Plotting the efficiency of a commute
Posted January 18th, 2006 by Howard TaylerI’ve got a pretty good idea what kind of gas mileage Turbo Schlock (my 2003 GLS Turbo Beetle) gets. It’s around 28 on the highway, and 22 in town.
There are two routes to Dragon’s Keep from my house that take about the same amount of time. One involves 3 miles of town traffic and 6.6 miles of freeway traffic. The other involves 6.6 miles of town traffic.
It SHOULD be a no-brainer — take the shorter route, and save on gas money.
But let’s do the math:
3 miles divided by 22mpg = .13636(r) gallons of gas.
6.6 miles divided by 28mpg =.236 gallons of gas.
The freeway trip will therefore take around .37 gallons of gasoline. A round trip (assuming the same distance each way, which is close enough, even though the Center Street freeway access is at least a quarter mile longer in one direction) will take .74 gallons of gas, or almost three-quarters of a gallon.
6.6 miles divided by 22mpg gives us .3 gallons of gas, which is the total for the State Street route. Round trip, .6 gallons, for a savings of .14 gallons of gas over the freeway round trip route.
So I’ll keep driving on State Street. I don’t get to go nearly as fast, and some of the traffic is frustrating, but I’m saving about 30 cents each time I do it that way.
(then again… I have to ask whether saving 30 cents is worth the frustration…)
I’m such a geek.
–Howard
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January 19th, 2006 at 12:49 am
Actually, the only way to REALLY tell would be to drive each route for a tank of gas and see which gives you more round trips. “city” driving has way too many factors to make the published numbers mean much. I doubt you get the same MPG in downtown NYC in rush hour (when isn’t it rush hour there?) as you would in, say, downtown St. Louis at 3am.
Likewise, there are more factors involved in the highway MPG. I doubt you get the same performance in the loop around your city as you would, say, on an LA freeway during rush hour or driving in .
Just having more hills in one than the other can skew your results.
Also, remember that city driving has more effects on consumables than just gas…why, the cost in brake pads and high bloodpressure medicines alone….
I’m going to bed now. :)
January 19th, 2006 at 7:41 am
Since the freeway trip (at the time I’m taking it) is very smooth, I’m pretty confident in those numbers.
The State Street trip is also fairly smooth. The only stop-and-go is at the lights. You’re right, though — the only way to be SURE is to gather more data, and approach the problem from a different angle.
I’m a geek, but I’m not THAT much of a geek.
January 19th, 2006 at 10:31 am
Does TurboSchlock have the built-in trip computer that was standard in the 2000 Passat? I get “real-time” gas mileage readings (updated every 100 yards or so), plus trip details (miles, time, average speed, average gas milage, etc).
January 19th, 2006 at 10:45 am
Not that it has much to do with the gas issue (BTW, I have a gut feeling that you’ll probably spend more than the 30 cents idling in traffic), but your dragonskeep.com link has one too many e’s.
January 19th, 2006 at 10:50 am
Thanks, ThornyJohn –I’ve fixed the link.
Note also — both trips take almost the same amount of time.
January 19th, 2006 at 12:31 pm
The published Miles Per Gallon for a vehicle are what the government gets in labs under specialized
circumstances. Running anything in the car besides driving will lower those numbers. For example:
Running your Air Conditioning and Heating will greatly lower those numbers. The better your
standard gas millage the greater the drop for Air Conditioning and Heating.
The published numbers are meaningless for Hybrid vehicles. The government tests were not
designed for Hybrids and so report much higher than true results. Lets just say I am still bitter about
that bait and switch.
January 19th, 2006 at 1:22 pm
Miriam, I think Howard’s MPG figures were what he’s calculated.
FWIW, my ‘03 PT Cruiser averages combined driveing between around 20, depending on what I’m doing, where I’m going, and how heavy the vehicles are. (and also how fast I’m going too.)
And yes, the EPA test numbers are pretty much bogus. I ignored them when I went shopping three years ago, and went with practicality, sale price, and style. :)
January 19th, 2006 at 2:00 pm
My MPG numbers are based on the following:
1) Several freeway trips to and from SLC in which I clocked the mileage and then filled the tank again. This is a round-trip of about 80miles with maybe 4 miles of city driving thrown in. The result, when I’m driving reasonably, is around 28mpg. When I hot-foot it (80mph instead of the posted 65) my mileage drops to around 25mpg.
