But what about the environmental cost/benefit? Is it a plus or a minus to have a second, presumably more efficient, car?
Current situation: Chrysler Town & Country ramp van. Driven 11,900 miles/year. It gets 19 miles/gallon. So, 626 gallons a year. Burning a gallon of gas results in roughly 19 pounds of CO2. Current total per year: 5.95 tons of carbon.
If we got a new car, let’s assume we’d still drive the T&C half the time (because of the wheelchair thing). Let’s also assume the second car is a Honda Fit. The math is:
T&C: 2.97 tons of carbon (half of what it currently uses)
Fit: 5,950 miles (11,900 / 2) @ 34 MPG: uses 175 gallons, which equals 1.66 tons of CO2.
Total for both cars: 2.97 + 1.66 = 4.63
So we’re 1.32 tons better each year (current 5.95 vs. new 4.63). Yea!
But, what about the cost of building the new car? That is not an easy question to answer. This uses an estimate of 720kg CO2e per £1000 spent on the car, which when converted to US measurements and based on an $18,000 Fit, comes to 10 tons of carbon. Oof.
So we pay a big carbon cost up front, and then get back a little each year. After 7 1/2 years we’re even, and after that we’ll be ahead of the game. Not particularly exciting.
The math for the typical driver is usually more compelling. For example, if we were just replacing the existing car, the break-even happens must faster (less than four years), because we wouldn’t be driving the old car at all. But since we don’t drive much, and still have to use the T&C at least some of the time, there isn’t an overwhelming environmental reason to make this switch.
