Possible Clues:

• Quartet of Monopoly properties: Abbr
• Norfolk Southern and others: Abbr
• They keep track records: Abbr
• Reading and Pennsylvania, e.g.: Abbr
• Four Monopoly properties (Abbr.)
• Monopoly board quartet (Abbr.)
• Basis of the game Ticket to Ride, for short
• Monopoly properties you can't put houses on, in brief
• $200 Monopoly properties, for short
• People-moving cos