Energy savings
According to Google Maps, the airport is 37.4 miles from our house, so round trip is 74.8 miles. The family car is averaging about 21 mpg these days, so that would be 3.6 gallons of gasoline. We used about a quart of gas getting to the train station and back, so the total gasoline savings was 3.35 gallons. According to the EPA's website, the average amount of CO2 emitted per gallon of unleaded gasoline is 19.4 pounds. (This figure could probably bear further scrutiny in a later post.) So we emitted about 65 fewer pounds of CO2 than we would have had we driven to the airport.
According to this site, household electricity costs about 1.5 pounds of carbon per kilowatt-hour, so by way of comparison, 65 pounds is about the same as the emissions produced to power my air conditioner for 11 hours or if I left every light in my house on for 24 hours. (More later on emissions from my electric company.) In an average month, we use something like 55 gallons of gas, so taking the train instead of driving cut down on monthly gas by 6%.
Cost savings
At $2.71 a gallon, the trip would have cost $9.75, plus $49 for economy parking. We spent 65 cents on gas, plus $8 on the train (I have a student pass), so we saved 58.75-8.65=$50.10.
Findings
I don't think it was worth the extra time and hassle, though my 2-year-old was in heaven riding a train, bus, and airplane all on the same day. Because we were riding in the middle of the day, both the train and the bus were mostly empty, so there was plenty of room for our luggage. But on the way home (after being up since 2:30 am with aforementioned 2-year-old) we had to wait 25 minutes for the bus, then another 20 minutes for the train. All told, we tacked on an hour and a half each direction to our trip. And getting one large suitcase, three backpacks, a stroller, a car seat, and two kids on the bus was a bit hair-raising too. Next time to save on money, I think we'll ask my brother to drive us to the airport. I think I'll wait for the light rail to the airport before attempting to ride public transportation to the airport again.
Like I said, next week I'll look more closely at public transportation. In this post I assumed that since the train was running whether I was on it or not, our riding it added no carbon emissions to the atmosphere. Next week I look at whether the train is an efficient means of transportation or not.
The EPA number definitely does require further scrutiny. If, as you say, a gallon of gasoline emits 19.4 lbs of CO2, you have created approximately 11 lbs of byproduct from thin mountain air - a gallon of gasoline weighs less than a gallon of water, 8.3 lbs. I think what is meant is that it takes about that much CO2 to produce that gallon of gas. But that also seems odd. It doesn't seem to be a very efficient product, if it takes more energy to produce the gallon of gas than that gallon of gas produces (as interpolated from the emmissions - more emissions equals more energy?) Very odd, that statistic.
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