Why don't all Route 13 trolleys go to Darby

Why don't all route 13 trolleys go to darby?

Currently, if you take a trolley west of Yeadon loop, you're pot comitted to a route to at least Island and Woodland. As such, only Route 13 trolleys pulling out of or into Elmwood Depot serve that section between Darby TC and Yeadon.

The turnback track that would allow a Route 13 trolley to travel west on 10th to Darby TC and back east on 9th toward Chester Ave was abandoned around the late 80s. It's on a private right-of-way for a short run so it isn't simply a matter of renewing a switch. Worth investigating restoring, but not as cut-and-dry as you may think. A switch at 9th and Main would be impossible due to geometry.

What would be the advantage of having two subway-surface routes running between Juniper Street and the Darby Loop? For most of those runs, Chester and Woodland Aves are not that far apart ( though on their outer ends they are). Is there really enough traffic on the western ends of each street to Darby to justify having both routes terminate there?

The 11 and 13 aren't far apart, but between 60th Street in SW Philly and 6th Street in Darby, they are on opposite sides of CSX, which is a relatively impermeable barrier, so they serve different markets. For passengers, the importance of the connections at Darby TC to the 113, 114, and 115 have only gone up, as job sprawl continues to be an issue. Also, consolidating the terminals of the 11 and 13 allows SEPTA to have more flexibility during disruptions to either line, and also lets SEPTA downgrade the amount it spends on upkeep of crew rest facilities at Yeadon Loop, which is currently a very necessary, and nontrivial, expense.