Possible Clues:

• Union Pacific et al.: Abbr.
• Cos. with ampersands, often
• Monopoly 4some
• Rock Island and Reading: Abbr.
• Some Monopoly purchases: Abbr.
• B.&O. and Reading, e.g.: Abbr.
• Monopoly board quartet: Abbr.
• Some Xing crossers
• Monopoly foursome, for short
• Transp. lines