Little Timmy want's to visit his friend Mike. But Mike lives in another city, and little Timmy is too young to drive! So Timmy needs to use public transportation. So what does Timmy do? Why, first he asks Mike for the busstop closest to his home. Then he walks down the street to the closest busstop to his home, and looks at the bus table. But - oh no! No bus stops at Mikes bus station! But Timmy does not give up. Like every kid nowaday he has a smartphone. He looks at all the names of bus stations busses from his station actually reach, and looks up if other busses pass the same station, and if there are some, he looks at all their plans to see if one of them stops at Mikes bus stop. Since there is still no connection, he repeats the process again, and again, and again. He looks up train timetables and thus even reaches faraway lands in his research, and since he looked up so so many plans, he finally finds a route to Mikes bus stop.
Obviously, Little Timmy is a Simuthanian, were it is common to plan trips like that. Start at your location and look up every place you can go from there, repeat for each of those places, until you reach your destination.
Now if I was Timmy, I'd do it differently. I'd start by looking for trains from the central station of my city to the central city of Mikes city, either direct or with one or two train switches, and not worry for the local part of the route. Only if I found a connection between the cities, I'd look up how to get to and from the train station. Or, if there is no city bus service, I'd ask my parents to drive me there (as little Timmy) - or walk there, or take a taxi, or hitchhike. I think the longer the trip, the further you'd be fine with using non-public transportation methods.
Back to the game - why would Timmy even want to visit Mike? Well, Timmy became randomly friends with Mike via a tinder-esk app that finds friends for you. It's called "locality_factor" and depending on the year you are in, the higher the chance to find a friend far away. There is no real reason why that app does that, other than that it has certain assumptions about reality.
In reality, public transportation became more widespread, faster and cheaper, thus more accessible over the years. The better the public transportation network, the easier it is to reach faraway places, and the more likely it is someone actually goes there. However, time is not directly a deciding factor here, only the network is. Time only decides how good the network can be, since it's quite hard to establish high-speed-connections on horseback.
Now, it's just a game, and not everything is possible. But I think at least Timmies journey could look a bit different just by adding some layers to the network. To do so, let's introduce an extension building for stations that converts that station to a higher level with access to another layer - let's call it L2. L2 Stations have an additional L2 coverage far bigger than normal coverage.
The L2 network is a subset of the normal network that only includes L2 stations and direct connections between L2 stations, not connections where a trainswitch at a normal station is required.*
Currently, any pax may desire to visit any pax-place on the entire map, restricted only by the locality factor. It's pretty much picking two random places and spawning a pax in each, destined to go to the others spawning location.
I propose to set a hard limit on how far a paxes desires can go. That is, spawn and destination are within a certain distance of each other, and no pax would just randomly decide to want to go to the other side of the map just like that.
Instead, a pax-pair will spawn at two different L2 stations, depending on the amount of pax in their L2 coverage, and will only route via the L2 network. If a route is found, 2 pax-pairs will spawn located at the two L2 stations and a 'random' location within the L2 coverage of that station.
This means you have 3 pax-pairs, covering the route from a "spawn" in one city to that cities central station, the route from that cities central station to another cities central station, and the route from that other cities central station to the "destination" in that other city.**
If the routing within one city fails, it does not influence the far trip anymore - that pax would have used a cab or other methods to reach the central station.
Now, does this even change gameplay?
Honestly, I don't think it would change too much. Players already build central stations, differentiate between small local lines and bigger main lines etc. - just the game does not and sometimes prefers local lines over mainlines. This would mostly be a tool for players to tell the game their intentions.
Yes, having L2 stations without any local busses or trams would allow to connect a whole city with just one station. However, one can already do that (changing the coverage radius or having each busstop as the same station) and with this, one can add in local networks later.
How about performance?
Might even improve. With the current system, pax may route across the entire map. The proposed system divides long trips in several shorter trips, which are easier to route. Especiallly the longest part of the trip, which only uses a restricted L2 network.
Besides, it's possible to reduce the max hops for pax drastically, even 2 might be enough to find a route within a city or within the L2 network, especially if players are aware of this and plan accordingly.
How about backwards compatibility?
Nothing gets removed, just new things introduced. By not setting a hard limit for local connections and not having L2 station extensions in the pakset, everything should remain as is.
Well, that's the idea for the moment. I'm not sure if I could get it across, but please discuss it
*) now, if L2 is a good idea, one could repeat the process for L3 or even L4.
**) That's definitelly possible, but it would be even better to combine the three routes into one, just so it isn't confusing why there are so many routes ending at the central stations.