Heres the first bridge on the Colchester Fill. Both these pictures were taken shortly after abandonment. The second after the scrappers had done their job.
Signals on the drawbridges:
They had Distant signals located approximately one mile north and south of the Draws and then a home signal located 500 feet north and south of the draw.  They were interlocking, which means the signals would display as soon as the draw was opened.