The Test branch met the Itchen branch at the eastern end of the canal tunnel through the high ground to the West. The location of the junction was situated just to the south of the railway's later Southampton Tunnel on the eastern edge of what is now Palmerston Park. The Itchen branch curved to the north-east to reach a lock in the vicinity of the wharf which was downstream of Northam Bridge but construction of the Southampton and Dorchester Railway in 1846 and of a gasworks in 1848 destroyed much of the route. Excavations along this length in the 1960s failed to find any trace of it. Heading westwards from the junction, the incomplete tunnel alignment followed a straight line recorded on contemporary company plans as either or .