Middle Track Operation on the N&W

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I am looking for information on exactly how the N&W operated its Middle Tracks. 


DEFINITION: A middle track was a track, located between two signaled main tracks, provided so that interior slow trains (freights) could get off the main track when they "fell back on the time of" a following superior train (e.g. a First Class train.) 

EXAMPLE of the Use of a Middle Track: Extra 2042 West, a tonnage train, leaves Elliston on the Westbound Main Line not far ahead of No. 25's time. Making a slow run up Christiansburg Mountain, the crew of Extra 2042 West pulls into the Arthur Middle Track and lets No. 25 proceed around them without delay. The crew of the Extra West does not have to be instructed by message or Train Order to do this -- the rule told them what to do. Rule 86: "Unless otherwise provided, an inferior train must clear the time of a superior train in the same direction not less than five (5) minutes; but must be in the clear at the time a first class train, in the same direction, is due to leave the next station in the rear where time is shown." (Over the years, there were all kinds of permutations on this rule, allowing Extra trains to run ahead of Third and Fourth Class trains, and the like, without clearing. But those permutations are not germane for the question I'm raising.) 

QUESTION: My question is this... What provision did the N&W make to prevent opposing trains from entering the same middle track at the same time, and coming to a nose-to-nose Mexican Standoff? 

ONE OBVIOUS SOLUTION is to provide "middle crossovers" (escape crossovers) somewhere along the middle track, and designate the east portion of the middle track for the use of westbound trains, and the west portion of the middle track for the use of eastward trains. This is what the N&W did on long middle tracks which had the capacity for holding two trains. 

ANOTHER SOLUTION would be to designate certain middle tracks as for the use of only eastbound (or only westbound) trains, "unless otherwise provided," which meant unless otherwise instructed by the Train Dispatcher. 

A THIRD SOLUTION, and the one I think the N&W used, was to provide some form of signal protection against opposing trains pulling into a middle track simultaneously. So that, if an eastbound had opened the switch to enter a middle track, the switch at the far end would be electrically locked and could not be used by a westbound for pulling into the same middle track. IT IS THIS THIRD SOLUTION that I am curious about... IS THIS WHAT THE N&W DID? HOW DID THE ARRANGEMENT WORK? 

Middle tracks generally went the way of the DoDo Bird with the advent of CTC, the reduction in passenger trains, and the era of "Stuart Saunders reductions." 

So, to REITERATE THE QUESTION, does anyone know how the N&W operated middle tracks NOT equipped with middle crossovers? 

Sorry for the longwinded question, but it asks about a situation which needs a rather full explanation. 

-- abram burnett