Which pedal wastes more gas?

Well the brake pedal isn't going to use any gas, but I know what you're getting at. The more often, and harder you brake, the more you are going to need to use the gas pedal to make up for it. The most efficient would probably be if you didn't use the brake pedal at all and just coast to slow down. While you're coasting, you're not using much fuel. So you are making the most use of the stored energy in your momentum. It's better to use that kinetic energy to move the vehicle rather than heat up the brake rotors.

A couple years ago, I came up with a method to test this. Start with a car with an electronic fuel usage system. Garmin actually makes (made?) one that plugs into the car's OBDII port. I am sure there are smart phone apps these days that can interface with the car and the right adaptor. An electronic setup would be a lot more accurate than a graduated cylinder. Faster too. Plus we know the MB have access to the equipment.

My though was a long straight track you have a measured 1/4 mile. You could use a drag strip here, but I was just planing a back country road. From a complete stop, you accelerate to 65 MPH and then hold that speed with cruse control and come to a control stop after 1/4 mile. You can then get the total fuel usage for the test with your measuring device. Each test you vary your acceleration. Start with 10% throttle, then 25%, 33%, 50%, 66%, 75%, and then full throttle. I was planing on just using wooden blocks under the gas pedal to limit travel of the pedal. I would just take out one block each test to allow for more pedal travel. Each test I would press the pedal to the block.

I never got around to actually testing it, but that was my thought process.

Driving tips to avoid wasted gas.
"Roll through".
You should approach a set of lights as if you intend to roll on through when they go green...
This all depends on "Timing", and is better on a set of lights that you know the sequence of?.
So slow down gently with plenty of space, dropping a cog as required, dont scream up to the lights and brake at last moment, slow down well in advance of the lights. On Modern cars and trucks, you have over-run protection that stops the flow of fuel as you slow down on the engine, you want to use as much of that as possible for as long as possible, as all the length of road you use doing that is "Free", so, having to brake is using less of that free road length?...

It is advisable to rest your foot on the brake pedal just enough to illuminate the brake lights to warn the vehicles behind you are slowing down.
It is advisable that you also PLAN to stop, because lights never behave the way YOU want them to, so dont get upset when you have to stop... just enjoy the ones where you dont have to stop.
Also, if the lights change in short distance, and you cant do anything else but stop?... well just ignore above and stop as required.

If you stop, you have to start again from standstill, obviously, but of you are still doing 15mph, then that first acceleration to 15mph is also "free"?... so try and get that as often as possible.
(On any road above 30mph) You should plant to approach any set of lights by slowing to 10mph UNDER the posted limit a good way ahead of those lights anyway, drop 5mph on a 30 limit, a good deal ahead of the lights, even if they are on green.... green is the most dangerous, as "Its my right of way" is a [bad] excuse for an epitaph.... and those lights will never stay green as long as you think they will.

Obviously but to make it plain, you must stop if the lights are on red.... you dont just roll through a red light do you?...
You must also make damn sure you check BOTH WAYS for red-light jumpers in the opposing directions.

This also applies to corners, and again, better on corners you can see and plan ahead for, or know.
Intend to enter the corner at the speed you will leave the corner, and dont brake, just slow down gently before the corner using Engine braking and over-run protection for free road space again, to the speed you require.
Use brake as necessary, of course, but try to use the engine more.

Gentle acceleration.
If you have a light vehicle with no load, do you absolutely need 1st gear?.. (Low powered cars to ignore this... if you drive a no-so-smart, do you need a tow start?.)
I have done whole trips not bothering 1st gear at all, being on the flat and no load, I dont need it?.
Facing downhill with an empty car, I can pull away nicely in 2nd... then swap directly to 4th, or 5th even.
If you can skip a gear, go ahead, do so.
And I realise you cant do that in an automatic.
But short-shifting, when you dont need all the engine power, gets you to a higher gear and less fuel use earlier.

Remember you aint a rolling road block. (Again for not-so-smart drivers...)
Dont do the "Granny race start" where your still not exceeding 5mph after 100 yds if you are in rush-hour traffic on a very busy road.
Its not wise winding up a whole queue of traffic for no good reason, so do try to maintain "Reasonable progress"

Plan trips ahead.
If you set off early, you know you have plenty of time, and can relax a lot better....
Being late always makes you tense anyway, so adopt the "Get there when you get there" plan, dont be rushed, and try to be early starting...
If you get held up, most reasonable people will understand.
Those that dont?.. are they worth bothering about?...

Passengers.
Pick yours wisely, and educate them.
First one that says "Cant you hurry up a bit" should get the response "Do you want to walk?..", like you mean it?..

Do NOT let anyone else "drive" you whilst you are in the seat... its YOUR vehicle, YOU are driving, if they get agitated, stop....

I have thrown people out of the vehicle for trying to mess with my driving.
I WILL do it again at some point, I am sure, because I knows people, and just when I aint expecting it, I will get a nonce as a passenger.

Get on the internets and search "Hyper-miling" duckduckgo.com/?q=hypermile&t=ffab
There are a dedicated bunch out there who WILL get every last benefit out of their pint of fuel.
But remember if they advocate "Coasting", its illegal...
Knocking the car out of gear, you miss the over-run free fuel to start with, and not being in gear is "Not being in proper control of the vehicle"... (UK law and other countries)



In addition to above ideas...

Go back to the idea they used with a weighed tank of fuel.
Put a known quantity of fuel that exceeds the requirement in two cars, set one of "gently" and set one off "In a hurry", to the same destination... include a length of "freeway"...
Neither car must break any law or exceed any posted limit, of course

Separate the freeway part as required, one vehicle does 50mph where available, one does the posted limit, again where available (traffic allowing). (This test for the 55mph "barrier" of fuel efficiency)

At the end of each test, weigh the remaining fuel.

My Knowledge states that the car "In a hurry" WILL consume more fuel.

Of course aerodynamics of separate cars change, but, an 'industry standard' assumes most vehicles will see most benefit from fuel efficiency at a average 55mph (maximum... about....) road speed.
It may vary from 55 to 58 dependant on car/load/headwind/etc.

Aero drag goes up with speed. IIRC the drag at 100mph is about four times that at 50mph. As for which pedal can affect gas mileage the most, I'd say the throttle has more influence. There's probably enough material already done on mythbusters to support this stuff.

If SR racing was here, I think he could give the absolutes, but, isnt it that drag goes up by 4X the increase in speed?...

Wiki has pages of the stuff, I dont know exactly what I am looking for, but, as speed increases, drag increases something like four-fold on an average vehicle, above a certain speed, and I think thats about 30-40 mph?..
So being in a higher gear and at the "Optimum" efficiency of an engine is lower than its top speed, of course, and it "Averages out" in an average car at about 50 to 60 mph... on average.

The CD of cars is about 1.5 to 1.7 on an average...

Industry wide, they have designed cars with "Just enough" aerodynamics to make them usable whilst economical to make, with a large enough interior, to manage an average 55mph ultimate fuel efficiency (With wind-speed of zero on the flat etc...)

You can get better, but you sacrifice body size, to give less drag.

Its all a compromise.

If you want LARGE vehicles with plenty of cargo space, you sacrifice speed, or fuel efficiency, or power, or all of them.

...But that is the engine at its highest efficiency.
You have more than an engine to a car?...
As the drag increases, the engine efficiency decreases PLUS the rest of the car makes the whole car's efficiency decrease.