Omsi 2 is a game with a game engine that can be side loaded by adding -editor in the steam launcher settings this will allow you to open any map or make your own map and edit it there are a lot of 3rd party free maps , buses and assets you can use in your own map the editor comes everything form setting up timetables , cars with there ai routes the ability to control if a road is one way 20mph or 100mph you start with a tile that is a 2d plane that you can edit the high of this 2plane such as adding a hill or a river the engine works in a 2D and 3D setting where all assets are mainly 3D with each face being its own plane while this sounds like adding a bus stop would mean making it in engine with all faces no you can add the full 3d model in the draw backs are that it will look a bit funny as its rendering it with your CPU (this game does not care for the GPU and the more powerful your CPU is the better the game play will be subject to other factors ) 

It is very clear as of right now, with my skill set I am nowhere close to being able to make AAA game however i am able to make a envoirmaent such as a road like you might see in omsi 2 now i had planned to make this in omsi but im not sure how i might do this i have planned on taking a map made with Ai and remove the road and remake a road with my own assets so that the AI will still work in testing and i can add better made houses shop bus stops etc however due the fact omsi 2 will only use a max of 4gb of ram what can be doen in detial is very limted however i am looking into this and how i can overcdome this i can also take a smaller map and edit this one as where the game can laod tiles into memeroy.

i have also considered making this for Roblox and having this as an open world that any can join, explore and review and add feedback - see [add page name and link]