I imagine it’s just the capacity of the street - for a 0.1 mile stretch of a 1-lane road, assuming 15 feet per car (including follow distance), 35 Google maps c

I imagine it’s just the capacity of the street - for a 0.1 mile stretch of a 1-lane road, assuming 15 feet per car (including follow distance), 35 Google maps clients is effectively a full street. If they all have destinations programmed, and are not moving, chances are something is blocking the road.