OGF:Making realistic railways
As written in Tips for making countries that look realistic for the streets, that are for the railways important in same sense. To each little village leads a street - my be not a main-road, but then a smaller street. And so til the last house in the lonelity.
But the net of railways is more in the style as the net of the motorways and serve only important places (towns, harbours, touristic significant places, beaches, quarrys, mines) - with the important difference, that this medium of transportation in reality was build first.
In the heart of the city
Railways in most cases go into the heart of the cities, because towns were smaller 1840 til 1860 than today, so there was place for the railway or the needed place could be easily taken. In fact, it was the time when the old city fortifications were considered useless and demolished. This was a great opportunity to create space for the new iron horses and was a common concept. There are plenty of examples for this, i'll just list the german cities of Hamburg, Hanover, Bremen, Mannheim or Halle (Saale). Greater cities may have - til today - more than one station, where the rails finished. Often, the country's railroad construction started from these cities and there was a competition between several local railroad companies who all built their own stations, before they were united in the national railway company. You can see this still today in London and Paris, for example.
Around these stations in the city is the focus of traffic, there are densed retail-, commerce- and office-buildings. But not only this. Ending trains must stored, locomotives (in first time ever with steam-power) need maintenance and service so that in short way from the station these facilities must take her place. This place is normally much greater as the station itself. And if a station may be long up to 300m or 400 m (or longer), this service-area can be til kilometers. Often this areas are situated between two branches of railways. Often no roads go over this railway area, so that this piece of land is like an island in the street-grid of the town. I tag these areas as (landuse = railway) and it is rendered like the industrial areas.
'Gauge' means the distance between the two rails. It is measured in millimeters from the inside of one rail to another. The most common gauge is 1435mm, which is called 'standard gauge'. This is based on the 4' and 8 1/2" (english) spur of Stephenson and offers a good compromise between the amount of space the rails will take up, the curve radius possible, and the size of the trains.
Many instances exist of rails set wider or narrower than this. These are terms 'broad gauge' and 'narrow gauge' respectively and can be anything from 600mm to 3 meters. Narrow gauge offers the advantage of allowing tighter curves and cheaper construction, but the trains cannot go as fast or be as heavy. Broad gauge allows more space on the trains, but uses more room and the curves cannot be as tight.
The most common alternative gauges are 1668mm spanish or 1524mm russian Gauge and 1000mm Cape Gauge. The selection will depend on historical factors and the gradient of terrain to be covered.
A break of gauge is where one gauge meets another. There are several options available to railway builders to solve the problem of trains crossing this divide. The simplest is for the lines to terminate at this place and the passengers have to change trains. In some places the railway wagons have their bogies (the structures holding the wheels) changed to sets matching the new gauge. The most sophisticated system is to have bogies that can expand and contract the axles' width when going over a special machine in the track. The train must slow down, but does not have to stop so this is the quickest solution. Dual gauge track is another alternative.
Loading gauge is related to track gauge. It refers to the maximum allowable width of railway vehicles so that they will fit into tunnels and between structures beside the track. Loading gauge is not always matched to a particular track gauge: in the UK the loading gauge is hardly wider than the track width, whilst in Germany it is much bigger, even though these two countries both use standard gauge.
Diameter of curves
The railway between Hamburg and Hanover in Germany - opened 1847 - has since this time no lesser radius as 700 m on the open track, because it is flat land. If you design a modern hi-speed-railway, then on open track a radius of 5 or 7 km is useful. In the mountains this radius is lesser - but the the speed of the trains too. Lesser than 400 m is not realistic. So smooth the curves of your lines.
Absolute minimum of curves (may be in goodyards and to harbour-quais) by railways for slow moving units is 190 m. It is not usual (and possible) for railway-wagons to go to curves with lesser radius.
Only for metro-lines are curves with smaller radius down to 70 m usual and possible (see this adventural part of a metro-line on a viaduct from 1912 [] in Hamburg /Germany). But only in the case, that there is no more place in the heart of your city. Normally metro-lines too have a greater radius in the curves.
Trains cannot climb hills as steep as cars and trucks can, unless they are a specialised type of railway with a cog-wheel system to grip the track. A gradient of 1 in 20 (1 meter elevation for every 20 meters forward) is considered severe, and most railway builders will plan the route to avoid all but the smallest rises and falls. In the old days of steam trains climbing a hill required a huge amount of skill from the driver and fireman to avoid damaging the locomotive or running away on the downhill side.
Where it is impossible or impractical to avoid a steep climb, a tunnel will be dug. This is expensive but will save many miles on the route. A cutting will often be found at either end of the tunnel as the land rises but the railway stays on the level.
To cross a steep drop or a water body, of course, bridges have to be built. In very hilly areas, ingenious constructions such as spiral loops and switchbacks have to be used.
Electric trains have two possible sources of power: Overhead lines and third rail. Overhead lines can be used for the fastest trains, up to 400kph. They are safer and allow higher speeds, but are more expensive and can be considered visual pollution. Trains collect the electric power via a bow-shaped frame on the roof called a pantograph, which is spring-loaded to maintain contact with the wire and folds away when not in use. Third rail systems are typically used for speeds up to 100mph/160kph and are cheaper to build and maintain. However they are more dangerous in the event of people being on the tracks, and can be put out of use by icing and snow. Trains have a collector mounted next to the wheels of one car which draws power from the lines.
Diesel trains are used where it is not economical to electrify the lines. They can go anywhere, but have to be refueled and are more polluting and noisier. They are also not able to reach the top speeds of electric trains (fastest diesel train is the UK IC125 which can reach 125mph/200kph in regular service.)
