GWR Route: Banbury to Wolverhampton

GWR Route: North Warwickshire Line

Birmingham Snow Hill Station: gwrbsh1131a

In this photograph the weighted fouling bars adjacent to Platform No1 can be seen. When a train or even an individual locomotive, coach or wagon depressed one or more sections of bars, the Signalmen received an indication that a train was standing on this section of track and at the same time lock up all the incoming signals for that section of track (except the calling on signals). The fouling bars are wieghted to allow graviety to return them to their normal position. The extreme ends of the fouling bars are bent down to form a ramp in order to reduce the shock when the wheel flange depresses the bar. These particular weighted fouling bars at Snow Hill are adjacent to Platform No1 and were part of section ‘B’ which consisted of over thirty separate weighted fouling bars.

These weighted fouling bars were installed in large numbers at Snow Hill in November 1912 at a cost of £4,150. It is believed that the Great Western Railway preferred this mechanical detection method to electrical Track Circuit detection, because Snow Hill was at the top of two inclines, where sand was regularly used to improve traction and wet sand could cause an electrical short. The fouling bars were not immune to failure. These failures were typically caused by interference by a build up of ballast and sand preventing the depression of the bar, breakage of worn bars, or defective or broken electrical conductors. The weighted fouling bars necessitated extensive maintenance with bars being regularly replaced in the damp tunnel sections after only three years service. In 1921, the cost of replacing the tunnel fouling bars was £512. Nine reported failures of fouling bars occurred in the year following April 1924.

A sum of £410 was authorised in December 1913 for provision of electrical track circuiting and work commenced in 1915. As an additional safety precaution track circuits were added to the tunnel lines in July 1924 and special instructions were included in the regional sectional appendix in incase of failure (see time_table_instructions). From the start the track circuit failed more frequently than the fouling bars, although many of these failures were intermittent. It was found that the shoes of three fang bolts which passed through the longitudinal timbers and secured the inside rail, were touching the ironwork of the Park Street bridge , while on the outside rail a piece of lead packing was touching a rail fang bolt and a bridge girder. These faults resulted in intermittent failure of the insulation, which prematurely discharged the track circuit batteries. This particular fault was rectified by the removal of the lines over the bridge, installation of a layer of asphalt and reinstatement of the lines.

On 22nd May 1925 an accident occurred in the Snow Hill tunnel due to the failure of both the track circuit and the weighted fouling bar protection systems. Although the track circuit failure was only intermittent, the indication that there was a train on the line was ignored because of the previous frequent failures. As a result a light engine was allowed to proceed in to the tunnel where a suburban passenger train had stopped at a signal and although the light engine was travelling slowly, the smoky atmosphere made visibility difficult and a collision inevitable. Twenty two people were treated for shock or minor injuries. The Ministry of Transport report concluded ‘I suggest that the time has come to consider the question of substituting track circuit for the depression bars. The northern end of the tunnel is somewhat damp, and I understand that sand is used particularly when shunting back into the station up the gradient from the up line. If properly maintained, however, serious trouble in this respect need not, I think, be anticipated, and there would be no question as to the economy to be effected by this change.’

Fourteen years later in 1939 three sections of track work controlled by the Birmingham South Signal Box still retained the weighted fouling bar detection system:
Section B – Down relief line adjacent to Platform No 1 (locks lever 83)
Section C - Up main line tunnel approach (locks levers 2, 4 & 8)
[Also activated three different lamp indicators, depending upon which weighted fouling bars in the section are depressed]
Section E – Down main through line (locks lever 95)
Section G – Down line adjacent to Platform No 5 (locks lever 88)

Robert Ferris

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