Jetta Diesel Tops Prius in Fuel-Economy Marathon... NOT!

Lets use percentages:
58.67% higher fuel cost
47.52% more CO2 emissions
CARB emissions: off the chart.

Diesels are getting better, and we are all benefit because one way or another someone is going to burn that fuel. But simply from my environmentalist perspective I don't find a diesel car compelling compared to a Prius. Maybe cracking diesel into hydrogen is a cleaner use ?

 

FWIW, I think the truth lies somewhere in the middle. You do have to look at the real test data, you can't just rely on the Bin rating. There is a lot of variation within a bin, and jhinton's point is very valid about a low score in any one emission causing a vehicle to be down rated.

On the other hand, I also do not adhere to the idea of adding up all of a cars emissions and using that as a "cleanness" score either. A lot of folks over at tdiclub like to employ this metric, as it often favors diesels. Particularly as they often throw CO2 in there, which is basically the same as ignoring all other emissions. The toxicity, or environmental impact of every emissions compound is very different, often varying by orders of magnitude. As a facetious example, 32 pounds of cauliflower will kill you due to its sulfur content. Stricnine is fatal at 60mg (0.000132 pounds). So which would you rather sit down and eat a pound of?

Now the trick is, how do you determine what is most important? This is the subject of a lot of debate. Personally I tend to believe there are a lot of smart scientists who spend their whole lives studying this issue working for the EPA. I would tend to trust their determinations about the relative weighting of these compounds, as laid out in the bin criteria. I would think that by using a set weighting criteria one could arrive at a reasonable composite emissions score for any vehicle. I'm sure there are many out there who would disagree, as they feel the EPA and CARB are a bunch of looneys. I would agree that the judgment of these scientists can be tainted by politics.

For example, the 2007 EPA Tier 2 Bin 3 standards are:
CO: 2.1 g/mile
NMOG: 0.055g/mile
NOx: 0.03 g/mile

So by the EPAs determination, it appears that NMOGs and NOx are much more potent (by weight) than CO. From these numbers we could work up a weighting formula to compute an "air quality score".

(CO + (2.1/0.055)*NMOG + (2.1/0.03)*NOx) / 6.3 = (CO + 38.2*NMOG + 70*NOx) / 6.3

A score of 1.0 would indicate a vehicle that exactly meets the T2B3 standard, or a weighted equivalent. By this metric, here are some sample scores:

'08 Highlander Hyb:-- 0.0485
'07 Jetta 5cyl B2: -- 0.0851
'06 Honda Insight CVT:0.135
Camry Hybrid: ------- 0.147
'08 Honda Acc 4cylB2: 0.151
'06 Ford Escape Hy:-- 0.152
'07 Lexus RX400h4W:-- 0.154
'08 Lexus GS450h: --- 0.161
'08 Honda Accord V6B2:0.161
'04-'09 Prius: ------ 0.182
'07 Civic Hybrid: --- 0.199
'07 Honda Civic B2:-- 0.203
'07 Ford Escape Hyb:- 0.274
'06 Honda Insight MT: 0.305
'06 Honda Accord Hyb: 0.318
'08 Chevy Tahoe 5.3L: 0.668
'08 Toyota Camry 4cyl:0.674
'09 VW Jetta TDI: --- 0.692
'08 Saturn Vue Hyb:-- 0.707
'07 Lincoln Navigator:0.750
'07 Hummer H3 5cyl: - 0.791
'07 Cadillac Escalade:0.860
'08 Malibu Hybrid: -- 0.875
'07 Saturn Vue Hyb:-- 1.20
'07 Hummer H2: ------ 1.84
'08 Mercedes E320 BT: 2.78
'06 Jetta TDI: ------ 3.57
'99 GMC Suburban: --- 5.44
'06 Jetta Wagon TDI:- 6.21
'85 Mercedes 300d: - 10.1 (no NMOGs, not measured in 1985)
'85 Mercedes 300d: - 11.4 (subs HCNM for NMOG)

Of course this formula ignores PM. Since concerns about PM are another topic of hot debate, I've done the calculations both with and without for comparison. The T2B3 limit for PM is 0.01g/mi. This would lead to a corrected formula of:

