OK, so I've resorted to actually looking it up: Toyosu has 4.2% cycling mode share, and Ariake has 2.1%. The figure for 23-ku as a whole is usually said to be around 13%, and the figures for other parts of Koto-ku seem compatible with that (e.g. 15% for Kameido). https://www.city.koto.lg.jp/650102/documents/030322boumachis... , page 15.