Easy way to explain why Prius gets higher City MPG than highway

here's my 2cents...

I get 50mpg on my daily commute, 5% freeway 95% local (50mph). When I go up to LA from SD, I get 60mpg (60mph) and 52mpg (75mph) I had to rush to LAX once and I was going 80mph half the time. The trip ended up being 50mpg. I do not understand how pple are getting below 45mpg on their prius. Maybe they are AGiii impersonators.

I notice that when I am in LA stop and go traffic, I can get about 70mpg. I don't know how the finer points of gliding. I would like to up my daily average from 50 to 60mpg. :/

*mpg are calculated on a spreadsheet based on Trip A and MFD.

 

<div class='quotetop'>QUOTE(ACORNBLUES @ Aug 2 2007, 02:50 PM) [snapback]489507[/snapback]</div>

Because their commute is like mine :lol:
(1) high-speed highway (75mph like most Californian drivers) and short distance (<10miles)
(2) congested local traffiic and impatient drivers forcing you to catch up with other jack-rabbits
I average 45mpg on my 17mile commute in bay area (50%/50% highway/local)
Recently I found a local route with 40-50mph limit and long separated red lights,
I am now getting 49mpg (same distance, but 25%/75 highway/local now).

As someone put it, if you could find a long stretch of local uncongested route (30-50mph) with long separated red lights/stop signs, your mpg would be very high (50+mpg easily), provided that the trip is also longer than 5 miles.

 

<div class='quotetop'>QUOTE(wkramer @ Aug 2 2007, 01:10 PM) [snapback]489352[/snapback]</div>

Since you mentioned that you hit all those lights before you get to the highway, I wondered if you were looking at the MPG from the beginning of your trip, which also happens to be 'city' driving, vs. highway driving after the ICE has warmed-up. The MPG figures I quoted in an earlier post did not include the initial miles before the ICE has warmed-up; I got them by hitting the MFD Reset at the start of different driving modes (I calculate my overall MPG the old-fashioned way, so I don't worry about losing the history.)

My MPG for the first 5 minutes on the MFD always sucks... if I get over 25 I'm thrilled. It's often much lower. I just got gas today, and the tank average was 52.5, so that initial warm-up does take its toll on the overall mileage. I wonder if some of the folks who are getting dismal MPG numbers are doing many short trips, so that a large percentage of their driving is in that pre-warmup stage. Fortunately (for my MPG anyway) my regular trips are 35-60 miles.

 

funny how i get better mileage on the freeway. i get about 53/54 mpg driving 70 mph on the 405 and the 5 freeway from los angeles to san diego. while i get about 47-50 in the city in los angeles. weird

 

<div class='quotetop'>QUOTE(Bob64 @ Aug 1 2007, 08:27 PM) [snapback]488992[/snapback]</div>

You all are a little too hard on bendial!

The fact of the matter is Bay Area especially dense hilly bay area with short commutes is not P&G territory, so "city", "urban" whatever you want to call it doesn't really apply. We have the exact opposite of the OP's question, city is low mpg and highway is high mpg.

In SF for instance you would be hard pressed to find a commute that is more then 7 miles! The ICE isn't even warmed up. Awhile back a PC.com poster said we should just get bikes or walk, true in theory, but 45-65 F plus wind kind of makes you think twice.

Anywho, ask a few more questions of bendial before you poke at his dismal numbers. I think you'lll find there are like four different types of driving in the US if not every country: urban, suburban, rural and dense population centers with short commutes.

Back on topic, I agree with those who basically said the short answer is that the reason why (in a "suburban-rural" area) Prius is higher in the 'city' is because the engine shuts off when not needed.

 

A material from Toyota says Prius city fuel economy is almost 100% gain from a conventional vehicle.

The areas are...
30% gain: idling stop/engine off coasting (almost no gain on highway)
30% gain: ICE runs most efficient torque and rpm combination
25% gain: regeneration (almost no gain on highway)
15% gain: Atkinson cycle engine

So, Prius gets about 45% gain from a conventional vehicle on highway.

Ken@Japan

 

<div class='quotetop'>QUOTE(etyler88 @ Aug 1 2007, 03:36 PM) [snapback]488829[/snapback]</div>

I thought I was the only one who this happens to. =\

<div class='quotetop'>QUOTE(Bendial @ Aug 1 2007, 03:53 PM) [snapback]488846[/snapback]</div>

The reader shows different though. I can't accelerate at all without the power switching straight to the engine. Most of the time, I simply let go of the gas and my car jerks.

 

<div class='quotetop'>QUOTE(ken1784 @ Aug 3 2007, 03:00 AM) [snapback]489833[/snapback]</div>

Ken, that's great information (like you always have!). I'm not sure I've seen it before. Is the material available online for linking? I'd like to be able to cite the original source if I use this in other discussions.

 

<div class='quotetop'>QUOTE(JimboK @ Aug 3 2007, 10:25 PM) [snapback]489894[/snapback]</div>

Thank you!
Me neither. <_<

No, there is no online information. It was shown on the New Car Features material for the NHW-10 original Prius.
Actually, it was a very small chart and there was no percent value shown.
The percent reading is my original.
Please do not be so serious about the percent values which is not official from Toyota.

Sorry, but there is no online info.
However, these gain areas match our observations, city mleage is better than highway which is typical on HSD system.