(CO + (2.1/0.055)*NMOG + (2.1/0.03)*NOx + (2.1/0.01)*PM) / 8.4 = (CO + 38.2*NMOG + 70*NOx + 210*PM) / 8.4

The new scores with PM for the cars above would be:
'08 Highlander Hyb:-- 0.0364
'07 Jetta 5cyl B2: -- 0.0638
'06 Honda Insight CVT:0.102
Camry Hybrid: ------- 0.111
'08 Honda Acc 4CylB2: 0.113
'06 Ford Escape Hy:-- 0.114
'07 Lexus RX400h4W:-- 0.115
'08 Lexus GS450h: --- 0.121
'08 Honda Accord V6B2:0.123
'04-'09 Prius: ------ 0.136
'07 Civic Hybrid: --- 0.149
'07 Honda Civic B2:-- 0.152
'07 Ford Escape Hyb:- 0.206
'06 Honda Insight MT: 0.223
'06 Honda Accord Hyb: 0.239
'08 Chevy Tahoe 5.3L: 0.502
'08 Toyota Camry 4cyl:0.505
'09 VW Jetta TDI: --- 0.519
'08 Saturn Vue Hyb:-- 0.530
'07 Lincoln Navigator:0.563
'07 Hummer H3 5cyl: - 0.594
'07 Cadillac Escalade:0.645
'08 Malibu Hybrid: -- 0.656
'08 Chevy Tahoe Hyb:- 0.826
'07 Saturn Vue Hyb:-- 0.901
'07 Hummer H2: ------ 1.38
'08 Mercedes E320 BT: 2.14
'06 Jetta TDI: ------ 3.82
'99 GMC Suburban: --- 4.09
'06 Jetta Wagon TDI:- 6.38
'85 Mercedes 300d: - 19.5 (no NMOGs, not measured in 1985)
'85 Mercedes 300d: - 21.1 (subs HCNM for NMOG)

Of course, even this is far from perfect. These are the main factors measured in federal emissions testing, but there are many more. Particularly in CA. And we are not considering CO2 at all, which is much trickier to factor in. Still, I would say that the numbers above could be considered in the context of their relative CO2 output from fueleconomy.gov to get a good idea of the big picture. IMHO, since the Prius does very well on emissions, and has lowest CO2, its the clear winner if these two factors are the primary considerations. Based on the numbers for the newer HiHy, HyCam, and Lexus hybrids I expect to see even better numbers out of the '10 Prius.

Rob

 

The importance of each pollutant depends on already existent local concentrations, and who you are. E.g., ozone depleting pollutants matter to Aussies more than folks living at the equator; asthmatics take particular offense at particulates; and farmers do not like acid rain.

It's actually a lot more complicated than I make out, but the general idea is right. Also, so far as I know, criteria have never been downgraded so while CO may have been a much more important problem 20 years ago than today, the levels do not reflect an improved environment of that chemical.

 

Thats certainly true. There are also big regional variations, ie smog is perceived to be a bigger issue in big cities, some cities smog makeup is VOC limited meaning excess NOx can reduce actual smog production, other cities are not so excess NOx contributes to smog production. You also have the tradeoff of local impact vs. remote impact. For example, rural Maine has fairly poor air quality and acid rain issues due in large part to industrial emissions from Michigan and the midwest blowing across the great lakes. Maine has no jurisdiction to regulate emissions in other states, and the locals in those states have less interest in reducing emissions because they don't perceive a local benefit.

Rob

 

You make some good points Rob. However, as others have said, local issues and politics determine what types of pollution are considered important in different areas. You point out that CARB and the EPA weigh NOx, NMOG, and Particulates to be very important to reduce and tend to ignore CO. I agree since the EPA hasn't change the CO limited for passenger cars since 1994 though the have been continuously reducing allowed levels of the other regulated emissions.

However, the very smart scientists that set emission standards for the EU have a very different approach. First, they have split the regulations for diesel and gasoline vehicles.

------------------ CO ------ HC ------ NOx ----- PM
Euro 4 Diesel ---- 0.81 ---- 0.081 ---- 0.405 ---- 0.04
Euro 4 Gas ------ 1.62 ---- 0.162 ---- 0.130 ---- N/A
(Converted to g/mile)

In the EU, diesels are allowed more NOx and PM while gasoline vehicles are allowed more CO and HC.

