Related Clues:

• N.Y.C.'s A, B, C or D
• Boston's Mass or Comm, e.g.
• Flight plan info
• 1 or 66, e.g.: Abbr.
• GPS calculation
• Constitution, for one: Abbr.
• Road map line: Abbr.
• 66, famously: Abbr.
• 'Hi, Claudius'
• "Hail! " to Caesar
• Road no.
• Park in NYC?
• Latin salutation
• Rural env. abbr.
• U.S. 1, for one