Beijing Subway - new lines missing

Dear guys,

there are a lot of details on Openstreetmap for the old Beijing subway lines, but some new parts and new lines are missing.
Since GPS is not working in a subway tunnel (suprise, suprise, …) I would like to ask if somebody have some sources to add the missing parts.

Otherwise if you have an idea how to collect the position data, just let me know.

Thank you!