Second, if you compare the EPA to EU regulations you will see that the Europeans allow much higher levels of NOx and PM even for the gasoline vehicles but much lower levels of CO

------------------ CO ------ HC ------ NOx ----- PM
EPA T2 Bin5: ---- 4.20 -----0.090 ---- 0.070 ---- 0.01
Euro 4 Gas ------ 1.62 ---- 0.162 ---- 0.130 ---- N/A
---------------- (-61%) -- (+80%) -- (+86%) --- N/A

Which group of smart scientists are right? Or is it as I suspect that it is more politics than science?

It gets even more interesting when look at the Euro 5 regulations that go into effect in 2009.


------------------ CO ------ HC ------ NOx ----- PM
Euro 5 Diesel ---- 0.81 ---- 0.081 ---- 0.292 ---- 0.008
Euro 5 Gas ------ 1.62 ---- 0.162 ---- 0.098 ---- 0.008

Notice that the Europeans are going to begin testing gasoline engines for PM. Why, because now that diesels have particulate filters, gasoline engines are putting out more PM than diesels. Some here on PriusChat want to believe that gasoline engines don't emit PM but a simple swipe of your finger on the instead of your exhaust pipe will show the truth.

What does this all lead to? Should be believe the Europeans that put more weight on CO2 and CO or the Americans that concentrate on NOx and PM? Me, I'll continue to look at them all as "important pollutants" and weigh them equally. I also think that we are at the point of diminishing returns with automotive emissions and our scientists and regulatory folks should start concentrating their efforts on Commercial vehicles. (Trucks, buses, trains, ships, off-highway) These vehicles still have emissions measured in whole grams while we are arguing about 10ths and 100ths of a gram in cars.

 

So now European's scientists are "very smart" when they produce guidelines which are more favourable for diesel, which again, produces a desired outcome for you?

Until you give some actual reasoning as to why the emissions from diesel or gas should be any different, I'm going to have to call BS and say it was done for political reasons. Meaning that the manufacturers would have a hard time producing diesels with the same NOx levels as gas cars which would make them cost prohibitive, so they lobbied the politicians to make it so. Scientists don't make policy, politicians do.

So again, you go back to weighing pollutants evenly because it's convenient for you, even though the effects of pollutants are not the same, pound per pound.

It's quite clear from the Euro 5 regulations that PM is far more important than the other pollutants. PM emissions must be a tiny fraction of CO, HC and NOx emissions. But not just for the Euro 5 regs, that's the direction all new regs are going. The other pollutant that is being pushed down? NOx. So it seems quite clear that PM and NOx emissions are very important, and perhaps even more important than CO and HC emissions which have not changed in the latest Euro 5 regs.

We are not arguing about 10ths of grams of differences, we are arguing about percentages. Just like the case where the diesel is "only" ~4c / mi more expensive (or ~50-60% more expensive), the diesel "only" is allowed to emit .2-.3 g/mi more NOx. Which happens to be 200-300% more which all of a sudden means something completely different when we are talking about driving vehicles billions of miles a year.

 

I agree. All has to be taken with a grain of salt. However, I'm not sure its 100% politics. In general US cities have seen much worse air quality problems than European cities. A lot of this simply has to do with differences in weather, geography, air currents, urban density, etc.

I'm not sure the differences are as different as you imply though. Its interesting to me that from Euro4->Euro5 they also left CO the same, and are only tightening regulation on NOx, and PM. It seems to me they are also indicating that CO is less of an issue. Its also important to note that you are comparing what has been Euro's cleanest standard (IV) to what is becoming the US's dirtiest (T2B5). I think a fairer comparison would also include T2B2 and SULEVII, and would include both diesel and gas.

