I frequent FaceBook and an add with a Lexus kept going through. Come to find out, its an add done by Lexus in the Unity SDK/Package. Unity has some very cool tutorials on YouTube. Looks to me, this is a place to begin. The realism is second to none... I couldnt believe it. But, Unity uses small scenes. So you would need to figure out how to do a world. Opening and closing cells? I dont know.
Hope that helps. Unity basic is freeware. Several package levels and most all you need is in package one, free base pack.
I had forgotten where this post was. Glad I found it. Ive been holding this information a few days now. Was so happy to learn about this. There is another 'system' besides Unity that is also quite popular for Indy game builders. I forget its name and I think I had downloaded it last year and never used it, deleted it. I downloaded this and will be checking it out. I need to get into a forum and see if it can do a simulator with a world base platform. At least entire countries or continents, rather.
Bill