Gas savings from driving slower

Tying a mattress and box springs to the top of the Prius probably wouldn't be the best, aerodynamically speaking.

 

This is a great article with some solid information.
At my job, I was recently made fun of for sorting through the trash can to pick out aluminum cans. This sparked a huge discussion about carbon footprints and improving each person's impact. Very few people here know I drive a Prius, so I simply stated that by driving slower you could save gas. NO ONE believed me. So the timing of this article is perfect.

Thanks!

somechic

 

FFS! They obviously don't know much about physics if they didn't believe you. :doh:

 

I drive 65% freeway on my combined (25 miles each way) 50 mile commute each day. I'll drive between 75-85mph during a big chunk of this freeway drive. My last tank that I filled up a few hous ago showed 52.5 MPG and 508.5 miles on the tank. I haven't had a tank in months under 50mpg. Perhaps my '08 Prius is a freak of nature? Yeah, I'm 10% less than your best tank but I'm gettin' there much faster. It sure helps that in AZ it's been a solid 80-85 degrees out.

 

Maybe there is no atmosphere where they live. Driving in a vacuum helps with drag.

Tom

 

Ok, let me get this straight. Your one way commute is a total of 25 miles.
65% of that, or 16.25 miles is on the freeway.
You drive "between 75-85 mph during a big chunk of the freeway drive"

So I'll use 80mph as an average, and I'll even give you the benefit of assuming that "a big chunk" means the entire distance.

At 55 mph, it will take you 17 minutes and 40 seconds to drive that 16.25 miles. At 80 mph it will take you 12 minutes and 11 seconds to drive that same distance. This means that if you actually average 80 mph for the entire freeway drive, you will get there 5 minutes and 29 seconds faster. I suppose I could consider 5-and-a-half minutes "much faster", but I prefer to leave home 10 minutes earlier, and avoid the stress of trying to beat the clock. I can drive 55 mph, and still have 4-and-a-half minutes "in the bank" in case of unexpected traffic issues. Meanwhile you significantly increase your risk of eventually receiving a speeding ticket as well as increasing your fuel costs over the life of the car.

To each his/her own, and I'm not trying to tell you you are wrong or that you should slow down. That's your choice to make. I just wanted to make sure that you realized that in the best case senario you are refering to 5-and-a-half minutes as "much faster", and that more likely you occasionally have to slow down for traffic or other reasons, so "much faster" is probably even less time than that.

By the way if your 50 mile per day commute is 90% of the miles you put on the car, that works out to a total of 14,444 miles per year. The 10% savings then works out to:

14444 / 52.5 = 275.1 gallons

14444 / 58.0 = 249.0 gallons

275.1 - 249.0 = 26.1 gallons

26.1 gallons at $3.50 per gallon = $91.35

So in comparison, assuming you never get a speeding ticket, you are looking at paying an extra $91.35 per year for the privilege of getting to work about 5 minutes earlier.

 

Of course! I completely forgot about that... actually, Somechic's in Jersey, I think, so they've got loads of atmosphere to plow through there. I'm the one that should be using the "no atmosphere" argument.

 

Nice post Danny.

For me the added 5 minutes would be worth the reduction in stress and more time I have to listen to my books on CD.

I've done the "Nascar commute" long enough to realize it's not worth the risks or the money. I'm getting older now so the idea of blasting through gaps in traffic in the Corvette just doesn't hold the same appeal it once did.

 

Danny,

When I saw the comment about getting to work faster, I was all ready to post about it and do, basically, the same math you just did. Nicely done!

F8L - I don't like driving 55 mph when everyone else is flying by 15-25 mph faster than myself, but I'm trying to get my best fuel economy, so I suck it up. One day, I'll get my Prius and be posting in the "I beat the EPA" section too, but with the new EPA estimates, it won't be nearly as sexy as it used to be.

Funnily enough, when visiting Hawaii, many years ago, the speed limit was 55 mph and everyone drove it (small island, unmarked police cars with radar, etc) and it was easy to drive 55 mph. There is a "psychology" to driving, I'm guessing a pack mentality. If everyone is going 70 mph, there seems to be this urge to also go 70 mph, and likely 75 mph, just so it seems that you are moving up through the pack. I wonder if some grad student somewhere has written that grant proposal to study that aspect of human driving pyschology.

 

I know what you mean but I eventually got over it. The freeway is easy but two-lane roads can be a lil nerve-wracking when people are doing 85 and I'm doing 55.

In the Prius I have a much easier time ignoring the "peer pressure" to speed. When I still had my truck and Vette I would sometimes follow the pack without even noticing it and then I would have to slow down again. The Prius just has a calming effect... The MFD is like a sedative and it seduces you into driving for efficiency.

 

Well my normal commute is about 35 kilometres each way across town and I get 4.2 to 4.4 L/100km. I leave to go to Alice Springs with my family next week and I will be driving at the speed limit, that is 110km/h most of the journey. I expect I'll be using 5.2 to 5.5 L/100km on this trip as I did on a previous, shorter country trip. If I drove at 80 to 90 km/h I wouldn't have much time on my holiday to do much but drive except when I am stopping in a town for 2 nights or more, and I'll also get very bored.

I will be happy with 5.2 L/100km rather than the 11 L/100km I would get in our RAV4. I have the Prius because it will move me and when requires my family comfortably using less fuel, polluting less and without compromising speed or comfort.

This will be a journey of about 3600 km and lets assume if I drove at 80km/h I would use 4.3L/100km.

In the Prius at 110km/h @ 5.2 L/100km I'll use 187.2 litres of petrol over 32.72 hours.
In the Prius at 80km/h @ 4.3 L/100km I'll use 154.8 litres of petrol over 45 hours.
In the RAV4 at 110km/h @ 11 L/100km I'll use 396 litres of petrol over 32.72 hours.

You can see that just by taking the Prius rather than the RAV4, I save over 200 litres of petrol.
So in my Prius I can spend an extra 12.3 hours of driving and save 32.6 litres of fuel. At about 150c per litre allowing for expensive country fuel that 12+ hours will cost me just under $50. Now I know my time is worth a lot more than $4.06 per hour, how about yours? This isn't just ordinary time either, I'm talking about vacation time, a rare 4 weeks per year.

 

Yes, I'm in Jersey and there's plenty of atmosphere here. I think people just like driving fast and/or carelessly. I am the worse passenger in other people's cars because of this.

 

You know, now that gas is more expensive, I've noticed again that people are driving somewhat slower. There's always the odd nutter out there in his F350 Supercab, trying to win a Grand Prix, but for the most part people are driving less aggressively.