There aren't that many SkyMarshalls, they can't and don't cover all flights. So you never know when someone going for his 72 virgins is going to be on your flight, or on your train, bus, or in your shopping mall. I don't do any of those, other than flying, very often at all. However my work requires me to fly, 757 usually, about once a month to either Orlando or San Diego, through Dallas. The planes have been jammed the last several times to both destinations.
Really. With all the inconvenience you'd think people would be taking surface routes instead of flying. Traffic must be amazingly bad out there.