No smoke to worry about in the tunnel as there would have been a decade before! The original single track line seen here high on the left and running when laid in 1863 just to New Passage , on this side of the Severn , was too steeply graded for Bristol bound trains , and so the Great Western in 1886 laid this new eastbound line with its one in one hundred gradient from Pilning to Patchway upon the opening of the Severn Tunnel . Records relate to eastbound freights having to take an additional brakevan for the passage through the Severn Tunnel , same being enclosed , doubtless for the health and safety of the unfortunate guard , such additional vans being uncoupled by the banking engine upon arrival at Pilning with that engine and van's subsequent return through the tunnel for their next duty. I do not know when that practice ceased.David J Hayes comments,Same Class 8 traditional mixed wagonload goods service as per the 1672 Swindon picture. Possibly a Severn Tunnel Jn. to Temple Mills or Ripple Lane train? He adds Further information has come to light, which would pretty much confirm this as being a Severn Tunnel Junction (STJ) to Temple Mills traditional mixed wagonload service, which may well have also called elsewhere en route, such as Acton Yard. I believe as of summer 1974, it was due off STJ at 06:55.