Columbia subject headings:
Local transit--Illinois--Chicago Metropolitan Area.
Railroads--Illinois--Chicago--Commuting traffic.
Harvard subject headings:
Chicago Metropolitan Area (Ill.)--Transit systems.
Local transit--Illinois--Chicago Metropolitan Area.
Railroads--Illinois--Chicago--Commuting traffic.
Princeton subject headings:
Chicago Metropolitan Area (Ill.)--Transit systems.
Railroads--Illinois--Chicago--Commuting traffic.