My Prius experience

Almost 6 years ago, in September 2004, I was intrigued by the Toyota Prius and put myself on one of the waiting lists for a car. Somewhat unexpectedly they actually had a car for me by April 2005. It was a delight from the moment I first test-drove it, and the only car I've liked more in the time since has been a 2010 Prius I was a passenger in earlier this year. It wasn't just the fancy hybrid electric drive, nor being able to ride in the expressway HOV lane any time I want, joyful as those things might be. Somehow the car expresses a compact perfection that's hard to put into words. The interior is spacious, the seats comfortable, the controls (dashboard and all over the steering wheel) easy to reach and intuitive. The digital speedometer and other urgent indicators above the main dashboard give a different feel from other cars I've been in, one that emphasizes what's important, and lets you ignore the irrelevant. The keyless entry and push-button ignition (thanks to an RFID key that never leaves my pocket) spoil me for other cars I have to drive on occasion.

But the meat of the car is the hybrid engine and fuel efficiency. So how does that do? The dashboard monitor tells me how I'm doing, usually somewhere between 40 and 50 miles per gallon. But I wanted to keep better track, so after my first year I decided to start recording my gas purchases; the following graph shows the record:

The dark blue line is the main one of interest - that's the average miles-per-gallon over 3 fills of the gas tank. The green line with considerably more variation is the single-fill average. I'm assuming that bounces up and down mainly because a fill isn't entirely well-defined, so sometimes the total in the tank after filling it is more or less than the average.

The main feature I notice in this is the seasonal variation: the MPG curve dips down to just a little over 40 MPG in mid-winter (January each year), and gets back up close to 50 somewhere in the middle of the year (though the peak seems to vary from June to October). I'm pretty sure this is due to the use of the car heater - when the heater's on, it forces the gasoline engine to turn on, even if the car otherwise doesn't need it to go anywhere. That defeats much of the purpose of the hybrid. But it does freeze here in winter, so heating's important...

There is also a very slight downward trend in my data. For the incomplete year of 2006, I was averaging 48.1 MPG (but that's missing most of the winter months). For 2007 the average over the full year was 46.4 MPG, for 2008 it was 45.4, and for 2009 it remained about steady at 45.5. For 2010 so far it's 43.9 MPG, but we have some warm months still to come to make up for the early part of the year, so perhaps it'll return to the 2008-2009 average. The downtrend could be just because the car's getting old, perhaps it doesn't slip through the air like it used to, or some mechanical parts are causing more friction than they should. It also could be due to changes in the pattern of my driving.

The light blue curve shows the average (over 3 fills) of the miles I drove per day at that time, and that shows a slight upward trend over the years. Part of that is from driving kids around more as they've been getting older; also November 2007 was the start of my regular gym attendance which has meant 2 short hops in the car most mornings.

The red curve is the price per gallon at the pump. Integrate all three curves and you can find out how much I've spent on gas over the past 3 and a half years: $3815. If I'd done all that driving in our minivan (18 mpg) the cost for gas would have been $9615, or an extra $5800. Of course if I didn't have the Prius I'd surely have picked a more efficient car than that - but it also wouldn't have been as fun to drive.

Anyway - I was chatting with a couple of old guys the other day who were reminiscing about their pickup trucks. Maybe I'll be that way about the Prius some day. Maybe I already am... it's definitely still a fun car to have 5 years later, whether or not I get to be smug about it :)


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Have you seen the South Park

Have you seen the South Park where they make fun of smug liberal hybrid drivers?

No but I can imagine it :)

No but I can imagine it :) What I can't imagine is why conservatives would want to waste their money on gasoline to fill up their pickup trucks and SUV's just for image reasons... - I mean, we're talking thousands of dollars a year here. Don't you have better things to spend your money on? Investments, that sort of thing?

And it really is a nice car (the 2010 model even more so)...

So if you do an NPV

So if you do an NPV calculation, the hybrid is the better choice?

Well, the value of a car

Well, the value of a car itself is somewhat subjective (how much is a comfortable seat, or perks like keyless entry, worth?). However, the car I bought for $23,000 in 2005 currently retails for $11,573. Maintenance has been quite inexpensive, insurance isn't bad (Prius's are rarely stolen, so comprehensive rates are lower than for some cars).

