> Was there an eastward signal on the signal bridge east of 16th st for Mainline 3? If not, where was the next signal past the pot signal at the tower granting you authority to proceed eastward on Mainline 3?

In the photo, the signal on the bridge directly above the locomotives with the blades pointing to the left is for EB movements on ML 3. The corresponding signal for EB movements on #4 was a ground ground mounted mast, closer to the tower, and is hidden behind the locomotives (the tracks were numbered, from right to left: 1, 2, 3, and 4; 5 & 6 were the electric tracks further east). The short arm ("inside" the bridge) governed movements through a crossover between #3 and #4.

The next EB signal on #3 would be at 34th St, west of the power switches, because there were no switches on #3 between this location and 34th St. #12 will crossover to #4 at 34th St, where #4 becomes the EB main.

The short arm "inside" the bridge with the right facing blade, just to the right of the locomotives, is for westbound movements on 3 because there is a crossover from 3 to 2 about 1500' beyond the bridge. The middle signals are for ML 2, and the far right signals are for ML 1.