A-line or A Line may refer to: Transport A (New York City Subway service), rapid transit line A Line (Los Angeles Metro), a light rail line in Los Angeles County, California A Line (RTD), commuter rail line between Denver and Aurora, Colorado Atlantic Coast Line Railroad, rail line in Florida A Line (Minnesota), a bus rapid transit line in Minneapolis, Saint Paul, and Roseville, Minnesota A-Line (Hamilton), planned rapid transit line in Hamilton, Ontario, Canada RapidRide A Line, bus route in King County, Washington Line A (Buenos Aires Underground), Argentina RER A, commuter rail line in Paris, France A (Los Angeles Railway), former streetcar service Other uses A-line (clothing), a style of skirt or dress Arterial line, a thin catheter inserted into an artery A-line - a finding in medical ultrasound of the lung See also A-A line Aline (disambiguation) Line A (disambiguation) Line (disambiguation)