There is a three-way intersection on the border between Park Slope and Prospect Heights. It is at the corner where Flatbush Avenue crosses Plaza Street East/West, and where the Park Slope portion of St. Johns Place ends (before it picks back up on the other side of Grand Army Plaza).
This intersection is wildly unsafe. The traffic signal at St. Johns is largely unnoticed by drivers, who frequently pass through the stop line and stop in the crosswalk/intersection, with a small-but-still-significant number outright running the light. Pedestrians crossing both Flatbush Avenue at Plaza Street, as well as St. Johns at Flatbush, constantly dodge cars who drive aggressively.
A painted extended curb with temporary plastic bollard-like borders did little good; cars simply drove through them. Currently, there’s no curb extension of any sort there due to ongoing construction.
There is a constant stream of pedestrians crossing when the light is green on Plaza Street, with many little children, all of whom are at risk because drivers ignore that light.
Ideally, I’d like to see St. Johns Place closed to traffic for that final short stub between 8th Avenue and Flatbush/Plaza, but short of that I would like the crossing itself made safer.