The section between Mahoneys Corner and Glenholme was originally part of Trunk 4 until the 1960s when it was designated Highway 104.

Trunk 4 is discontinuous between Exit 14A, Highway 102 in the west and Pictou Road in Bible Hill in the east.

Trunk 4 continues east of Kemptown on its original alignment through Mount Thom to Salt Springs.

From Salt Springs to Westville, the present alignment of Trunk 4 was used as Highway 104 from the 1960s until being bypassed in the 1990s.

Trunk 4 uses an old Highway 104 alignment between Barney's River Station and Marshy Hope.

East of Sydney it continues along Grand Lake Road to Reserve Mines and Glace Bay.

When controlled-access sections of Highway 104 were first built in the 1960s, the number replaced Trunk 4 entirely west of New Glasgow.