line endpoint in the outskirts), the choose sign can be used (even on the way to a single-tile stop) to enforce a minimum distance between vehicles that pass it: it´s the distance between the choose sign and the stop.
- you can't delete them (you can switch to the AI player to make necessary changes)
- they can be set to a load percentage at a stop, thereby blocking all follow-up traffic
Road signals control through green and red light, that switch after some time the right-of-way.
Pressing the b key will show reserved track sections in red, which can help in diagnosing stuck trains. At the same time, the tool for repairing reservations is selected.
All kinds of signals are initially built as two-way. Clicking to build repeatedly on the same square makes the signal one-way in one direction, then one-way in the other direction, and then two-way again. A train will not proceed past a one-way signal against its direction of travel.
Simutrans uses Path Based Signaling (PBS), which means that a train is permitted to reserve a path and proceed along this path, if the reserved path does not use any tile of any reserved path of another train. This reservation procedure happens at any stop, which can be a scheduled station halt, waypoint, or signal. Therefore, stations and waypoints seem to act as if they had invisible signals.
- (Regular) signals
- These are easy to understand and use: a train waits here until it can reserve a path to its next stop.
- A train will wait at a pre-signal unless the block immediately adjacent to the presignal is empty and the signal at the far end of that block is green. In other words, a train in block A will wait at the pre-signal entry to block B until B is empty and the signal for entry to block C also shows green.
- Long-block signals
- These are used to allow single-track sections with several stations in one line, which can be passed in both directions. As reservations are allocated from one stop to the next one (see above), without looking ahead any further, sections like these would normally lead to deadlocks. Long-block signals support in avoiding these deadlocks: a train will only proceed if the entire track section up to the next signal is clear of existing reservations. (Note: the reservations are still done the normal way - from stop to stop.) In general, it is necessary to put long-block signals at all entry points of such a section, and trains/trams must not change directions in such a section (exceptions exist).
- Platform Choose signals
- A train at a platform-choose signal will choose a route to any free platform at its next station (in the schedule), and it will even try alternative routes to get there. If there is no free platform at that station, the train will wait. If the next scheduled stop is a waypoint, the train will proceed to the exact destination (x,y) point in the schedule, without trying an alternative route.
- "End-of-Choose" sign
- This creates a track signpost (and not, strictly speaking, a signal) that limits the scope of platform-choose signals. Specifically, a train will not choose a platform beyond an end-of-choose sign (exception: the exact platform that is defined in the schedule). NOTE: Do not place the end-of-choose signpost on the same tile as a signal (even if the program allows you to do so), because one of the two may be ignored.
On simple networks, when routes are set up, a waypoint should be set to prescribe whether the train should use the fast or slow loop in each direction, and rolling stock chosen to allow a corresponding running speed.
Alternatively, the longer loop may be electrified and the shorter not. Then either all "fast" or all "slow" trains can be provided with electric locomotives, which will use the loop to pass / be passed by steam-powered trains.
Aircraft are an expensive (per-vehicle) option for congestion control, though full loads of airplanes can very rapidly pay for their initial costs, depending on speed and number of passengers carried. Note that for aircraft to be effective for long-distance travel, airports must be well-connected to the city centres and attractions of a map.
If the airports are off on their own, without direct, fast linkages to the city center, it will be difficult to generate the numbers necessary to make the planes profitable.
In some games, it is possible that your rail service will still carry more passengers than the airplanes, so plan ahead to make sure sites for airports are as close as possible to the city center. Though a good high-speed rail line will be able to get closer to the city center more often than not, because airport infrastructure tends to be very land-extensive.
Originally written as http://en.wiki.simutrans.com/index.php/Traffic_congestion_control