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Simutrans Extended => Simutrans Extended Development => Topic started by: Freahk on July 09, 2020, 03:08:54 PM

Title: Light rail speed limit thoughts
Post by: Freahk on July 09, 2020, 03:08:54 PM
Currently, trams do not have any drive by sight speed in any case.
From a German real-world standpoint, this is not correct, and I do not think light rails in Britain are allowed to move at 100 km/h without any signalling.

As I do not have this law book at home, I just asked the transportfever community and got the following:

Acording to BOStrab:
Quote
§49 Abs. 2:
Auf Sicht dürfen nicht fahren
1. Züge unabhängiger Bahnen,
2. Züge straßenabhängiger Bahnen
a) bei Streckenhöchstgeschwindigkeit über 70 km/h,
b) in Tunneln.

That means:
Railway vehicles that are independant of other systems are not at all allowed to drive by sight. (That's for example DLR, heavy rail and so on)
Railway vehicles that are dependant on road traffic, may drive by sight up to 70 km/h*, but are not allowed to drive by sight in tunnels.

*This is simply the maximum permitted drive by sight speed, it does not mean that road bound tracks are allowed to be used at this speed.

Further, some expections are stated in §49 Abs. 3, I won't quite these here as it's not quite relevant to the game anyway.
In special cases, which are 1. shunting movements, 2. short tunnels on road-bound tracks when there is enought sighting distance and 3. in case of disorders, attending operational instructions.


What does this mean for the game?
Determinng if a system is independant of other systems is quite complicated, so I'd just drop that point and use the tram vehicle type as a proxy for this.
This shouldn't be a huge problem.

100 km/h drive by sight feels just as unrealistic as fast drive by sight in tunnels.
Could we, adjust light rails maximum speed at drive by sight to 70 km/h and even less, say 35 km/h in railway tunnels?

It should be a rather small change with huge impact to realism.
Title: Re: Light rail speed limit thoughts
Post by: Vladki on July 09, 2020, 04:28:36 PM
Yes I'm in for 2 limits, preferably both configurable in simuconf.tab. Czech tramways seem to be limited to 60 km/h in drive by sight.
Regarding tunnels - wouldn't it be better to reduce the sighting distance in tunnels and thus also limit the drive by sight speed.
It may be that the braking distance from top speed is longer than sighting distance, and that should reduce the drive by sight speed.

Edit - tried it with vossloh tram-train. It goes full speed (100 km/h) in drive by sight on straight track, but slows down to 40-50 km/h at corners or slopes. It can brake in 327 m (2-3 tiles), So the tunnel sighting distance would have to be reduced to 1 tile to affect them somehow. But we have to distinguish sighting distance of signal (color light) and of obstacles on track...

However the rules about tunnel probably apply only to germany. There is a tram tunnel in Bratislava, and I did not find any signalling at the tunnel entry, so I think trams drive by sight and at full speed. The tunnel is illuminated. https://de.wikipedia.org/wiki/Burgbergtunnel_(Bratislava)
Title: Re: Light rail speed limit thoughts
Post by: Freahk on July 09, 2020, 04:43:09 PM
wouldn't it be better to reduce the sighting distance in tunnels and thus also limit the drive by sight speed.
Hmm...
Well at least in Germany, according to BOStrab drive by sight in such tunnels is generally not permitted, apart from very special cases like malfunctions, in which case very low speeds might be permitted on sight.
That was my thought about the 35 km/h limit. Players usually won't accept such low speeds, so they will install signals, but in case of "malfunctions" i.e. a manual reset of reservation, the vehicle won't stuck but can continue slowly.

About the sighting distance, it seems like a good option in the first place, but thinking about it technically, I am not that sure anymore.
Trams have a very hight acceleration, especially modern ones can reach 50 km/h on a single tile with ease, so even a sighting distance of 1 in tunnels might cause rather fast speeds there.
Fractals of tiles very likely won't work, because the "target point" system in reservations, that means the point where a vehicle will come to a standstill if it couldn't reservate further in the meantime, works purely tile-based. There is no concept of fractals.
The position, though does use fractals, so it would cause acceleration when enetring a new tile, then slowing down until reaching the end of the tile, where it will accelerate again.
I don't think this is desirable.