2) Months of “standard” driving, which included 7mile freeway jaunts and 5 miles of surface streets, all while I was commuting to and from Novell. Mostly I hotfooted it on the freeway — it’s nice living where the commute actually GOES that fast — and the result was about 24mpg for the combination.
3) a couple of tank-fulls of “city-only” driving. Now that I no longer commute to Novell I have few reasons to take the freeway. Everywhere I need to go is most easily reached by surface streets. The MPG for those tanks was around 22mpg.
#3 depressed me a little bit, until I remembered how little I was actually driving. I only need to fill my 12 gallon tank about twice a month, max. I drive the kids to school each day, and I’m hitting the Keep about three days a week lately. So I’m using a LOT less gasoline than I used to.
January 19th, 2006 at 5:03 pm
Did you take into account the relative wear and tear on the car, which surely will be more in the city, with increased braking, steering and gear changes? Can you find a formula to include them in your calculations?
January 19th, 2006 at 5:19 pm
Nope. But since I’m driving less than 500 miles per month, I suspect that routine maintenance isn’t going to be an issue for a while.
January 19th, 2006 at 5:55 pm
The EPA numbers do not account for your personal driving style. For instance, I like to use Neutral and coast up to stop signs/lights instead of racing up to hit the breaks, but when the light turns green I take off (unless I can see the next red light) However, the EPA numbers are not designed to tell you what kind of mileage you will get, they are specific test under specific conditions to allow comparisons between similar vehicles. So do not com,pare a minivan’s epa ratings to that of the TurboSchlock, and only compare a hybrid to another hybrid.
Personaly, I think they should place the scaled ratings like they do on appliances:
In Vehicles of this class (Turbocharged 4cyl Compacts) this vehicle rates:
|—————————-|
^——–^
20 22 28 35
city hwy
January 19th, 2006 at 6:13 pm
Regarding the comment about hybrid vehicles.
My wife and I own a 2005 Prius and around town in Seattle we consistantly get 42 to 42 MPG.
And on long Hwy drives to visit friends we see 50 to 55 MPG. the higher MPG however is only
with the cruise control set at the speed limit. So the moral is, drive safe, drive sane and
drive the speed limit.
Your mileage may vary.
January 19th, 2006 at 7:55 pm
Wear and tear on the brakes.
Wear and tear on the transmission. (stop and start)
Wear and tear on Howyrd’s heart. (traffic = stress = bad!)
Drive on the freeway, stay alive!
Mew
January 19th, 2006 at 8:35 pm
Constant acceleration and deceleration will affect your milage, on the highway if you maintain constant speed, you’ll get far better milage.
That, and you’re running a turbo if I’m not mistaken… keep it under revved and drive slow without laying on the boost, and you’ll get better milage… this would tag back to constant acceleration in city driving.
January 19th, 2006 at 8:38 pm
I love the way you think! :)
Highways do have a better safety record than local roads. I usually prioritize first on time, then on comfort/convenience, then on gas mileage. Between my house and my boyfriend’s (halfway across the state), I find the highway takes 1:10 for me, except during rush hour. The back roads always take 1:30, so during rush hour I go that way. My fuel efficiency is *better* on the back roads b/c of the 45mph posted speed limit / 55mph actual travel speed as opposed to the 65/75 on the highway. I haven’t checked the actual miles.
Summers I’m more likely to take the back roads b/c the road conditions will be good and I can put the top down on my convertible. But that adds 2mpg, so it’s a trade off.
January 19th, 2006 at 8:47 pm
For that distance, you could always get a scooter. http://www.yatahonga.com/images_22510.html (Which could be anything from 50cc to 650cc, but at least 200cc for the freeway option.)
