Possible Clues:

• Me.-to-Fla. route
• Me.-to-Fla. highway
• Rte. running from Key West, FL to Port Kent, ME
• East Coast rte
• Maine-to-Florida rte
• Auto route from Me. to Fla.
• Hwy. through six Eastern state capitals
• Florida-to-Maine hwy
• Primary rte.?
• In Key West it's known as the Overseas Hwy.