In my last post about the mall, I mentioned how the intersections on the mall have secondary call loops, that is, call loops that are not located at a platform. Normally, operators don’t need to use these because the signals will be cascading from when the pre-empt at the platform was called. Secondary call loops are there to be used if the signal times out before the train gets to that intersection – they allow operators to quickly recall the signal to keep moving. That’s not the only way to get a pre-empt again - as I’ve mentioned before, some intersections are equipped with a push button, where an operator can reach out of the cab window and use the push button to recall the pre-empt.
However, not all pre-empted intersections have push buttons or secondary call loops. For example, on most of Burnside (which uses mass detectors instead of call loops) a train cannot get a permissive signal again if the pre-empt times out or fails to display a white vertical. Continuing through the intersection on a yellow horizontal is the equivalent of running a red light for a train – it’s a rule violation and it’s dangerous.
So if it should happen that a pre-empt times out or fails to change to a white vertical in the first place, and an operator has no secondary call loop or push button, there is a set standard operating procedure (SOP) to safely proceed through the intersection. If you’re listening to the radio and you hear an operator requesting permission to SOP the intersection, what they’re asking for is clearance to proceed on a yellow horizontal.
First, the operator has to stop the train before entering the intersection on a yellow horizontal. Next, they call Control for permission to SOP the intersection. If it is an intersection that can be safely SOPed*, Control will tell the operator to wait for a fresh parallel green and walk sign. Where applicable (e.g. on Burnside) the operator will also have to wait for a red left turn arrow.
*Not all intersections can be safely SOPed – here heading west into Goose Hollow, Collins Circle at 18th & Jefferson has a secondary call loop. However if an operator overshoots it, they will not be able to SOP the intersection
When the auto traffic lights have a parallel green and red left turn, the rail operator will sound horn warning and proceed when safe. This includes checking for emergency vehicles. As seen from 2005, an emergency vehicle’s Opticom can’t make a white vertical go back to a yellow horizontal, but if they placed their call before you it will prevent a white vertical from coming up at that intersection.