Yesterday, our Senior Editor Jason Cammisa related a fantastic tale: The luxury sedan that beat the Prius in a real-world MPG battle. Now, go deeper as Cammisa tells the surprisingly interesting story behind the intriguing result.

I can't decide what's more annoying about the Toyota Prius: the people who buy it, or the fact that the car does such a good job of delivering ridiculous

gas mileage. Seriously—the harder you beat it, the less gas the damn thing uses. It's infuriating.

Discounting the fact that the World's Worst Drivers Club somehow managed to get 75 percent off pricing on the purchase of a Prius, and evaluating the car on its

actual merits, the hybrid nerd-machine is an amazing piece of engineering. Its sole mission is fuel economy—so it's not particularly fun to drive, but it's

not a bad car, either. Yes, it's ugly. But it's amazingly inexpensive given what it is, reasonably comfortable, impressively roomy, and even surprisingly

lightweight. And it's actually more than quick enough to keep up with traffic.

Not so you'd notice, given how painfully slowly its semi-conscious buyers drive the damn things. There's nothing more I'd like to do than to annoy these

people back—and the perfect way is to make them feel like they're wasting their life inside a Prius when they could be getting the same fuel mileage while

being pampered in a Mercedes.

The new Mercedes-Benz E250 Bluetec is a proper mid-size luxury sedan. It makes no sacrifice to fuel economy, really, but it gets an EPA-rated 45 mpg on the

highway. That's spitting distance from the best-performer Prius's 48—and in our experience, diesels usually outperform their EPA numbers, while hybrids

underperform in the real world. So my hypothesis was that, when driven like a normal person, the Mercedes had a good chance of beating the Prius. Wouldn't

that be something?

To test the theory, I got a rear-wheel-drive Mercedes E250 Bluetec (4MATIC all-wheel-drive is an option) and a loaded Prius Five. (This is, confusingly,

the model name for the loaded Prius, and not a Prius v, which is an entirely different vehicle.)

I planned out a 430-mile route that both cars should be able to make without refueling, and chose a mix of Interstate and rural back roads that passed

through small towns. To minimize the effects of the constant westerly wind we have on the West Coast, I chose a route that's as close to a circle as

possible. And to be fair to the Prius, I eliminated any of California's enormous elevation changes. The route started and ended at sea level, climbing once

to 1800 feet, twice to 1000, and remained free of very steep climbs.

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I roped my friend Mike into helping me, and the first thing we did was warm up the cars by driving them for a half-hour. We then set the tires to the

manufacturer-recommended pressures before filling both cars with fuel. Measuring actual fuel used is much more difficult than you'd think—in all honesty, it's

nearly impossible—so we did our best to minimize any chance of error. That meant filling each car to the top of its filler neck and then weighing the cars.

We'd weigh them again at the end of the test to ensure there was no discrepancy in weight (caused, for example, by a one-gallon air bubble in a filler

neck.)

We set out with only two rules: don't get separated, and drive like a reasonable human being. That meant we should keep up with traffic—no hypermiling—and

with each other. Every 20 miles, we would swap positions so that neither car was in the lead more often. And every 40 miles, we would swap drivers. This, we

hoped, would minimize the effects of our differing driving styles.

In constant radio contact, we would report our trip computer's displayed odometer reading and average MPG every 10 miles. More than anything, just to

stress each other out.

THE TRIP

The trip departs from Brisbane, California, just south of San Francisco, and we merge right onto the highway. Heading south with traffic at about 80 mph, the trip

computers are in lockstep, both showing 42.8 mpg at the 50-mile mark. As we begin to climb to the highest elevation on the route, the Mercedes starts to

pull a big advantage.

And by big, I mean 0.5 mpg. Nearing the top of the hill, the Benz shows 40.6 mpg to the Prius's 40.1. I radio Mike when, at the 68-mile mark, the Mercedes

downshifts out of top gear for the first time in the test. The engine is turning all of 1800 rpm. "Wow, I still can't hear this engine. How's the Prius

doing?"

From the car in front of me, via radio: "The Prius is about to code."

Laughing, I ask, "What do you mean?"

