I'll go with a combination of the first two points. Back in the late 70s/early 80s, when I was a young pup just getting to know my way around Cajon, there were few things more memorable than the descent of that one last train at dusk down the 3% of the South Track. Caboose markers disappearing into the orange haze, the smell of creosote that had been baking all day under the hot sun, and that distinct smell of heated, smoking brake shoes.