Dear Science,
What’s up with these hybrid cars? Are they really all that green
and deserving of tax credits?
Sincerely,
Lambo
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,
Science
