English Dictionary

As the new year dawned, Network Rail operated 562 SBs [signal boxes] of all shapes and sizes. The majority (473) are block posts, which carry out the primary role of signalling trains. … While most block posts often also control level crossings, crossing boxes are dedicated to crossing control. … Swing bridge boxes are an interesting category. Some, such as Trowse Swing Bridge in Norfolk, combine the role of block post with supervising level crossings and operating a swing bridge. … In common with crossing boxes, swing bridge boxes carry out their role under the supervision of a block post. For example, Keadby Canal SB needs to communicate with Scunthorpe PSB. When the resignalling of the Lowestoft line is completed, Reedham and Somerleyton Swing Bridges will no longer be block posts. … Records suggest that 100 years ago, there were around 12,000 block posts.