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The W - Random - Car Question
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samoflange
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Since: 22.2.04
From: Cambridge, MA

Since last post: 281 days
Last activity: 274 days
#1 Posted on | Instant Rating: 8.62
I am not a car guy, but have recently found myself with a 30-45 minute commute. I've got a question for those of you here who know a bit about cars.

I can take two routes to work. Both routes are the same for the first 5 miles and the last 1 mile.

Route 1: 13 miles total, using 35 mph roads with 7 additional traffic lights.

Route 2: 17.5 miles total, using a 65 mph highway.

I do try to stay aware of braking too much, accelerating up hills properly, and other mpg boosting tricks. On the highway, I also cruise at 65 mph to boost mpg. I have driven each route for several weeks at a time and calculated mpg for each. It happens to work out that even though the highway route has higher mpg, the increase in distance makes up for it and I burn the same volume of gasoline for both routes.

Since the fuel savings are a wash, would one of these routes be preferred from a maintenance/reliability stand point?



Lloyd: When I met Mary, I got that old fashioned romantic feeling, where I'd do anything to bone her.
Harry: That's a special feeling.
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Zeruel
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Since: 2.1.02
From: The Silver Spring in the Land of Mary.

Since last post: 3 days
Last activity: 9 hours
#2 Posted on | Instant Rating: 5.03
Just curious, but what were your MPG numbers? How did you compute your MPG? Did you drive the routes on a full tank, fill up completely, then divide the distance traveled by the gallons purchased?

I'm really curious because to drive the 4 extra miles at 65 MPH it takes less than 4 mins. If you hit a red light at all 7 intersections, depending on their timings, you could spend anywhere from 3.5 to 14 mins idling (based on 30 seconds to 2 mins sitting for each). That will eat up gas if it's a big engine (6-8 cylinders), not so much for a 4 cylinder car.

My first instinct is that route 2 is better on the car, especially if it is a manual and not automatic. Because you're mostly cruising at highway speeds, you're not always shifting, and you're cruising at low RPMs in a high gear longer.

I have a V8 Mustang and I've really had to change around my driving routes to do as much high speed driving, less stop and go, and to avoid as many left turns as possible (esp with red turn arrows). They're not the same routes as yours but I was faced with a similar problem and my route 1 gave me 18 MPG, my route 2 gives me 22.5 MPG. Over 13 gallons a full up, that is a difference of almost 60 miles, and about $12, a tank.



-- 2006 Time magazine Person of the Year --
Fuelly
-- July 2009 Ordained Reverend --
AWArulz
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Since: 28.1.02
From: Louisville, KY

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#3 Posted on | Instant Rating: 5.18
It is my understanding that a somewhat lower cruising speed will boost mileage as well, so you might try it at 55 instead of 65. You might spend a few minutes longer, but I think you'd find increased mileage.

(edited by AWArulz on 17.6.11 1051)


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samoflange
Lap cheong








Since: 22.2.04
From: Cambridge, MA

Since last post: 281 days
Last activity: 274 days
#4 Posted on | Instant Rating: 8.62
My mpg numbers were based both on an on-board readout (I have a Saab) and my own calculations of filling up, driving to work for a week (no other car usage or side trips), filling up again, doing some long division. The calculated numbers always match up very well with the car's readout (p-value < 5% --> I'm an engineer!), so I'm confident in the accuracy.

Route 1: 13 m / 21 mpg = 0.619 gal
Route 2: 17.5 m / 28 mi/gal = 0.625 gal

I have a small hatchback with a 4-cylinder engine and automatic transmission.

I work earlier hours than most commuters, so there isn't too much traffic. So, I maybe hit 3 red lights out of those 7, and most of those I can see from way ahead and will coast instead of maintaining speed all the way up and hitting the brakes.

Regarding my highway cruising speed, the average speed on the highway seems to be an insane 80 mph. Anything below 65 mph means I get tons of pissed off drivers swerving around me, honking horns, and flippin' birds, which leads to more stress than it's worth to me. I could get away with slower speed in the rightmost lane, but then I have to deal with braking and re-accelerating for people merging on from ramps, which likely negates any efficiency savings from the lower speed.