January 19th, 2006 at 11:29 pm
Calculating milage is always a bit tricky. For example, my 2004 Honda Civic is listed as getting 32 mpg city, 37 mpg highway. The actual numbers:
1.5 mile commute to work (city driving): 22 mpg
6 mile drive to my uncle’s house (city driving): 30 mpg
Long-distance highway driving: 35-40 mpg
Forest Service roads (I do a lot of hiking): Upwards of 45 mpg
Idling/low-speed driving also takes very little gas. An hour and a half of driving at
January 20th, 2006 at 12:25 am
I despise the ProvOrem Commute. In general, I find I spend the least time at stoplights, thus the least frustration and gas, by taking State street south and University Parkway North (Too many uphill stoplights on State Street going North into Orem) I tend to cut over from State to University depending on which light I catch, which usually means that I cross over about 960 or 800 North to get to campus.
Friday Nights however, are the worst. From Dragon’s Keep I’d probably go directly to the freeway or take University Avenue all the way North to the end rather than fight traffic on State and Parkway. Who needs more stress?
January 20th, 2006 at 7:04 am
Another method to truly determine the gas usage would be to drive to the nearest gas station and ensure the tank is full, stopping when the auto-shutoff valve kicks in. Then drive the round trip and return to the same gas station where you started. Refill and note the amount of gas. Repeat with alternate route.
Ta-da! Your actual gas usage, less any variance in when the auto-shutoff kicks in.
January 20th, 2006 at 7:07 am
Vale: My return trips from the Keep are always after 7:00pm, so traffic is low. On Friday nights they’re usually after midnight, when our gaming session lets out. Traffic is all but nonexistent.
Ed: Well, yeah. That’s how I fill the tank every time, and I always make note of what the mileage was like for that fill-up — even if I only went a few miles.
January 20th, 2006 at 7:10 am
I think I’m missing something – the shorter distance is, in fact, saving you gas – unless I’m making a bad assumption when I see “it SHOULD be a no brainer – But let’s do the math” and think “okay, so it’s not the expected result
January 20th, 2006 at 7:12 am
Weelll…. this might sound somehow … don’t know … like i’m patronizing you, but it’s not meant that way, trust me.
But I think you could save _a lot_ more by driving the right car. I just made a quick computation and realized that (supposed 3,78liter = 1 gallon and 1,609km = 1mile) my car goes 52 miles with one gallon, or (as we in old central Europe like to express it), I need 4,5 litres per 100km — Diesel.
My car (Opel Corsa CDTI) cost less than yours, has just as much space inside, a bit less horepower (52kW, about 75PS) but due to the fact that it is a turbocharged Diesel engine, at least the same amount of torque and nice acceleration! … well, and I only need half as much gas. — oh, you could get the same car with 70kW and same fuel consumption, as long as you drive sensible.
If you want to save on gas, start with the car!
Don’t know what the US market looks like, but over here, the market is full of turbo-Diesels big and small.
Some people save a lot on a “cheap” car but don’t realize that half the bill is paid at the gas station. On your side of the big pond probably less so, but nevertheless. That’s not to say you should give Turboschlock away … you probably wouldn’t do that anyway. But in general I think it’s wise to make a quick calculation of gas plus acquisition costs before buying a car.
And the second thing that could save a lot of additional fuel costs is the right driving style. Avoid using the brake if you can just let the car roll out with “motor brake”, in general, try to keep your velocity as constant as possible … and always use the highest gear that will deliver the power you need at a given moment … and that means 5th gear at 35mph constant speed! This can save another 10 to 20% fuel cunsumption (and no, it doesn’t damage the engine if it’s been build after 1985) and works on any car :o)
January 20th, 2006 at 8:39 am
Before y’all yell at the nice VW driver, please consider the following. He DOES math.
The whole conversation in a country where people buy HUMVEE as a status symbol (rather than as proof of delusional militarism or poor math skills) is silly. Mr. Taylor actually did the math for his commute — and he is probably also aware how rare diesel vehicles of any sort are in the USA. This makes them very hard to buy, and they tend to carry a premium of several thousands of dollars. This year, the only diesel in the USA at the dealer are VW jetta, golf, beetle, or passat, all “TDI” Assuming his current burn rate of 25 gallons of gas a month and midprice gas of 2.5 dollars / gallon and an automotive life span of .. oh .. lets say 10 years, his total fuel costs should approximate 750/ year or 7.5k. A diesel would save him several thousand dollars as they tend to get about 30 mpg city and 45 country. Properly, this would reduce fuel consumption by a third. Diesel fuel carries a premium of about 10 percent to 20 percent at the pump per gallon, too, which means that at the end of a decade of driving in his diesel, he would be ahead at the pump by an impressive 200 / year or 2k. A hybrid would be a similarly unimpressive saving — especially when you factor in the replacements of the battery system every 5 or so years, and the large premium up front (more than offsetting goverment incentives) A pure electric care would actually be surprisingly possible — there are conversions which can be put into a prius to run it like a pure electric for distances under about 50 miles a day.
