‘M’ for Metra System. A single color shared across all lines, with services delineated by number. Numbers increase radially from north to west to south, and downtown terminals concentrate a range of numbers.
                    For example, at Union Station you have access to 
                    M4North Central Service
, 
                    M5Milwaukee District North
, 
                    M6Milwaukee District West
, 
                    M7BNSF
, 
                    M8Heritage Corridor
, and 
                    M9SouthWest Service
.
                    At Ogilvie you would have access to 
                    M1Union Pacific North
, 
                    M2Union Pacific Northwest
, and
                    M3Union Pacific West
.