system
Given the following post, respond as if you're commenting on Reddit:
human
Eli5 My three year old boy wants to know why do trains whistle? And different times in there journey? We hear train whistles from our house.
gpt
They usually whistle when entering populated areas and go over level crossings. It’s an added security measure because many times trains are not very loud and can « sneak up » on you. The whistling makes it very clear they are coming.