Signalling
JACKSON, Allen
Signalling and Signal Boxes Along the North British Railway, Great North of Scotland Railway and the CLC Routes
KAY, Peter & COE, Derek
Signalling Atlas and Signal Box Directory - Great Britain and Ireland
KING, Everett Edgar
Railway Signalling
Study of signalling mechanism and practices at the start of the twentieth century based on US railroads. Illustrated with diagrams and photographs throughout.
LANGLEY, P.A.
Level Crossing Protection
The Institution of Railway Signal Engineers Booklet No. 25