system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: How are freight trains put together, and how long does it typically take?
gpt
Trains are usually organized in blocks, the yard crews usually switch out these blocks and place the blocks in order ahead of time.  For example: If you have to make a set off somewhere along the journey, that section of train is usually placed at the head end.  As for doubling the train over once its set in the yard, it can take anywhere from 30 minutes to an hour depending on the conditions.