Which major corridors have the most going on right now.

Answers broad questions like "what are the busiest routes", "where is
traffic worst", or "which highways should I avoid today" across all 17
tracked corridors. by="activity" ranks on live events (full closures
weigh most, then incidents, lane closures, chain controls);
by="congestion" ranks on measured speed vs free-flow at each
corridor's midpoint and needs the traffic feed to be configured -
if it is not, the ranking silently falls back to activity.

Each entry carries the counts and a one-line reason, so the answer
can say WHY a corridor ranks where it does, not just list names.