>>1176842cont'd
The bridge railway opened in 1939, about two years after completion of the Bay Bridge. For a brief time, it was used by all three companies, and only by the Key System from 1941 onwards. A gianormous yard, the bridge yard, was built on the Oakland side.
Here's the thing with the bridge railway: All of the mentioned lines converged onto the double tracked bridge railway. This meant five Key system lines which each ran half-hourly during off-peak hours, plus the IER and SN. Adding to that deadhand movements to and from the bridge yard, it means a whole lot of trains. To cope with this, an ingenious signalling system was devised which would allow for much tighter headways than usual, the cab signalling system.
