I'd just like to get this out before I go on: I can't make addons, so don't say stuff like "go make it yourself" or something. Anyways, there have been topics on this before, but a train addon should be made. I was thinking for a passenger train someone could make a shorter, more blocko version of an EMD P42 locomotive.
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Maybe some matching cars could be made too.
For a freight train maybe we could use an EMD F7A. This is an old locomotive, as they were used in the 50's, and 60's. I'm sure you've seen one of these or a similar loco.
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And of course if you have trains, you need tracks, so let's get to that. For the tracks, it should be a brick, kind of like a road brick, except not so sharp turns. Maybe for a train spawn, it could be a track brick but have a spawn on it. Possibly someone could make the trains with the script like GSF Ghost's aircraft carrier no-mount script.
Anyways those are my ideas for a train addon. Feel free to discuss this and give ideas. I will check back on this topic regularly to check on posts and maybe some with good ideas will be put in the main post.