Highway better than City - why?

I have the same model, 2003 NHW11 Prius and the key is to understand the control laws. In particular, transitions through 42 MPH are a mileage killer. It is OK to stay say 3-4 mph below or 3-4 mph above but don't transit 42 mph if you can help it. You also need to understand the warm-up cycle.

Below 42 mph, the car will efficiency cycle between gas and electric power and a warmed-up, S3/S4 state Prius will excel. Above 42 mph, the car will efficiently augment engine power and again, your mileage will excel even though the engine must run at all times. It is the transition between these two states that boluxes up the mileage:


Warm-up is important too, especially the transition to S3/S4 at a stop. After the engine coolant reaches 70C, you need to come to a complete stop and let the ICE 'auto-shut.' Now sometimes, this can be a little tricky if the vehicle wants to put a charge on the battery.

My S3/S4 trick is to come to a stop when the coolant reaches 70C (at least 5-6 minutes into the commute) and put the car in "N" for a slow, 10 second count, and then put it in "D". What happens is when in "N," the ICE will naturally idle down to the slowest possible rpm and apparently it takes some "n" seconds at a very low idle to set the "auto-stop" logic. When the car is put into "D," the 'auto-stop' logic does its magic and the ICE stops. Thereafter the car will use electric mode whenever it can. I have pulled into a parking lot with two exits to do this trick knowing that I won't have to worry about following traffic. A brief pause (and letting the rest of the traffic by) is all it takes.

GOOD LUCK!
Bob Wilson

 

It is possible to get very good MPG in sub urban provided that you can
- find a route with <40mph speed limit with very few stops/lights (ICE kicks in at 42mph no matter how gentle you drive)
- accelerate mildly up to 40mph w/o being shot/shouted at by your fellow motorists.

 

I think this is part of the problem. Most of my local driving is in Arlington or DC, which means frequent stop signs, red lights and erratic driving going on all around me. Some routes are better depending on the time of day, e.g., I do better on Braddock Rd (Fairfax County, not Alexandria) or Route 50 inside the beltway if there is not too much traffic on them.

Also the colder weather has a greater effect on the shorter trips than on long ones.

 

Please don't confuse the manual, "P&G" with the built-in control laws that switch between ICE and electric power automatically below 42 mph. Once you are in S3/S4 warm-up mode (pretty important,) all you have to do is avoid transiting 42 mph and just pay attention to traffic and your driving. The usual definition of "P&G" that I've read involves deliberate speed changes and accelerator tricks and is entirely different from just letting the Prius be itself. <grins>

I'm not an advocate of "P&G" although I do use "N" during the warm-up to minimize fuel burn. This has to do with keeping the ICE at a minimum rpm and load as much as possible during warm-up. I don't do accelerator tricks although I've been thinking about an approach.

Bob Wilson

 

If you are charging and discharging, then you are not really doing a pulse and glide; it would be more of an EV and Regen. You want to stay away from charge and discharge cycles for best mileage (obviously).

Tom

 

The EPA tests use the Prius in 'charge and discharge cycles.' If your goal is to achieve EPA test results, drive it as described in the EPA testing protocols. Since the EPA reduces their results by 10%, it is fairly easy to exceed EPA results. For better results, eliminate those parts of the tests that cause higher fuel consumption, like the start-and-stop cycles in the highway test.

Bob Wilson

 

most people get worse mileage in city driving simply because it takes a lot more patience, understanding and concentration to get good mileage.

you already know the answer as to why you get better mileage... "with almost no stops"

that is why. accelerating one time is enough to lower your average over the next several miles... do it every 5 minutes, and you will get only average mileage.

that is why in very heavy traffic, the Prius gets the worst mileage. you would think that averaging 15 mph would get you great mileage, but i have averaged as low as 30 mpg in stop and go...but that is because of the constant acceleration and the less than 3% energy recapture from regen

to get the best mileage, drive 35 mph with no stops... but that is a very difficult route to find... as most have discovered, your best bet is a county road at 50 mph...there you can go several miles between stops and the reason your mileage soars has less to do with velocity than it does with the change in velocity or acceleration/deceleration.

