Good to see LA is the most fuel efficient of the major US cities!
As for Houston and traffic jams, well...Houston doesn't have terrible traffic...but their freeways do have a tendancy to go from 80+ to 0 within a matter of seconds whenever there is an incident. You'll hear a lot of locals talk about how they "got caught in a parking lot" on their commute. I really don't think traffic in Houston is terrible. A little worse than average, but very doable. Hell, my aunt would commute from Houston to Tomball on a daily basis, and she never got too uptight about it. IMO, Atlanta definitely has worse traffic than Houston, but that's caused by the way people in Atlanta drive--very slowly and carelessly. They weave in and out of carpool lanes (shouldn't cross the double white lines) with abandon, poke along and then decide to cut over a couple lanes to get to their exit, and just drive like Sunday pleasure drivers at all times of the week.
While LA gets a bad rep as the most congested city (I wholeheartedly disagree), that's due to the metrics of that study--since LA is a geographically humongous city, and the metro area spans more than just the incredibly huge LA County (Ventura, Orange, parts of San Bernardino, etc), the "time lost due to congestion" is artificially inflated when some people are commuting to Los Angeles from Palmdale, Lancaster, Moreno Valley, etc. They already have a 2-4 hour commute, so they disproportionately affect the "time lost to congestion" since in heavy traffic due to incidents on the freeway it would not be uncommon to incur another 60-90 minutes on that, per leg. People in LA don't f@#k around with their driving--they will go as fast as they possibly can in every circumstance.