The following highways are numbered 166:
Canada Prince Edward Island Route 166
India National Highway 166 (India)
Japan Japan National Route 166
United Kingdom road
United States 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