But suppose I'd purchased a Ford F-150 instead (the most popular vehicle in 2005). I don't know what prices were in 2005, but the lowest end model this year costs about $21,000. Resale for the cheapest 2005 model is about $8500 now. Fuel economy was 15 mpg; about 1/3 of the Prius, so I would have paid over $7000 for the additional gas for the driving I've done.

So, I paid an extra $2000 on initial price of the vehicle, but it's worth $3000 more now, plus I've saved $7000 on gas, and likely some savings on maintenance and insurance as well. I think I'm up at least $8000 relative to the pickup owner. And I haul tons of stuff around in the Prius - just this morning I loaded it with 7 50-pound bags of concrete and 3 60-pound bags of gravel, plus tools, etc. And it carries my kids around too with the backseat up... I really have no need for the pickup.

That's the most miserable

That's the most miserable comparison you could have made. I realize that there are no direct comparables, but try your best. Why not compare two sedans at least? Just give features like noise versus acceleration or something a wash. Note them and discuss. But note both ways (even for your pickup example, you note none of it;s advantages. Try to do it both ways, like a thoughtful business analysts).

Also, your entire analysis has NO use of time value of money in it.


Who knows...maybe NPV shows you are RIGHT!? My point is not to prove right or wrong per se. But I'm kind of in shock that you don't do intuitive little business cases in your head. I mean I do stuff like that everytime I buy a coffee...

What's a comparable vehicle?

What's a comparable vehicle? I talked about pickup trucks in the article, and guys reminiscing about them. And I was comparing to the SUV crowd. I picked the cheapest version of the best-selling vehicle of 2005. Seems a pretty fair comparison to me. And I included time (3.5 years for the mileage data I had - though it's actually 4.5 years for total car life so far, since I'm missing the first year's mileage) a dollar investment amount ($2000 additional) and a return so far ($8000). I make that between a 37% and 49% return on the marginal added investment, but you may want to compute differently, have at it.

Various consumer magazines do basic cost-per-mile analyses of vehicles, supposedly including depreciation, wear and tear maintenance costs, insurance, and gas. Usually something like a bottom-end Honda Civic or Ford Focus comes in as best. But is it a comparable car? I really like my Prius, just like the old guys I talked to liked their pickups. There's a reason we don't all buy the same vehicle...

A comparable would be the

A comparable would be the closest similar car with a conventional engine. Duh! Not a truck. You're confounding small car versus truck with hubrid versus normal engine! Grr!

And you still didn't think about time use of money.


Well of course it won't price

Well of course it won't price well compared to another sedan. The hybrid part is expensive.
For an extra $5800, I'd rather have the minivan.

Arthur, I've had my Prius


I've had my Prius since June of 2004 and have also kept track. Here in Rochester, the seasonal cycle in the MPG is even more pronounced. It may be due to more than just the heater...I think the engine also has to run a certain amount to warm up in order to satisfy the stringent SULEV (or whatever it is) emissions standard. And, I have heard it suggested that the batteries are less efficient in the cold and even claims that the increased air density & resulting drag makes a difference.

By the way, I recommend also recording the average MPG as computed by the Prius screen each time you fill up. I think this number is actually much more precise than what you get by calculating the MPG yourself (because of the variability in the amount of gas you can get into the tank...which is probably even worse for the Prius than most cars because of that bladder thing in the gas tank). As a result, you should get a much less noisy curve using that number even without having to average over multiple fillups. (The value for the amount of gas used in computing that average MPG is apparently calculated by integrating the amount of time that the fuel injectors fire, which I have read should indeed give very good precision...although its accuracy may be a little off, i.e., there may tend to be a small offset relating to variability in the injectors relative to specs. In my experience, the offset over the long run in comparison to the direct calculational method is that the screen MPG is high by about 1.2 mpg, or ~2.5%. Of course, I don't even know to what accuracy the gas pumps at gas stations can be trusted to.)

