Way back in 1996, my parents decided to buy a
minivan. I was in middle school, so I don’t remember much about the decision-making
process, but it had something to do with taking more family camping vacations
and wanting a new vehicle that was versatile and reliable. Apparently they did
their research, because today I am still the happy driver of a 1996 Toyota Previa with 200,000 miles and counting.
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| Meredith and her husband with their Toyota Previa at White Sands. Photo by David Morrison |
You’ve probably seen these funny, almost retro
egg-shaped minivans now and again. They were only sold in the US between 1990 and 1997,
and had a unique mid-engine design. Today, Previas are well regarded as over-engineered
proverbial tanks: with regular maintenance and a bit of luck, many survive well
into their 300,000s.
Once my family decided on the van, my mom called
nearly every Toyota dealer in the state. When they asked her what color she
wanted, she replied “anything but plaid!” My dad purchased a little
spiral notebook that would live in the glovebox. On the drive home in our new
Previa, I remember stopping for gas. Dad broke out that little pink notebook
for the very first time and began recording data.
Of course, once you begin taking data every single
time you buy a tank of gas, you can’t just stop. He really enjoyed calculating
the mileage every now and then, and insisted that my mother also painstakingly
record data every time she bought gas. When I got my driver’s license many
years later, my handwriting joined theirs in the pink notebook. Eventually the
Previa came with me to college in California, and has been with me ever since. Now
in New Mexico, my husband drives the van most often and has carried on
our slightly-silly tradition of recording miles driven, gallons of gas
purchased, and money paid.
One day in 2012, on a long and boring drive to
Albuquerque, I decided it was time to do something about all this data. So, I
typed it all up (while grumbling about Mom’s handwriting, Dad’s imaginary 25-gallon
tanks of gas, my husband’s disregard for lined paper, and my own dyslexia). It
actually took that trip to Albuquerque and another to Tucson to enter all
200,000 miles worth of data, and I have a new respect for people who do data
entry on a regular basis!
Without further ado: the results!
[note: the Previa's EPA fuel economy rating is 17 MPG!]
Some key moments in the Previa's MPG history
June 1996, purchased in Spokane WA
August 1998, road trip with pop-up camper to southwestern US
December 2000, rear-ended by a bread truck
July 2002, road trip with pop-up camper to northern CA
May 2005, road trip to southern CA
June 2007, moved to Claremont CA
May 2008, moved to Richland WA
August 2008, moved to San Diego CA
August 2010, moved to Las Cruces NM
May-August 2011, traveled while van stayed parked at home
It is fascinating to see how the price of gas has changed over time. I suspect this is largely influenced by geography, as gas is taxed differently in different states. However, a dramatic drop in price was seen in late 2008/early 2009 while the van was in San Diego. This was a country-wide gas price drop.
There is a clear seasonal
trend with mileage, as with all vehicles: they run more efficiently in warmer months and
less so in colder ones. There is also a lot of scatter. Some of this may
come from errors in data entry (either recording or transcribing), or from not
filling the gas tank to the exact same level each time (my dad tends to top off
the tank when he fills it, while I prefer let it be done when the pump clicks
off). The larger scatter during summer months is mostly due to the aforementioned road trips!
Some of the other variables that contribute to
scatter include: highway vs. city driving, running the A/C, individual driving
styles (e.g. see Berry 2010), quality/octane of gas in different geographical regions (we always purchase
the cheapest regular gasoline), tire pressure, other maintenance-related
factors, whether we were towing a pop-up camper (and thus using the “overdrive”
setting), how much weight is being carried, humidity and weather… what factors
can you think of that affect mileage?
Meredith Rawls is a PdD student in Astronomy at New Mexico State University
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Well _of course_ you record the date, mileage, amount, price per gal, total paid, and location of every gas purchase in a spiral note book you keep in the glove compartment of every car you have ever owned, just like your parents did since before you were born. And when your kids learn to drive and borrow the car, you make them do it too. Doesn't everybody do this? What, they don't?
ReplyDeleteOf course, the data sits in a pile in the basement unanalyzed. That part of it I didn't pick up from my dad. Though one year I did use it to figure out my carbon footprint.