"Cardiac arrest. My foot's on the floor. Has been for miles. Engine's screaming, some fan in the back seat just kicked on. But hey, we're just keeping up

with traffic."

At that point, the Mercedes shifts down another gear, into fifth, and the tachometer finally meanders past 2000 rpm. I still can't hear the engine. What a

difference torque makes.

When we pull into the first town at 84 miles, we're disappointed that the Mercedes's auto stop/start doesn't always shut the engine off at lights. Perhaps

the A/C is at fault—we left it on in both cars for the sake of fairness—but it's very disconcerting given that, in traffic, the Prius's engine is off more often

than it's on.

By the 110-mile mark, we've cruised through a few towns, where the hybrid system's advantage pays dividends, and the Prius has pulled a massive 1.0-mpg

displayed advantage—44.6 versus the Mercedes's 43.6 mpg.

Mike and I are both impressed that the two cars' odometers are reading so closely—they're within 0.1 mile at the 120-mile marker. Equally as impressive,

for the Prius, is that they're also able to maintain the same brisk pace on a twisty section of road. There's little doubt that the Mercedes would outrun

the Toyota in an all-out back-road race, but the cars are similar in terms of overall grip. And the Prius exhibits pretty commendable body control over the

bumps. Anyone driving this car at wheelchair speeds has no reason to do so.

At 150 miles, I boast over the radio that the Prius's computer is showing 313 miles of remaining fuel range. Mike radios back, "Uh, the Mercedes can do

another 771 miles. Loser."

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Somewhere around the 200-mile mark, we find ourselves on a deserted stretch of perfectly straight road with no one around. I nudge the Prius up to 90 mph.

Then 100. Then 112. Then 114. Mike announces that the Mercedes speedo is showing 115 mph.

I announce that the Prius won't go any faster.

Mike announces that the Mercedes, yet again, hasn't bothered to downshift out of top gear. And the unbelievably quiet diesel still hasn't once spun past

2500 rpm. I announce that I can barely hear him over the wind noise, the screaming engine noise, and what sounds like an Electrolux in the back seat. (It's

the battery pack's cooling fan, which has kicked on again.) Hitting a buck-ten is, for the record, within the realm of what "reasonable people" would do

driving on this abandoned road. But we don't expect most people to stay at a their Prius's top speed for long, so the fun lasts only a few short seconds.

And so it's back to a reasonable 65 mph. There are a few points on the two-lane roads where we pass slow-moving vehicles. Any time the Mercedes is in

front, there's the invariable call from the Prius: "Slow down, Speed Racer, I can't keep up." And then the response, "Ugh, fine. Still in seventh gear, at

like one-quarter throttle."

The difference in accelerative capability between the Prius (0-60 in 10 seconds) and the E250 (0-60 in 7.3 seconds) is far greater than those numbers

suggest, thanks to the diesel's torque. In an outright drag race through the quarter-mile, sure, the Prius is "only" 1.9 seconds behind, and if you have a

look at the 5-60-mph acceleration times, you can see how much the Mercedes's turbo lag gets in the way of instant response. But in the real world, the

difference between the low-revving turbodiesel's 369 lb-ft of torque and the Prius's torque-deprived Atkinson-cycle gas engine feels like 10 times what it

is.

As we head west into the headwind, our hope for a close race starts to fade faster than the daylight. The Prius has been pulling an ever-increasing

advantage. We're both eagle-eyeing the odometers for the 10-mile-interval updates, and each time, the Prius has gained a bigger lead. By the 250-mile mark,

the trip computer shows the Prius winning by a solid 0.6 mpg. I consoled Mike, "These displays are so wildly inaccurate that this is all meaningless. One

of the cars could actually be winning by 3 or 4 mpg."

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What wasn't helping our optimism was that the Mercedes's instantaneous-mpg gauge only goes to 40 mpg. So it's been pegged nearly the whole drive and we

can't see what sort of mileage we're actually getting. Meanwhile, the optimistic Prius has a 100-mpg scale, and it's hovering just below the halfway mark.

