Wouldn't putting the entire bicycle in be a problem?
I'm not sure if there are specifications for length, width, and height, but
if you remove the front and rear wheels and put them in a portable bag, there seems to be no reason you couldn't load it.
It becomes general cargo, not a bicycle.
In the case of KTX or subways, I understand that if you remove the wheels and package them, they are considered as cargo.
In the case of folding bicycles, even if you don't package them, they are considered cargo and can be boarded.
Express buses seem to treat it the same way.
