I think one of the problems is that the EPA wants to represent fuel economy as just two numbers. That's not a lot of information. I'm thinking we should have a lot more info on the window sticker.My ideal sticker would have three sections: city estimates, highway estimates, and general info. For the highway section there should be at least 3 numbers listed: MPG for a constant 50 mph, 60 mph, and 70 mph.

For the general info section, there should be at least two numbers: one for the approximate percentage hit from using a/c and one from using the rear defroster.

Finally we have the city section. This would be much more difficult to figure out as it's not quite as easy as getting up to speed and clicking the cruise control button. We could have numbers such as an MPG for crawling in a traffic jam or an MPG for low traffic with a stoplight at the end of each city block each with modifiers for aggressive or granny-like driving. There's lots of room here for improvement. Of course you don't want to overload people with too much information, otherwise they end up looking like this ->

I guess the real question to you is would you want to see this information or is this all too much and you prefer it the way it is now with more mathematical massaging done to the numbers?

 

It might be possible to have some cake and eat the rest. Perhaps the two *biggies* could be presented as they are now, with a smaller table indicating estimates under different conditions such as speed, accessories, etc.

Those who just wanted a comparison estimate could use the biggies as they do now. The serious shopper would have to look more closely but would have much additional information on which to base a decision.

 

I think all that information would be too much for most people- they think in averages and don't measure mpg under different conditions or sort it out in chunks as you propose. Consumers probably do as much research before buying a car as they do before they buy anything else in their lives, because it's such a big decision and a relatively large cost. Having that information available at such a level of detail for the people who want it and look up the stats in guides like CR would be great, but in terms of what to put on the sticker for the general consumer browsing a car lot or a fact sheet, it helps to have an index that can be distilled to one or two numbers. It's easy to read, process and remember.

I like your idea of breaking it down by speed, but for my two cents I think that a few temperature slots would help as well. All cars do worse in the cold, but if car companies were trying to be competitive with their numbers, which we all know they do, they might work harder to be better 'cold weather' cars to try to pick up sales in certain areas, which would be a great incentive to improve FE overall. Just a thought.

 

Maybe just allow people to go to the EPA website and define their driving conditions (speed, urban/highway, etc), then they get an estimate.

 

This percentage hit woudl be difficult to calculate, as it would depend on where in the RPM range you are driving. If you're below the efficiency sweet spot, the effect would not be nearlty as pronounced as if you are over it.

I do agree though that steady cruising numbers for 45/60/75 would be nice to see. Another thing that would be interesting to see woudl be a "cold start/short trip" value figuring a cold engine running for only like 3 miles with a few stops mixed in.

Also, I believe that it would be more straightforwrad for cost-benefit to list the fuel economy in fuel consumption rather than fuel mileage, using units such as GPC (gallons/100mi) It's easier to figure the costs to drive cars that burn 3.5gpc or 2gpc than cars that get 28.5mpg or 50mpg, respectively (note: those values are equivalent).

 

As I posted in another thread I think that inverting the numbers gives a more meaningful representation in today's real world situations. Some variables do not apply to everyone. 'Discounting' fuel economy due winter weather driving as is now being proposed is meaningless in FL and SoCal. It does apply to most of the country so there is some justification for using it.

Perhaps a commentary such as:
"Driving in winter weather conditions may decrease your fuel economy up to 20%"

Combined EPA Fuel Economy should be specified as:
"Based on equal parts City and Highway driving. Your Combined Values May Vary"

Fuel Economy should ( IMO ) should be stated in terms of Usage:

PRIUS II

Highway Driving: (Gal used/100 mi)
55 mph - 2.0 GPC
65 mph - 2.2 GPC
75 mph - 2.6 GPC

City Driving: (Gal used/100 mi)
2.4 - 1.7 GPC
Conditions vary significantly

 

I like this idea...that way if they are really interested, they can look it up and if not, it would be similar to now.