Gas:
------------------ CO ------ HC ------ NOx ----- PM
Euro 4 Gas ------ 1.62 ---- 0.162 ---- 0.130 ---- N/A
Euro 5 Gas ------ 1.62 ---- 0.162 ---- 0.098 ---- 0.008
EPA T2 Bin5: ---- 4.20 ---- 0.090 ---- 0.070 ---- 0.01
EPA T2 Bin2: ---- 2.10 ---- 0.010 ---- 0.020 ---- 0.01
SULEVII: -------- 1.00 ---- 0.010 ---- 0.020 ---- 0.01

Diesel:
------------------ CO ------ HC ------ NOx ----- PM
Euro 4 Diesel --- 0.81 ---- 0.081 ---- 0.405 ---- 0.04
Euro 5 Diesel --- 0.81 ---- 0.081 ---- 0.292 ---- 0.008
EPA T2 Bin5: ---- 4.20 ---- 0.090 ---- 0.070 ---- 0.01
EPA T2 Bin2: ---- 2.10 ---- 0.010 ---- 0.020 ---- 0.01
SULEVII: -------- 1.00 ---- 0.010 ---- 0.020 ---- 0.01

Average: (assumes 50% diesel, 50% gas ldv fleet)
------------------ CO ------ HC ------ NOx ----- PM
Euro 4 Av ------- 1.22 ---- 0.122 ---- 0.268 ---- 0.02
Euro 5 Av ------- 1.22 ---- 0.122 ---- 0.195 ---- 0.008
EPA T2 Bin5: ---- 4.20 ---- 0.090 ---- 0.070 ---- 0.01
EPA T2 Bin2: ---- 2.10 ---- 0.010 ---- 0.020 ---- 0.01
SULEVII: -------- 1.00 ---- 0.010 ---- 0.020 ---- 0.01

If we take the Euro 5 Av numbers, and generate a new weighting formula from that, here are the new results:

(CO + (1.22/0.122)*NMOG + (1.22/.195)*NOx + (1.22/0.008)*PM) / 4.88 = (CO + 10*NMOG + 6.25*NOx + 152.5*PM) / 4.88

In this case as expected NMOG, NOx, and PM are somewhat de-emphasized compared to previous. A score of 1.0 equals the Euro5 gas/diesel average limit or its weighted equivalent:

'08 Highlander Hyb:-- 0.0164
'06 Honda Insight CVT:0.0210
Camry Hybrid: ------- 0.0251
'07 Lexus RX400h4W:-- 0.0272
'08 Lexus GS450h: --- 0.0313
'08 Honda Acc 4cylB2: 0.0415
'06 Ford Escape Hy:-- 0.0420
'08 Honda Accord V6B2:0.0456
'04-'09 Prius: ------ 0.0517
'07 Ford Escape Hyb:- 0.0584
'07 Jetta 5cyl B2: -- 0.0908
'07 Civic Hybrid: --- 0.103
'06 Honda Accord Hyb: 0.103
'07 Honda Civic B2:-- 0.119
'09 VW Jetta TDI: --- 0.171
'08 Toyota Camry 4cyl:0.174
'06 Honda Insight MT: 0.209
'08 Malibu Hybrid: -- 0.263
'08 Chevy Tahoe 5.3L: 0.313
'07 Hummer H3 5cyl: - 0.329
'07 Lincoln Navigator:0.346
'08 Saturn Vue Hyb:-- 0.431
'07 Cadillac Escalade:0.513
'07 Saturn Vue Hyb:-- 0.670
'07 Hummer H2: ------ 0.758
'08 Mercedes E320 BT: 1.03
'06 Jetta TDI: ------ 1.88
'99 GMC Suburban: --- 1.26
'06 Jetta Wagon TDI:- 2.91
'85 Mercedes 300d: - 17.7 (subs HCNM for NMOG)

Interestingly, the ordering doesn't change a whole lot. I think it does illustrate that in general the US standards are generally stricter. A car that was emitting ~11% of the T2B3 standard is only emitting about 2.5% of the Euro5(Camry Hybrid). In general things didn't change that much, as most modern cars don't put out that much CO, with some SUVs being the notable exception.

Here's a subset, with the Prius normalized to 1.0 so basically this is how many time dirtier than a Prius a car is using both weightings. I've also added the simple sum, normalized in the same way.

