CREATE TABLE table_1817879_2 (line_s_ VARCHAR2, segment_description VARCHAR2)

How many lines have the segment description of red line mos-2 west?
SELECT line_s_ FROM table_1817879_2 WHERE segment_description = "Red Line MOS-2 West"
SELECT "line_s_" FROM "table_1817879_2" WHERE "Red Line MOS-2 West" = "segment_description"