The following highways are numbered 166:

• Prince Edward Island Route 166

• National Highway 166 (India)

• Japan National Route 166

• A166 road

• U.S. Route 166
• Alabama State Route 166
• Arizona State Route 166 (former)
• California State Route 166
• Connecticut Route 166
• Florida State Road 166
• Georgia State Route 166
• Illinois Route 166
• Indiana State Road 166
• Kentucky Route 166
• Maine State Route 166
  • Maine State Route 166A
• Maryland Route 166
• M-166 (Michigan highway)
• Nevada State Route 166 (former)
• New Jersey Route 166
• New Mexico State Road 166
• New York State Route 166
• Ohio State Route 166
• Oklahoma State Highway 166
• Pennsylvania Route 166
• Tennessee State Route 166
• Texas State Highway 166
  • Texas State Highway Loop 166
• Utah State Route 166 (former)
• Virginia State Route 166
• Washington State Route 166
• Wisconsin Highway 166 (former)

Territories

• Puerto Rico Highway 166