Trains

For more mountainous or thick forest areas this is understandably. It required combustion engine trains, simply because of steep mountains, where it's difficult to put down power lines or forests with a lot of trees who can easily destroy power lines. USA however is mostly flat. Looking at some like Austria or Swiss, if I see this correctly, they also are on a good way. Here we have a lot of hybrid but in general our train transport is a mess of mixed.