Eidan, Tokyo plan ID codes for subway lines, stations Yomiuri Shimbun / Sept 21
In an attempt to make using the subway system easier for foreign passengers, Teito Rapid Transit Authority (Eidan) and the Tokyo metropolitan government's Transportation Bureau will introduce in April a system that assigns subway lines and stations a letter-number code...
...under the new system as follows: "Take the A line from A18 to A11, change to the H line at H9 and get off at H5."
Such directions currently would be given as: "Take the Asakusa Line at Asakusa Station to Higashi-Ginza Station, change to the Hibiya Line, and get off at Kamiyacho Station."