Dear Science,

What's up with these hybrid cars? Are they really all that green and deserving of tax credits?



Dear Lambo,

Carrying around a couple hundred pounds of you in a couple thousand pounds of steel, rubber, and glass is utterly insane. Because the universe is an ornery place, and nothing—a car, you, the Seattle City Council—will move without prodding. Things at rest want to stay at rest, and anything moving wants to stay moving in a straight line. It takes energy to start and stop, and to bend around curves. Zack's second law tells us the cost of changing momentum: The heavier you are and the more the motion changes, the bigger the cost.

So, the energy used to get you and a car moving from a stoplight mostly goes into moving the car. (Moving you is an afterthought.) Once moving, the car wants to continue in a straight line. The tires drag the car around bends, losing energy as heat in the effort. Every stop converts the energy as heat on the brakes. Electricity, gasoline, diesel, steam, prayer—no matter how the engine is powered, it is the massiveness of the car that costs.

The big idea behind hybrids is to capture a fraction of the energy lost during breaking by adding about 100 pounds of batteries and another heavy motor. For a certain kind of driver—say New York City cabbies, with lots of linear stops and starts—the energy savings can be meaningful. For the overwhelming majority of drivers, the gains are modest at best—little better than driving a small conventional car. Too much momentum is lost in curves; the energy recapture is too modest to overcome the energy it takes to drag around even more crap while moving little old you.

I won't even bother working out the numbers for diet-cola-and-extra-large-fries SUV or luxury ("V-12 power with a V-8!") hybrids. Looking at real-world tests and after generously rounding up, the best-in-the-pack Prius gets around 50 miles per gallon in mixed driving; the similarly sized Yaris gets about 40 miles per gallon. Yes, the Prius is better, but is it anything really different? For a 50 mile weekly commute, it still costs 31,000 calories from Saudi Arabia, plus the environmental damage done by road building, traffic congestion, parking lots, and so on. In comparison, 31,000 calories burnt by you on a (biofueled) bicycle would net you over 900 miles of commuting.

A sustainable commute is radically different: carpool, take the bus, ride a bicycle. Use the money you'd spend on gas, insurance, and a car to move within walking distance of work. Limiting how often you crawl into your private two tons of absurdity to go to work or the store is the key to an environmental lifestyle. So, no, hybrids are not green. Hybrid owners should pay for their delusions—no more tax credits, world.

Momentarily Yours,