Não informado. (2011). Railway Signaling. Simmons Boardman Publishing.
Παραπομπή σε μορφή Chicago (17η εκδ.)Não informado. Railway Signaling. Chicago, Ill: Simmons Boardman Publishing, 2011.
Παραπομπή σε μορφή MLA (8th εκδ.)Não informado. Railway Signaling. Simmons Boardman Publishing, 2011.
Πρόσοχή: Οι παραπομπές μπορεί να μην είναι 100% ακριβείς.