Blisworth Tunnel was the only section unfinished. This was despite the tunnel having been under construction for seven years: the gap was filled by a temporary horse-drawn tramway over the top of the hill, with goods being transported from boat to wagon and back again. The tramway, built in 1801, was Northamptonshire's first railway. In March 1805, the tunnel was finally opened and the rails were used to connect the main line of the canal to the River Nene until the branch canal to Northampton was constructed. Until the 1870s travel through the tunnel was only achieved by men lying on their
Southampton Tunnel partial construction of the Salisbury and Southampton Canal tunnel, which the railway tunnel crosses at an acute angle and slightly higher. Because the canal tunnel was lined with clay "puddle" it collects water which ends up in the rail tunnel making the latter very wet. In the 1960s an access was cut into the canal tunnel in order to examine it, although this was later sealed behind a new segmental wall structure when, between 1983 and 1985, the tunnel underwent extensive engineering works and the line through it was worked as a single line for long periods while remedial work