Steam trains were once the only source of power, burning either coal, oil or wood. They were powerful and very reliable once the design was perfected, often being on service for seventy or more years, but had the disadvantages of being very polluting, needing to be refueled with fuel and water regularly, having slow acceleration, needing a lot of time to start up and shut down, and needing a crew of at least two. The fact that the driver had to see ahead from behind a long boiler was also a disadvantage, as was the fact that different locomotives with different wheel arrangements were required for freight and passenger trains of different lengths. Today steam is almost only used on tourist railways (which attract a big following) and in the poorest areas.
Number of tracks
Motorways many of us draw with two parallel items of blue lines, one for each direction, with a small space between. Railway lines are since the beginning only 24 to 28 feet broad (roundabout 8 til 9 m) for two tracks (of 1,43 m spur). So a line with two tracks in most cases are only one "railway" - line. Only if your railway have a broader spur as in Spain or Russia, you can calculate a little bit more for two tracks.
Most of us make no difference to a line with only one track, because the railway line general is small. But at your main-lines with added tracks for suburbian transportation or a parallel hi-speed line (or both) you should draw one parallel line for track 3, 5 or 7 and so on. The space between can be small - "10 m" are enought. This lines look on the map significant broader as a single drawn railway-line and so a your main-line with different sorts of railway-traffic looks more realistic at the map.
A lot of more work at all is to draw each single track. You can see this in Villa Constitucion (Ardisphere) or in Latina (Cidudad) in Latina. It looks really better and this is the standard in real OpenStreetMap in many great cities (p.e. Paris / France).
The tag for node of the station is set immediatly on the railway-line. This means only general a station, nothing over more tracks and nothing over platforms. If you will be here exactly, you can draw this items like in OpenStreetMap (see here [] the main-station of Hamburg / Germany with all single tracks and platforms now til 800m for two trains one after the other at one platform). But as compromise you can set one line of railway-tracks for the two tracks at a platform. But make them not to short - 300 or 400 m is useful. Too at smaller village today stops trains, who are 250 m or more. Sidetracks for overtaking slow moving freight-trains are 700 m or more (since 1900 !).
Junction your lines
If your city has two or more stations, please juctioned the lines. This times long are gone, that each company works only for itself. At the crossing of lines often is a curve, that allow the traffic to go from one line to the other. If this curves with a diameter p.e. 500 m snips up a piece of land, there then often are some allotments (landuse = allotments) for gardening use or one or two placees for football (100 * 70 m).
bridge and level-crossing
If one line goe over the other, then set a bridge. Snip the way at both side of the bridge and set there to the railway-tag the tags (bridge = yes) and (level = 1). The level must be 1 higher as the line, over which goes the bridge. Take care, that main-railways have a soft ascent of not more as 30 promille (means 30 m rise on 1 km track). So from the fork of tracks to the bridge you need nearly 350 m if one track holds his level or 200 m, if one track goes half down and the other half up.
In modern times level-crossings are avoided. But for siding-tracks to an industry-area they may have survived as here []. At the crossing point you set only the tag (railway = level_crossing).
Forks and crossings at metro-lines
Here [] is shown the crossing of two metro-lines, in this example both running over the earth. In this situation normally for better service run the tracks for the same direction at the same platform. You see, that you then need a minimum of 150 m til the bridge, where the one track of line A goes over the track of line B north of the station "Kellinghusenstraße". In a tunnel it is the same. So it is not possible, to set a branch-line with rectangeled curves - you need same room for the forking of lines.
If there is not the room enought for forking, the platforms of each directions can be at differnet levels (most configuration is level - 1 = downton, because in the morning is lesser time to get to work and level - 2 for uptown). An example see at Reaumur Junction / Cordoba, Latina, where the southern downton platform is on level -1 and the northern uptown platform is on level -2 18, -13.62273, 37.19269.
At forking stations the station can have 4 tracks, for each direction two tracks at each side of a platform. If you prefere the cheaper solution with only three tracks, the platform for the direction from outside the forking have the two tracks and from inside the forkings only one. Why? So the trains from outside can wait at the platform and not in the tunnel.
Do not forget the place for the service for your metro-cars. For the depots of metro-lines you need place - as here []. Minimum lenght of the depot-halls should be 120 m, better 150 m. In this example there are 12 tracks in the halls, at left side at station "Saarlandstraße" too and this town (Hamburg / Germany) has a third depot of the same importance and some little placings for store the trains - and that only for a net of 4 lines. So plan at a generous manner and give your metro-net a good service. Normally this depots are at the outside end of the lines (at morning for the workers in the city, at evening back from work or pleasure).
At the station of "Barmbek" you see the reality in towns: from north to the south one track for goods-transportation by railway, two tracks of commuter-railway and four tracks of metro-lines (two for each direction at same platform). The platform itself are 150 m long, not too much for a modern metro-service (only in the beginning of the building of metros til 1920 platforms are only rondabout 70 or 80 meters).
To show your metro-line in the OGF-wiki, you can set the line into a relation. All tracks of one line are to bound into one relation. But not the tracks of other lines. Each line is to bound in an individual relation. Tracks, where run two or more lines are bound in two or more relations. First work for this is, to take the scissor-tool and make pieces of tracks, where using of lines is changing. That means, you create a new relation with (type = route), (route = railway or subway) and (name = line-number or town-name and line-number) and (ref = shortcut of town and line-number).
If you set at the OGF-wiki a link like "opengeofiction.net/relation/number of the relation" then your line you can be shown in the OGF-wiki as an orange line at the map. As example this is realisized at the metro of Khaiwoon - please see 
Questions or comments? Things you would add or subtract? Feel free to share your thoughts on the Discussion page.
More information: https://wiki.openstreetmap.org/wiki/Tag:route%3Dtrain