I have also seen a decline in MPG with time; however, mine seems to have been sort of a step function that occurred when last spring/summer my MPG failed to recover nearly as well as it had in previous years. I got new tires that spring, so that's the prime suspect...although I am surprised that the difference is that dramatic (about 5-6 mpg drop in the summer compared to previous summers) and the tires that I got (Uniroyal Tiger Paw) were rated well for rolling resistance. I was also wondering if there was a change in gas formulation, particularly with the use of more ethanol in the mix, that could account for it. Or, maybe something with the car aging or getting out-of-tune. Of course, it is the funny thing about owning a Prius that one finds little sympathy from people when you tell them how your gas mileage sucks because you used to get in the low 50s in the summer and now it is down around 45-47 mpg!

I agree with you that the Prius is a great car. People are always surprised by the ample rear leg room and the very decent luggage space. And, the hatch is long enough that I can put my bike in (with the seats down, of course) without taking off either of the wheels. A few minor annoyances, as with any car, but I am generally very happy with it.

Hey, I didn't know you had

Hey, I didn't know you had one too! Ownership seems to be infectious - my father and sister have bought Prius's, as well as at least one brother-in-law. The roomy interior really is impressive - people refer to it as a "small" car, and I think the pre-2004 or so models were smaller, but mine has plenty of room for pretty much anything I want to carry (well, except my whole family doesn't fit, but that's true of almost every vehicle - it's tougher than you might expect to get a rental guaranteed to carry six plus luggage).

So do you have any graphs of your Prius data? I'd be happy to post here!

Arthur, I have an Excel


I have an Excel spreadsheet but I haven't entered the data from the pen-and-paper record that I keep in my car for about a year. Let me get it up-to-date and then I'll send it to you.

Heh, my sister just bought

Heh, my sister just bought one because her company moved her office from about 10 miles away to a gruesome 35 mile one way commute in stop 'n go traffic (I had a slightly longer version of the same commute, end point a few miles farther up the same boulevard). One of the reasons she got the Prius instead of the competitors was because she could fit her stand up bass in the thing. Talk about rear legroom! Overall, Toyota has done a great job of packaging the car.

About your mileage. You would be surprised about the differences in rolling resistance of tires. If you got tires which have good winter traction -- M+S rated -- they will have higher rolling resistance. I believe that Toyota had some special OEM tires with very low rolling resistance designed for the Prius, so this could well be the reason for the decreased mileage.

Me, I'm kind of a leadfoot and I like the feel of G's when I put my boot into it. That and sharp cornering performance. My favorite car for this was my heavily modified Mazda Miata. 0-60 was around 6 seconds and it would pull close to 1g in the corners. Fun, fun, fun, and I still got around 25mpg in mixed driving, over 30 on the highway. Moving to a place with snow on the ground for close to 6 months of the year (last year it was October to May, a long winter by anyone's definition) moved me to sell my baby and just use the Subaru. It sill gets 25mpg in mixed driving with my leadfoot and 33 -35 on the highway. I hope Suby has a hybrid by the time my current one dies, but that is years in the future.

I love the way the car trains

I love the way the car trains you to get higher MPG.

Or, maybe something with the

Or, maybe something with the car aging or getting out-of-tune.

Aging batteries causing the engine to run a bit more frequently than when they were new, perhaps?

Just out of curiosity, could

Just out of curiosity, could the MPG reduction during the winter be related to the presence of ice and snow? It is true that people drive more slowly in such weather (or should!). but it also requires more time to cover the same distance and detours are often more unpredictable. Snow and ice can also accumulate on the car and add more weight.

Not where I live, we only get

Not where I live, we only get a couple of weeks of snowfall in a year. It could be related to having more rainfall though, if driving in the rain is causing the problem. I don't think it could be humidity-related though (summers are much more humid).

Hello. I apologize for the

Hello. I apologize for the belated response: Life has been rather hectic! I just wanted to explain that I had observed that the highest mileage spike was in January 2008 which was followed by a sharp decline. I thought that could be attributed to the massive blizzard that occurred that winter, but I have just consulted the weather records for 2008 and discovered that the blizzard did not actually strike until March. (I also do not know how it affected your area.)

I did have one other question. Cold air is denser than warm air and daily winds are often more powerful in winter than during any other season. Could this increase in air resistance be sufficient to significantly affect your mileage?

Be sure to let us know if you ever unravel this mystery. ;-)