The road starts at traffic lights on the A1306 near the Ford plant; the B178 is actually on a one-way loop here, with northbound and southbound traffic joining the A1306 at adjacent sets of lights either side of McDonald's. After the two directions meet the road heads north along the residential Ballards Road to reach a grassed expanse, Dagenham Old Park. The houses come back and then the two carriageways of the road split to reach the road's terminus at a surprisingly large roundabout on the A1112.
Dagenham in 1923
The original route of the B178 is quite different. That started on the A125 in South Hornchurch and followed what is now the A1112 as far as the A124 in Becontree Heath. The current route of the B178 was met in Dagenham East.
It seems that the B178 gained a spur in the 1950s, then the former mainline was renumbered A1112, leaving the spur as the only section of the B178.