Ken@Japan

 

The way I try to explain how the Prius gets good mpg is that most cars burn petrol all the time just at differing amounts, the Prius if driven economically only runs the engine 50% of the time. So if you drive the car and get 30mpg, the 50% of the time you are not using any fuel means you will actually get 60mpg.
I know it is not quite as simple as that but it is a quick way to explain which I find people understand.

 

Tell them it's the dilithium crystals B)

 

<div class='quotetop'>QUOTE(GeoDosch @ Aug 14 2007, 07:11 AM) [snapback]495303[/snapback]</div>

Didn't you hear? We replaced those with Folgers crystals...

 

Seawolf,

Your last description is very good.

The main reason the Prius gets better mileage in the city is because there is less air drag.

If you had say, an electric car that regenerated all of the energy used in braking at 100% efficiency, you would get better mileaage the slower you went because the only variable in efficiency is the aerodynamic drag.

The people that say you get better mileage in the city because you use the electric motor more often are flat out wrong. All of the energy used by the motor is generated by the engine. All of it. 100% There is no free mpg from using the electric motor!

Another important factor in the EPA numbers is this. The numbers posted on the window stickers are not the actual numbers the vehicle got in the test protocol. The actual highway number is reduced 22% from the test number and the city number is reduced by 10%. So the numbers look like this;

WDO Sticker Tested Number
City 60mpg 66.6mpg
HWY 51mpg 65.4mpg

So, during the actual testing of the Prius, the city mpg is only 1mpg better than the highway mpg. So, the prius gained mpg in the city test because of reduced aerodynamic drag, but since storage process for the regenerative braking is not 100% efficient, the city number is only slightly better than the highway number.

Here is a link that describes the 22% and 10% reduction in the EPA numbers.

http://www.epa.gov/fueleconomy/420f06009.htm

A more accurate way to from the city/highway mpg question would be this. Why do most cars get better mileage on the highway? There is more aerodynamic drag on the highway, so why do they get better mileage. The answers are, in city driving most cars; loose energy to heat from braking, waste energy while idling, operate the engine at a less efficient load range.

 

<div class='quotetop'>QUOTE(usbseawolf2000 @ Aug 1 2007, 10:28 PM) [snapback]488821[/snapback]</div>

"In the city, your car spends half the time burning gas just to keep the engine idling while you're coasting, braking, going downhill, stopped, and going slow.
The Prius doesn't."

 

<div class='quotetop'>QUOTE(Winston @ Aug 14 2007, 12:53 PM) [snapback]495398[/snapback]</div>

Yes, that is the mantra of the anti-hybrid camp. And every time a Prius owner repeats it, Rush Limbaugh smiles. Maybe you're thinking that Toyota created this very efficient car, and then for some inexplicable reason (perhaps they don't have a good grasp on the laws of physics) installed an electric motor that really doesn't gain you anything. :huh:

<div class='quotetop'>QUOTE(Winston @ Aug 14 2007, 12:53 PM) [snapback]495398[/snapback]</div>

These are all true. But you left out an important aspect about other cars losing energy from braking. Yes, the Prius recaptures most of that. But all that recaptured energy would be of little value if you didn't reuse it by means of the electric motor. So your statement that the electric motor doesn't help get better mileage is missing the whole point of hybrid technology.

 

<div class='quotetop'>QUOTE(Winston @ Aug 14 2007, 12:53 PM) [snapback]495398[/snapback]</div>

<div class='quotetop'>QUOTE(GeoDosch @ Aug 18 2007, 12:29 PM) [snapback]498352[/snapback]</div>

Well, there are elements of truth to Winston's comments. It's true that the sole source of that electricity is the gasoline engine; the hybrid system doesn't magically create new energy. It's also true that involving the battery and electric motors in the process reduces the efficiency potential (versus direct usage) due to the losses during storage, extraction, and usage. However, the electrical system improves the overall mileage by capturing energy that would otherwise be wasted as heat and then using it to reduce the load on the engine. It can also improve mileage by allowing the engine to operate at a significantly more efficient level than instantaneous demand requires and capturing any excess energy produced at that load.

It's a simple concept, really. Without the electrical system, you have 100% waste of all energy not consumed immediately by kinetic activity. With the electrical system, some percentage of that energy -- the exact amount is up for debate -- is captured and reapplied later. Capturing and reusing even part of the energy that would otherwise be wasted means a net gain in overall efficiency. That is sometimes oversimplified as "something from nothing," which draws the obvious counter argument, but in reality it is "something instead of nothing."

Back to the original topic...

Indeed, the higher "city" mileage does seem counter-intuitive at first. It's a real testament to just how effective the HSD is at minimizing wasted energy in city conditions. It may also be a tell-tale indicator of how much energy is lost to drag (and perhaps load inefficiencies?) at highway speeds.

- Justifyd

 

<div class='quotetop'>QUOTE(Fred H @ Aug 18 2007, 08:13 AM) [snapback]498325[/snapback]</div>

This is the net simple explanation for the superior city mileage of the Prius. The EPA city mileage cycle specifies a certain amount of time where the vehicle is stopped. When the Prius' does not need the ICE, it shuts it off. Non-hybrids do not shut the ICE off while the vehicle is stopped or otherwise does not need it (coasting for example). There is an additional explanation for the contribution of the battery to mileage, but that tends to require a deeper level of understanding. Stick to the part about shutting the ICE off when it is not needed. Everyone can get that - even Oxycontin addicts.