The following highways are numbered 666:
Belgium The pilgrimage centre of Banneux in Belgium is located on the N666 road.
Canada Alberta Highway 666 Ontario Highway 666 (former)
Ireland R666
Italy Strada regionale 666 di Sora (formerly strada statale 666 di Sora)
Netherlands Provinciale weg 666 NL Wiki Page
Philippines N666 highway (Philippines)
Sweden Länsväg 666, in Uppland, eastbound from Alunda. Z 666 Wiki SV
United Kingdom A666 road
United States U.S. Route 666 (former, renumbered in 2003 to US 191 and US 491) Florida State Road 666 Maryland Route 666 (former) Ohio State Route 666 Pennsylvania Route 666 Puerto Rico Highway 666 Farm to Market Road 666