If you're a daily commuter, you'd know these causes for delays quite well. Would you agree with my take on how often these delays happen?
Assuming we commute 5 days a week using BART:
2 out of 5 days we would run into delays caused by some type of 'medical emergency' (typically someone fainting due to lack of air and anxiety caused by overcrowding)
1 out of 5 days we would run into 'police activities' at a station
1 out of 7 days we would run into 'track problems'
If it's raining, then you'll run into 'track problems' 4 out of 5 days! Am I not right!?