Car ------------ T2B3 ----- Euro5 ----- Sum
'06 Insight CVT- 0.75 ------ 0.41 ----- 0.12
'07 Camry Hyb -- 0.81 ------ 0.49 ----- 0.13
'08 Accord V6B2- 0.90 ------ 0.88 ----- 0.97
'04 Prius ------ 1.0 ------- 1.0 ------ 1.0
'08 Camry 4cyl-- 3.7 ------- 3.4 ------ 3.1
'09 VW JettaTDI- 3.8 ------- 3.3 ------ 3.9
'07 Cad Escalade 4.7 ------- 9.9 ------ 15.7
'08 Malibu Hyb-- 4.8 ------- 5.1 ------ 5.8
'08 Mercd E320BT 15.7 ------ 19.9 ----- 26.3
'06 VW JettaTDI- 28.1 ------ 36.4 ----- 3.5
'06 Jetta WagTDI 46.8 ------ 56.2 ----- 6.2
'85 Mercedes300d 154 ------- 342 ------ 24.5

I think this table illustrates several things. First, how the "summing up" emissions method used to be used to benefit old diesels. IE the old 300d goes from being 150-350 times dirtier, to only 24 times dirtier. It also shows that the new diesels don't really benefit from this or the Euro accounting, because they put out as much or more CO as modern gas engines. The E320 BT actually gets worse, due to its very high CO output, and the new Jetta TDI stays about even across all three. Lastly, it shows the effect of high CO output from SUVs like the Escalade as a larger penalty on the Euro and summing test. Another way of saying that would be that large SUVs are being tuned to take advantage of the US standard, or worse still the US standard has been tailored to make sure the big 3s large SUVs meet the standard ok.

I still think that strategy is the wrong answer. If you look at the US and Euro they are different, but they agree more than they disagree. Both say NOx, PM and HC/NMOG is much worse than CO, they just disagree by how much. I think you can make a good case for either the Euro standard or the US standard, or an average of the two, but I still think summing or equal weighting gives the wrong idea.

I do not believe this is true. While the amount of vehicle emissions seems small, the sheer number of vehicles on the road makes their contribution significant. Here are some numbers based on the data here:
BTS | Table 1-32: U.S. Vehicle-Miles

US Vehicle Miles Traveled (2005)
Passenger Car: 1,689,965,000,000 (1.69T)
Truck/Van/SUV: 1,059,590,000,000 (1.06T)
Tractor Trailer: 143,662,000,000 (143B )
2Axle 6+Wheel: 79,174,000,000 (79B )
Motorcycle: 10,770,000,000 (10.7B )
Bus: 6,646,000,000 (6.6B )
BTS | Table 1-32: U.S. Vehicle-Miles

US Fuel Consumption by Mode (2005)
Passenger Car+MC: 74,085,000,000 (74.1B gallons)
Truck/Van/SUV: 65,419,000,000 (65.4B gallons)
Tractor Trailers: 24,411,000,000 (24.4B gallons)
Air: 15,009,000,000 (15B gallons)
Rail Freight: 4,098,000,000 (4.1B gallons)
2Axle 6+Wheel: 9,042,000,000 (9.0B gallons)
Bus: 1,329,000,000 (1.33B gallons)
Transit: 788,000,000 (788M gallons)
BTS | Table 4-5: Fuel Consumption by Mode of Transportation in Physical Units

So light duty vehicles account for 92.3% of all vehicle miles driven in the US (2.76T out of 2.99T), and about 72% of all transportation related fuel use (139.5B out of 194.1B ). With that large percentage of the mileage and fuel use being racked up by the LDV fleet, they have to be much cleaner just to come out even to other sources. Also bear in mind that while they look like big numbers, the hdv and off-road emissions are measure in different units, usually g/kWh or something. That would be how many grams a 746HP engine would emit in an hour, and will be much larger than the g/mile used on vehicles. I do agree that we need much stricter regulations on MDV, HDV, rail, air, and non-mobile source emissions. They have gotten away with murder through loop holes designed to "protect business". I just don't think we are near the point where automotive emissions are no longer a substantial part of the whole.

Rob

 

Good, maybe I'll actually be able to get some work done today

Thanks for a good chat, have a safe trip.

Rob

 

Sadly, its Trillions in the US alone.

 

Look's like the Prius won. Fair and square.