The Grange / Hendon lines in their time were quite busy.
When the line ran to Henley Beach there was a crossing loop at the golf course and at Albert Park. plus the yard at Henley Beach.
With the branch and yard at Hendon there was a possibility of several trains being in the area.
During the second world war there was a lot of traffic both freight and passenger into the munitions works.
Soon after the introduction of Redhens in the 1950s there was a collision on Port Road crossing between an F hauled train and a redhen.
It appears to have been, that a staff was withdrawn simultaneously from both ends. ( Or the machines failed) So both trains met at full speed because they both had a staff.
The staff was used until Albert Park was straightlined about 1990 or so.
Right until the end of the short siding retained for track machines, it was possible for two trains to be on the line.
Associated with this short staff section would have been a block indicator with a red dumbell showing. The could be associated with a bell or buzzer to indicate that a staff was being withdrawn and the person was seeking clarification that the line was clear.
In the upper quadrant signal days this was when the twin arm signal next to Port Road would be set for up trains.
That signal was how I learnt about signals as I always hoped to see both arms vertical, but it could not happen, so I had to learn why.
When the new signalling system was installed the last fuel signal lamp in Adelaide was removed from Albert Park, and it takes pride of place in my train room so it is a cherished connection with the area.