Edit/Aside: When my wife and I travel by car for a weekend away, we do usually cruise at 55-60 mph and my highway-only mpg jumps up to a whopping 46 mpg. We did a series of tests during one trip and found that to be the ideal speed range for our car given a flat grade and not much wind.

(edited by samoflange on 17.6.11 1117)

(edited by samoflange on 17.6.11 1119)

Lloyd: When I met Mary, I got that old fashioned romantic feeling, where I'd do anything to bone her.
Harry: That's a special feeling.
Zeruel
Thirty Millionth Hit
Moderator








Since: 2.1.02
From: The Silver Spring in the Land of Mary.

Since last post: 3 days
Last activity: 9 hours
#5 Posted on | Instant Rating: 5.03
    Originally posted by samoflange

    I work earlier hours than most commuters, so there isn't too much traffic. So, I maybe hit 3 red lights out of those 7, and most of those I can see from way ahead and will coast instead of maintaining speed all the way up and hitting the brakes.


Ahh, ok. It really is a wash. You're saving a little bit of gas, but I'd still go with route 2 but that is my own personal preference. I hate stop and go. If nothing else, it will reduce SLIGHTLY on break wear, but we're probably talking about amounts too small to measure in the short-term.




    Edit/Aside: When my wife and I travel by car for a weekend away, we do usually cruise at 55-60 mph and my highway-only mpg jumps up to a whopping 46 mpg. We did a series of tests during one trip and found that to be the ideal speed range for our car given a flat grade and not much wind.

    (edited by samoflange on 17.6.11 1117)

    (edited by samoflange on 17.6.11 1119)


Every car has that sweet spot, where at a flat grade with a constant speed, they get the most MPG.

My car is weird. I have a U shaped sweet spot, so to speak. I get great MPG at 45ish in 5th, and also in 75 in 5th. At 60, my MPG on my dash computer stays even or even drops a tenth of a MPG. The farther I stay away from 60, either high or low, I get better MPG.

My 2 tanks ago, I was doing mostly beltway driving as I drove my roommate and a friend to National airport and back. Other than that, I was doing the same driving to work and back. I was averaging 75 on the beltway and the GW parkway (and we waved to Stan Smith as we passed the CIA) but I usually cruise 60 on the new toll road highway I use.

That tank was 330.7 miles on 14.35 gallons for 23.05 MPG. The tank before and after were 22.30 and 21.97 MPG respectively. The last tank, before I hit the highway, I was on my local roads going 45 after filling up, I averaged 25 MPG after about 14 miles of driving (7 each way). Obviously, I didn't keep the average up, but I really need to test it out sometime.

Sorry for the rambling in each post. I just love talking cars now that I have one worth talking about.



-- 2006 Time magazine Person of the Year --
Fuelly
-- July 2009 Ordained Reverend --
DrDirt
Banger








Since: 8.10.03
From: flyover country

Since last post: 3 days
Last activity: 1 day
#6 Posted on | Instant Rating: 9.71
Theoretically, your repairs should be less with fewer potential stops but this is such a small distance and you seem like an intelligent driver it is probably a wash. There might be a slight edge to going 65 just to let the vehicle run.

I drove 50 miles each way for six years and one route was 65 mph almost the whole way and the other 55 mph most of the way. I would typically take the faster route in the morning and the slower route through several little towns on the way home. Just broke things up and let me detox from work.

(edited by DrDirt on 17.6.11 1227)


Perception is reality
samoflange
Lap cheong








Since: 22.2.04
From: Cambridge, MA

Since last post: 281 days
Last activity: 274 days
#7 Posted on | Instant Rating: 8.62
Thanks for the info. I asked the same question of my dad, who, like all dads, knows way more about cars than I do. He said that I should just mix it up. Driving on slow roads is more relaxing to me, and the highway is less busy in the morning, so I've been taking the highway on the way to work and the backroads home.



Lloyd: When I met Mary, I got that old fashioned romantic feeling, where I'd do anything to bone her.
Harry: That's a special feeling.
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