Trunk 4 is part of the Canadian province of Nova Scotia's system of Trunk Highways. The route runs from Highway 104 exit 7 at Thomson Station to Glace Bay. Until the construction of the Trans-Canada Highway, Trunk 4 was a major traffic link in northern Nova Scotia and Cape Breton, and is still used on Cape Breton as an alternative to Highway 105. The highway was originally called the King's Highway, however, this name is no longer applied to the entire road. The only remaining historic section of the highway that maintains the name "King" is King's Road in Sydney.