Study: Electric cars not as green as you think

I cracked the transportation chapter, but it looked like a mix of correct and incorrect analysis to me.

Twice, he seems to forgets that the energy required to fuel a vehicle is not the same as the energy required to move it over the ground. So, he'd substitute bicycles for cars, with no mention of the fossil fuel required to produce the fuel for the bicycle. He cites the Tesla as being >4x as efficient as his baseline car. Which I am pretty sure means that he ignores the inefficiency of electrical production and transmission, though I did not take the time to follow that up. I've done the electric car calculation for my plug-in Prius. Electrical miles in that car reduce my C02 output by 30% relative to gas miles, at the Virginia power generation mix. Not by anything like 75%.

Then he cites good examples. The London Underground averages (my calculation from his numbers) 140 passenger-miles per gallon. Or roughly the same as a Prius with three passengers. So, yes, an urban electric rail transit system with a high load factor will be efficient. From statistics I can glean, the Washington Metro clocks in at around 110 MPG.

But exemplary systems are not the average. Amtrak comes in a 43 passenger-miles per gallon, for example. Substantially better than the average US car, but not better than a Prius.

I'm not even sure where this is heading. Back in this thread, somebody said that the Prius was useless as a means to reduce environmental impact, but that public transport made a real difference. I cited Oak Ridge National Laboratories showing that, in the US, the average public transport system did not perform as well as the average urban Prius trip (though it does perform better than the average US car trip). Somebody cited statistics with incredibly good performance data for public transport. I suspected (but could not show) that those statistics were for fully-loaded buses and trains.

I think I can settle up with the notion that an exemplary, well-loaded electric rail urban transit system is between 2 and 3 times as efficient as the average urban Prius trip. That notwithstanding, I think ORNL correctly characterized average performance of US public transport.

Let me put this in the perspective of the original post that I was responding to.

Take a person traveling 100 miles in the average US passenger vehicle (21 mpg x 1.3 persons per trip). If you switch from the average US car to a Prius, you save 2 gallons of gas. If you switch from the average US car to the DC Metro, you save 2.75 gallons of gas. (London, it would be 2.95.)

The only point that I really wanted to make, in all of this, is that getting the average American to substitute a Prius for his or her current vehicle does reduce environmental impact. If you could get him or her onto a system as efficient as the DC Metro, it would reduce it somewhat more. But only somewhat. The biggest savings come from stopping the most inefficient uses of fuel. The ultimate impact of any fuel-saving alternative depends on both physics and behavior. If some drivers will substitute a Prius for their current guzzler, but won't or can't take mass transit, then the availability of the Prius reduces environmental impact of transportation.

 

The statistics really are educational to me. Specifically, advocating better mass transit is actually a much smaller incremental improvement than I would have thought.

This is very important since a lot of city to city rail connections have been proposed for Florida. To make those worthwhile, a big increase should be needed in "passenger-miles-per-gallon". The numbers I see here call into question the stated payoff of such a huge expense.

 

If you pack the metro trains like you saw in the trains in Japan, the efficiency will be 4-5X of the Prius.

 

Actually, by the stats given, it becomes even more clear that mass transit is even more of a benifit IF the average rider was driving a typically average vehicle.
If they were all driving a Prius it wouldn't be such a good deal.
I also believe an advantage not taken into account is the fewer vehicles on the road, leading to a small amount of better fuel efficiency (during borderline peak traffic) for those vehicles.

 

I tried to find the relevant data from NY and Tokyo.

I could not find the underlying data, but NY MTA press releases state that single-occupancy vehicles "up to" (in some press releases, or no qualifier in other) five times the C02 per passenger mile. That would put NY City transit at "up to" 105 mpg on average (taking the average single-occupancy vehicle to be 21 mpg.)

Press Release


I could not find the relevant statistics for the Tokyo subway. It would not surprise me if it were substantially above average.

The public transportation industry association itself estimated total savings from US mass transit. The research looks good to me. It was done by a local DC company (SAIC) that I've dealt with in the past.

http://www.apta.com/research/info/online/documents/climate_change.pdf


The savings are there, but they are not large, on average, for the US -- including the savings from reduced congestion. Here's the relevant paragraph:

"In 2005, public transportation reduced CO2 emissions by 6.9 million metric tonnes. If current public transportation riders were to use personal vehicles instead of transit they would generate 16.2 million metric tonnes of CO2. Actual operation of public transit vehicles, however, resulted in only 12.3 million metric tonnes of these emissions. In addition, 340 million gallons of gasoline were saved through transit’s contribution to decreased congestion, which reduced CO2 emissions by another 3.0 million metric
tonnes. An additional 400,000 metric tonnes of greenhouse gases (GHG) were also avoided, including sulfur hexafluoride, hydrofluorocarbons (HFC), perfluorocarbons, and chlorofluorocarbons (CFC)."

So, that's what the industry says about itself. On average, the industry itself estimates that the use of public transport reduces C02 emissions by 43% relative to the average private car. About half that is from the efficiency of the public transport, about half that is from reduced road congestion.

Savings would be higher if public transport were loaded more fully. Savings would be lower if average private vehicle efficiency were greater. But that's the US average.

EDIT: I finally found data for Tokyo, or, at least, for Japan Railway East district. Assuming that all of their trains are electric, they average out to 480 passenger-miles per gallon. So the intuition about packed Tokyo subway cars would appear to be correct (if they use no fuel other than electricity). Data taken from:

http://www.jreast.co.jp/e/investor/ar/2005/pdf/ar2005_21.pdf

That's 125B passenger-KM for 6.1B kwh.

I'm never quite sure what to do with electric utility generating losses in all of this, but the carbon release data for electricity are stated per KWH delivered, so from my perspective this is the right way to view it . That is, tyical generation is 1.2 lbs C02/KWH, so where a sole-occupant Prius releases about 0.4 lbs C02/mile, the JR East district releases about 0.06 lbs C02/passenger mile. Little over 10-to-1 ratio of "gas mileage" as calculated, little under 10-to-1 ratio of C02 release.