I want to take this moment to highlight an interesting and underappreciated junction reconfiguration success story: East 180th St.

Located at the junction of the Dyre Avenue and White Plains Road lines, and in between two yards, the area is among the more complex and delay prone in the system.

What was done to the area in the 2010s, though, was quite good (old = left, new = right). On the level of the physical plant, the rebuild eliminated all the area's slip switches, allowing for maintenance $$$ savings and higher reliability.

Perhaps more importantly, signal and track configuration modifications facilitated the elimination of a key AM-peak bottleneck.

To access the express track south of E180 St, express 5 trains long had to cross in front of local 2s north of the station.

While not an altogether *complex* merge, any delay here would ripple south on two of the system's most crowded corridors: the Broadway and Lexington Avenue expresses.

The issue was sufficiently severe that NYCT tried, in 2000, to flip the 2 and the 5 in the Bronx (so 2 => express and 5 => local), but the proposal was shot down by community opposition.
https://www.flickr.com/photos/127872292@N06/48536396152/in/album-72157710307680261/https://www.nytimes.com/2000/09/25/nyregion/plan-to-shift-no-5-train-is-abandoned.html

While not a complete fix, the reconfigured junction has allowed an interesting workaround for the merge: signaling improvements and track changes to deconflict yard movements now allow 2 trains to (slowly) run around the 5 via yard leads in the AM peak, eliminating the bottleneck

The new configuration is far from perfect -- in the PM rush, 2 and 5 trains still must cross in front of each other, causing delays, and movements around the area's yards before the PM peak cause significant midday delays in 2 and 5 service -- but...

...I find this story of value engineering and creative track utilization to be an interesting/instructive one for service improvement in a constrained environment and on a low budget.