This was a double track tunnel which ran west under the Monkland Canal (now the M8) to Pinkston Road. About mid way there was an airshaft just to the north of the St Rollox [1st] depot.
Buchanan Street Tunnel West Signal Box was at the west end of the tunnel, where the lines opened out to serve Buchanan Street and Buchanan Street Goods. It closed with the line in 1966.
Buchanan Street Tunnel East Signal Box was at the east end and closed much earlier in 1887. The line ran through a cutting to St Rollox [2nd] station and on to the east to serve destinations north and south.
The Buchanan Street extension cut through the Pinkston Bog waste (from the St Rollox Chemical Works), requiring some effort to stabilise the tip. In 1856 the Buchanan Street Tunnel was flooded with material when the bog material shifted.