Only in America does half of the roadgoing public use equipment designed for use off-road and consider that a best practice. Is there a headsmack emoticon on this forum? I see petite women in office dress piloting massive SUV's, a single wheel of which requires 10 horsepower just to overcome static inertia. This makes sense? I flatted once on the inbound leg of my suburban commute, and while changing out the tube I was passed by a fair assortment of other commuters, and the number of them that were riding on full knobbies... ... that whine you hear from your knobbies... ... that's energy. Your energy.
If you don't have any better use for VO2 max than heating up air molecules can I have some? Please? I'm at the age where energy matters. My wife... ... never mind... people, they call them mountain bikes for a good reason. If the highest gear on your commuter is 78 gear inches you just might be having a sub-par commuting experience. You don't have to have drop bars. Plenty of road bikes have flat bars. But they will "usually" have longer cranks, higher gearing, narrower rims and tires and that's HUGE.
The corporate types that drive Hummers have mainly higher fuel costs to illustrate their impracticality. The price to a bike commuter is more physically direct. Newbies don't know that. They read these forums and go out and perpetuate the madness. If I keep even one newbie who is on the fence over what kind of bike to use from rushing out and putting another full knobby, under-geared and over weight MTB relic from the early 1990's on the road, I can go to my final reward with my head high and my conscience clear. FWIW.