To own YOUR car would cost Mr. Taylor, roughly, 4 or 5 grand more than his current vehicle. Some states in the USA actually carry restrictions against sale of new light commuter diesels (e.g. California uzw.) because of many environmentalist claims against diesel supported by the unlikely Detroit industry.
January 20th, 2006 at 11:08 am
Zak: Don’t make me come over there.
The math I’m doing is there to help me economize within a certain set of pre-existing conditions.
Besides, I did the math when I bought the car. Based on new car purchase price, over the life of the car (10 years) the price of fuel (based on 10,000 m/yr) and the difference in gas mileages between TDI and T/GLS, the savings for TDI would be less than 5% of the purchase price of the car.
In short, I decided to pay more for a car that performs better.
Note also that diesel in the US is a lower grade diesel than in Europe. The TDI engines VW ships over here are more tolerant of the crappy fuel they’ll be drinking, and get worse mileage AND worse performance than the same model car in Europe on European diesel.
Besides, for the miles I drive (not many, these days) it’s almost irrelevant. I spend less than $40 per month on gasoline, and I have a car that can blow the doors off of about 90% of the other vehicles on local roads. I usually choose NOT to, but it’s nice to have that under the hood.
–Howard
January 23rd, 2006 at 2:12 am
I think I’d really appreciate you coming over here, but that probably wasn’t meant that way.
Alright, I didn’t know the fuel prizes in the US — I knew they were smaller than here but under these circumstances you’re probably right … I pay about 1,3 USD per litre, that’s about 5 Dollars per US-Gallon, and Diesel’s cheaper than “regular” gas. Neither did I know of penalties for TDIs
I didn’t mean to say that the beetle is an economically bad car, sorry if that came out wrong!
Also, probably the beetle is less expensive in the US than other VWs, since it’s being produced on your continent, contrary to many other VW models — over here, a Golf would be a more sensible choice, costing less and delivering more (space, speed, power, efficiency), but then I have no idea what it would cost you.
Thing is, I’m seeing people all day who buy their car for looks and power, drive like there’s no tomorrow and later complain about the gas bill … and that applies everywhere, I guess. Over the last few years the average fuel comsumption of cars sold on the European market hasn’t changed much, despite cars having become more efficient. It’s actually hard to find cars who convert the technical advance into economy instead of horsepower, and even harder to find people who would buy them. Thus my message is: Go do the math when you buy a car! That will be a different one depending on what you need it to do and what the boundary conditions are, of course.
In short: I just wanted to share some experience I have gained in dealing with the problem, and I apologise for any attempts at being witty in a foreign language.
– Zak
January 23rd, 2006 at 6:32 am
Well, I’m one of those ‘buy for the power’ types.
I own a ‘95 Buick Riviera that will beat nearly any other
car in this area from the line. After a few affordable
upgrades, I have better traction, more power, more stability,
and even some improved fuel milage from stock. I commute 50+
miles for work, and with a mere 19.2 gallon fuel tank, I need
to refuel weekly. I need to use 93 octane, prefer it to contain
Ethanol, as in this motor it improves both power and milage, and
I get about 15mpg city. This car has a federal rating of 20 city. In
it’s life, it never achieved that, as traffic in this area is rediculous.
Prior to the minor upgrades, I would not see better than 13 on a
good tank going into the city. highway I am able to easily get 30+
MPG at 90+ MPH. With the after market products available today,
any vehicle can be ‘convinced’ to perform how you want it to. it’s
simply a matter of choosing…’Do I want power, or fuel economy?’
I think it’s fairly obvious which my choice is…As a great man (Tim
the Toolman Taylor) once said…”Mor power..ur ur ur urur ur!!!!”