At 290 miles, Mike radios from the Prius that he's down to one quarter of a tank. Meanwhile, the E250 still has two-thirds of a tank remaining, a fact that amuses

us both. Until I take a few minutes to look at the map and realize that we're not going to make it.

At this rate, the Prius will run out of gas 50 miles before the planned end of the test. We make an emergency adjustment to the route and cut out

Sacramento entirely, making a beeline for Marin County and, if the range indicator is accurate, having at least a half-gallon of fuel left.

At 391 miles, the Prius's low-fuel light comes on. Which is fine, except that range has dropped to 19 miles and our new, closer finish line is still 20

miles away.

"Worst case, we hop in the Benz and bring the Prius a gallon of gas."

"It'll need more than one gallon. It might need a couple. Range just dropped to 14 miles, 19.6 remaining on the nav." And at 402.3 miles, the Prius's range

drops to zero.

I suggest we keep going, since the range was dropping so much more quickly than the odometer was climbing. My suspicion is that Toyota built this logic in

to help prevent its owners from running the tank dry. The unintended side effect is that Mike's blood pressure has just gone through the roof. He's stuck

in the Prius, as we decide not to do another driver change.

Mike: "The last remaining bar on the fuel gauge has been blinking ever since the light went on. And I swear it's blinking twice as fast now. This thing is

pissed. It wants gas. Now."

"You tell me when you're not comfortable continuing on," I answer. But Mike never gives up. We coast into the gas station in darkness, with 410.4 miles on

the Prius's trip odometer. Its computer is showing 43.3 mpg, 1.1 mpg higher than the Mercedes's 42.8.

But as if to stick its tongue out in defiance, the E250's range indicator says we haven't even used half of its cruising ability: 534 miles remaining. How

insane.

We roll the cars onto the scales at the pump after emptying their cabins of trail-mix wrappers and empty water bottles. And fill their tanks with our backs

to the pump displays so we couldn't see how much was going in.

The Prius goes first. Once we're confident that the tank is at the same level it had been in the morning, we turn around and see only 10.218 gallons on the

pump's display. Talk about infuriating: The tank is rated at 11.9 gallons, meaning the Prius actually had nearly 80 miles of fuel left when its range

indicator dropped to zero. Had the gauge been accurate, we wouldn't have needed to cut the trip short. Demerit points for the Toyota.

Next is the Mercedes. Once the tank is full, we look down at the digital scales, and once again the E250 is precisely 1001 lbs heavier than the Prius. And

then we look at the pump: 10.139 gallons of diesel.

The Mercedes wins, having used 0.079 gallons less.

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0.079 gallons is about 10 fluid ounces. As in, less than a can of soda. Which is, of course, a small enough amount that it's entirely insignificant. Since

the difference is within the margin of error, we can't actually say the Mercedes won. In fairness, the two cars tied.

But that itself is a huge win for the Mercedes. The Prius is a car single-mindedly focused on efficiency. Every part of it, from its shape to its

low-rolling-resistance tires to the hybrid transmission to its blended-regeneration brake system, has been chosen to minimize its consumption of fuel.

The Prius is a tremendously efficient package, too, with a bigger backseat than the E-class and a usable hatchback for cargo. It's reasonably quiet,

quick, and smooth. And it returns unbeatable fuel mileage, even on the open road when the big benefits of its hybrid system are minimized.

Unbeatable fuel mileage, yes, but not unmatchable. The Mercedes E250 Bluetec returned effectively the same mileage as the Prius, and yet it's not focused

on fuel economy at all. It's a big (15.7 inches longer than the Prius), massively overweight rear-wheel-drive luxury sedan. Save perhaps carrying cargo and

rear-seat passengers—and pissing off everyone else on the road—it does everything better than the Toyota. It's different-league fast, relaxing,

comfortable, and luxurious.

To us, all that is more than enough to easily break the tie. On the open road, the Mercedes E250 Bluetec is the winner of our fuel-economy challenge.

Feel free to tell that jerk in a Prius blocking the left lane that he should have bought a Mercedes. If you want to really piss him off, remind him that it

is, in fact, easy being green. And he shoulda bought a diesel Benz.

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