 

The original EPA tests were developed in the 70s well before there were any hybrids. The additional tests aren't geared to any specific car type either. They measure unburned hydrocarbons out the tailpipe on very specific driving cycles and then fudge... err adjust the numbers downwards. See How Vehicles Are Tested and Fuel Economy Test Schedules.

Beating the EPA - The Why’s and how to Hypermile. - CleanMPG Forums and Toyota's Prius-I, reaching for the hypermiler in all of us. - CleanMPG Forums should be helpful. I haven't read the latter in detail since I've read the one for my gen of Prius.

 

My highway mileage is always better than city. The area I live in has no idea about synchronizing lights that are just a few blocks apart...While my gas mileage commuting (mostly freeway/expressway style driving) is always over 50mpg, 57 or 58mpg in the summer, I can't do that around town, even though my car is warmed up. I am always accelerating then stopping shortly after that, which drives me crazy, but nobody else seems to mind.

-Roger

 

The 42 mph barrier clearly exists. Prius never achieves more than 100 mpg above 42 mph.
Japanese hypermilers records are always done below 42 mph.
World record distance on a single tank for a Prius II - Japan - July 4 - Aug 16, 2006 - CleanMPG Forums

Also, we see no or very few regeneration marks on their MFD, which means they do less charging and discharging.

Ken@Japan

 

Question regarding the 42 mph barrier: When I was driving around yesterday, I was able to glide (with no arrows on the screen) up to about 48 mph. Any idea why that's possible?

 

The energy screen is not an engine status screen. It just shows us the energy flow.
The screen sometimes lies, such as warming up, S3a idling, above 42 mph spinning and etc...

Ken@Japan

 

Thank you Ken,

What you've suggested is the optimum distance profile is:

1. maximum ICE efficient operation - split between motion and battery efficient charge
2. efficient battery propulsion - avoid converting momentum into battery charge and excessive current drain

With what we know about Prius performance, we should be able to develop a profile for the optimum driving profile given any route of known distance and altitude change. The key is understanding the route altitude profile to optimize performance. Some mild upgrades are desirable but long level or shallow downgrades are going to be the key.

Bob Wilson

 

Right, no arrows only means no energy flow. You can see no arrows on the interstate at 65 (and higher I'm sure) with CC on if the slope is exactly right to maintain your speed with no regen braking and no energy added in from the ICE or electric motor. The ICE WILL be spinning, without using gas, if you see it over 42 MPH.

 

i still contend that no arrows only means energy flow below a detectable level or below the threshold to display change

i have seen no arrows many times on freeway but still registering 400 mpg on scangauge. so that means someone somewhere is lying.

many people report doing no arrow driving but still seeing their charge level reduced. granted, accessories do use some power, i sincerely doubt that it would be at a level that would cause you to lose a bar of charge in under 20 mins. (i have sat in place with no AC for 30 mins with radio on and never lost a bar. granted, not driving i m sure reduces power needs for the several onboard computers...)

 

Yes, the scangauge is also lying.
CleanMPG reviews the ScanGauge II. - CleanMPG Forums
"Another issue has to do with Fuel Cut. The ScanGauge II has no way to tell if the ICE is in Fuel Cut or if the car is at speed running at idle as you would in a NICE-On. Although the FE calculated and shown is very high under this condition (between 130 and 250 MPG depending on speed and ICE size), fuel is still shown being consumed when it is not thus causing an ever increasing error to build in. If you were the type to decelerate in Fuel Cut with ICE-Braking vs. FAS’ing in a very hilly or mountainous area, this error could degrade the displayed FE accuracy sharply. This is no fault of the ScanGauge II given the OBD-II protocol does not have a Fuel Cut parameter for the ScanGauge II to use for determining when you may or may not be in Fuel Cut. It is however an issue that some owners may have to live with depending on their commutes terrain."

Ken@Japan