This picture shows the crossing of Powell street with California street. At this point, the “California Street Line” and the “Powell Street Line” of the San Francisco cable car system cross each other.
The Powell Street cable passes underneath the California Street cable at the intersection of the two lines, because the California Street line was built first. Therefore, Powell Street cars must “let go” of the cable at a point marked on the pavement, coast across the intersection, and pick up the cable again on the other side. If the cable car has to make a stop after letting go of the cable, passengers have to get off and push the cable car back into position.
The crossing at Powell and California has a manned signal tower (as you can see on the right of the picture), because cable cars coming uphill from the south on Powell or from the east on California cannot see cross traffic until they are almost in the intersection.

Powell Street Crossing