Transport Fever 2 has no out-of-bounds traffic like some similar sandbox games like Cities Skylines have it.

That being said, through the use of mods and out-of-the-way lines and stations, you can simulate and tweak out-of-bounds traffic, to simulate interregional/intercity/national/international traffic.

This entails the use of stations and magnet or assets that generate traffic in an empty space on the very edges of the map.

https://gtm.steamproxy.vip/sharedfiles/filedetails/?id=2859046892

All vehicular traffic can be simulated.

Specifics will depend on different variables like how you want to simulate the traffic, vehicles used, etc. However, the basic setup is the same, and involves the use of a station on the edges if the map, with access to passenger or cargo generating assets. Best to use magnets, as they are small and can easily be customized and hidden away.

https://gtm.steamproxy.vip/sharedfiles/filedetails/?id=2249726960

https://gtm.steamproxy.vip/sharedfiles/filedetails/?id=1978047222
https://gtm.steamproxy.vip/sharedfiles/filedetails/?id=2250962410

You should start by building the station and a road that gives access to it:

https://gtm.steamproxy.vip/sharedfiles/filedetails/?id=2859047079

Proceed by building up a short stretch of road and then placing up magnets or another traffic generating asset or industry nearby.

https://gtm.steamproxy.vip/sharedfiles/filedetails/?id=2859047164
https://gtm.steamproxy.vip/sharedfiles/filedetails/?id=2859047186

Stations and airports can be quite bulky, but remember you can place around half of it out-of-bounds.

For maps with lots of water, you can set up ferry terminals and airports in a far away corner of the map where nothing other than water would exist otherwise, like this airport in the bottom middle part of the screenshot:

https://gtm.steamproxy.vip/sharedfiles/filedetails/?id=2859046933

For real-life recreations, I would try to set up stations generating the vehicles from and to the intended direction of travel - i.e. for this Japanese-themed map, the middle airport represents international traffic from China, towards Kansai airport, where approaches usually are from the south, so the placement of this airport makes sense.

For road and rail networks, if required, you can build the roads and rails outside of the map, as long as you connect them with two points that are within the map boundaries. This can allow for better connections for towns and stations that are located right at the edges of the map.

https://gtm.steamproxy.vip/sharedfiles/filedetails/?id=2859047103

For example, in the screenshot below, the main city station in this screenshot, Utsunomiya Station on the Tohoku Shinkansen line, is too close to the edge to set up an aesthetically pleasing "direct" connection, plus, I wanted to set up express trains that pass at speed here. Therefore, a longer and smoother path is desired.

https://gtm.steamproxy.vip/sharedfiles/filedetails/?id=2859046892

For rails, you can use the AutoSig mod to automatically build signals outside of the map boundaries:

https://gtm.steamproxy.vip/sharedfiles/filedetails/?id=2138210967

This transit terminal should then be connected to other places on the map with lines, as usual.

The demand to be generated by magnets is entirely up to you. You can setup a low demand to simulate sparsely used lines - or for performance reasons - or a high demand, to simulate connections with large other metropolitan areas, states or countries out of bounds.

For passenger traffic, I do recommend using commercial or industrial demand, as maps often tend to have surplus residential demand.

Note that if you want to simulate private car traffic as well, that you need assets that have a direct street connection to it, otherwise, they will only generate pedestrian traffic that will only be interested in using your own transport lines. The passenger magnet mentioned does have the option to include a direct street connection, but the vast majority of assets with passenger demand do not.

You can see in the following screenshots the same magnet, one with street entrance, another without. The one without will only generate traffic once a line is setup to the train station nearby.

https://gtm.steamproxy.vip/sharedfiles/filedetails/?id=2859416303
https://gtm.steamproxy.vip/sharedfiles/filedetails/?id=2859416330

You can name the magnets and stations with names that identify their intended destination. For example, for the magnets servicing the high speed line in Utsunomiya, the magnets were called "Sendai" and "Morioka" - the larger and main centers serviced by the high speed line out of bounds.

While this example uses a real life counterpart for easier identification, you can certainly use whatever city, region, or identifier name of choice - i.e. domestic, international, out of bounds, etc. These magnets will appear in the destination list, so it is a good idea to name them, instead of leaving them with their default name - for example, "no name" in the case of the passenger magnets.

https://gtm.steamproxy.vip/sharedfiles/filedetails/?id=2859416177

You can set up as many connections you desire. Keep in mind, however, that much demand and many lines will do negatively impact your PC performance. Best to keep it to a few select lines.

If possible and required, you can spruce up the area around the station to hide it out of view. For example, with trees or other assets.

https://gtm.steamproxy.vip/sharedfiles/filedetails/?id=2859048027

I hope the guide was useful.

Comments and criticism welcome.

Work on the guide still in progress and should be finished up within a week of release.