[wongarsu]

It's still normal in many European cities.

The three obvious answers are crime, perception of crime (even though crime is going down, perception of crime is going up) and perception of the subway (is it a transport method for everyone or just for poor people and low-lifes).

Going one level deeper, you arrive at the media, poorly-handled immigration and failure in law-enforcement as main sources.

[scrappyjoe]

It is not clear to me how your ‘one level deeper’ reasons are connected to your ‘obvious answers’.

[noticing]

Exactly right, it’s normal. But it’s wrong to pin it on immigration. My 10-year-old daughter takes the Tube to Bethnal Green nearly every day, and it’s an incredibly diverse and culturally vibrant area.

[trilbyglens]

Yep. My boys (11 and 13) have been using public transport here in Prague by themselves since they were 9. It's hard to overstate how good it is for the development of kids to have that sort of trust and independence at such a young age.