Someone up thread mentioned that it's upwards of an hour from SFO to downtown by cab during rush hour. I've been driving SFO to the 101/80 split during rush hour for six years now, and 45 minutes is the extremely rare very bad day. It's usually 20 minutes, and 30-45 if things are bad. Downtown is a little further, but most good cab drivers will get off the freeway as soon as they hit traffic, and keep the ride to 30 minutes or so. By contrast, Bart is 33 minutes with up to a 20 minute wait between trains, plus time to get to the Bart station (cabs are at every terminal, Bart is at one). A cab is almost always going to be faster than Bart, and is often twice as fast.