The Stoup book is a good reference for this topic. In response to David's question, yes, there was a third (middle) track in service from Brown to Woodbury during the time when the tracks were still electrified. Stroup's book refers to this in the caption on page 100 as an express track, and the middle electrified track can be seen in the photo on page 102. The middle track was eventually taken out of service and torn up after electrification ended.
Actually, two manually accessed sidings were left remaining of the former middle --- a short one in Brooklawn and a little longer one about a mile south in Westville. Stroup's book in the page 100 caption mentions three portions retained, the third being the section of track extending from Brown tower to a point just south of Newton creek. However, this portion was not a "siding" per se --- it was part of Brown's controlled interlocking with switches controlled by the Brown operator and was in regular use as a running track for trains off the Millville main.
From the late 60's on cars were rarely if ever left on the Brooklawn or Westville sidings. The most frequent use of the Westville siding was by the the yard crew, based at Bulson St., that would daily work the business and industries (most notably Texaco) served by the Westville industrial track. The crew would come down from Bulson St. in the morning, and then back into the clear on the Westville track for their day's work. In the afternoon, they would shove out of the Westville track and utililize the middle siding to cross over to the northbound main to run with the grain back to Bulson St. You can see the crew doing this in the Stroup picture on page 103. (Incidentally, the picture caption mentions the yard job as being 23A, which it may have been in 1965 when the photo was taken. By 1969, the Westville work was performed by 22A. 23A handled the daily work on the Grenloch branch.)
My only guess as to why cars were left standing at Brooklawn, unattended, for periods of time during the 50s would be to ease congestion at Bulson St. It seems likely that cars for the Westville track or other businesses in the area could be stored at Brooklawn to open up more room at Bulson St, which was a small but very busy yard.
Hope this is helpful.
