It's likely a usage-related calculation. If an intersection is known to nearly always have cars but rarely pedestrians, a walk signal makes sense. In Washingt

It's likely a usage-related calculation. If an intersection is known to nearly always have cars but rarely pedestrians, a walk signal makes sense. In Washington, DC, most intersections do not have a traffic button, so pedestrians and cars are equally accounted for in the signaling. Only a handful of intersections, where pedestrians are less likely, have traffic buttons.