Tuesday, May 22, 2007

Transit Energy Efficiency: A Myth?

One of the principles of faith held by supporters of public transit is that public transit is more energy efficient than the private auto. I certainly thought that to be the case. The RTA's Moving Beyond Congestion Final Report states that public transit is about "twice as efficient as private vehicles" in terms of energy use (pg. 11 of 140).

The most recent edition of the National Traffic Statistics casts some doubt on this article of faith. Table 4-20 has comparative data on British Thermal Unit (Btu) per passenger mile. It shows that over time bus transit's comparative advantage in energy efficiency over the passenger car and even the aircraft has shrunk almost to zero. Here's a summary of the data:

BTUs Per Passenger Mile

Aircraft (Domestic Flights)
1980 5,742
1990 4,932
2000 3,883
2003 3,463

Passenger Car
1980 4,348
1990 4,269
2000 3,589
2003 3,570

Transit Bus
1980 2,742
1990 3,723
2000 4,147
2003 3,496

The data appear to be a bit wiggly, as many of the recent figures are "revised." Nonetheless, it shows that on a per passenger mile basis in 1980 aircraft travel consumed 2.1 times and passenger car travel consumed 1.6 times the energy as travel by transit bus. By the year 2000 travel by bus transit consumed more energy on a passenger mile basis than both travel by aircraft (1.1x) and passenger car (1.2x). Since 2000 it appears that transit's energy efficiency has improved on a passenger mile basis. It is a bit better than the private car but still less efficient than domestic air travel.

What accounts for the long-term deterioration in bus transit's energy efficiency on a passenger mile basis? First, the fuel economy gains for bus transit appear to have been less (plus/minus 16.7 percent--data is inconsistent) over the past 25 years than the fuel economy gains for the private car (43.1 percent).

Second, passenger loads have dropped significantly. In 1980 the passenger load was 17.4. In 2004 that figure dropped to 11.0. (I derived passenger load by dividing total passenger miles into total vehicle miles.)

In other words, it appears over the past 25 years public transit agencies have rolled out significantly more service relative to demand and used vehicles that have become less fuel efficient on a comparative basis with the private car. Has the long association of energy efficiency with transit become a shibboleth or have I mangled the data unforgivably?


Anonymous said...

Love them British Thermal Units (BTU's) almost as sexy as Bond Refinancing Premiums (BRP's) which generate a lot more interest in this region. Sadly, the only real transit use for BTUs here is that it serves as a real good measure of total Press Releases expressed as an annualized unit of degree heat transfered to the Illinois Legislature. Get it?

jackonthebus said...

In addition to passenger demand being down (resulting in relatively empty buses in outlying areas, unless replaced with 30 footers), the average transit bus has worse fuel mileage and fewer seats than, say 30 years ago. A GM 40 foot new look bus had 53 seats; you are lucky if a 40 foot low floor has 40. Some transit agencies reported that fuel economy went down when the new looks were replaced. Also, the fact that CTA exercised the rest of its options for the New Flyers without giving the hybrids the one year test promised (have the series hybrids even been received?) might indicate that it does not take that method of saving fuel seriously. At least it indicates that CTA hasn't yet found the fuel savings sufficient to overcome the $200,000 excess cost of each hybrid bus.

Moderator said...

Anonymous--Got it. Does the equation end with PU?

Jackonthebus--What significance, if any, is the fact that the private transportation sectors (aircraft and private car) improved their energy efficiency much more than the public sector transit bus?

Anonymous said...

I'm glad you're getting it because for a long time I thought only I was getting it but it turns out that regional interests have been "giving it" to everybody uniformly-- sort of like Social Justice with a major gene mutation. In that sense we've all been "getting it" and are likely to continue to "get it" whether we "want it" or not. Are you still "getting it"? But maybe like me you're one of those people who "just don't get it" in which case you should continue to "avoid it" How 'bout now? Still "getting it"?

Justin said...

I think you're right, no mangling (um, not sure I "get it" though). If loads fall from 17 to 11 people, buses would need 50% more fuel-efficient engines just to keep up, on a BTU/pax-mi basis.

A couple of words of caution on the data though, which might help explain the wiggliness:

1) The BTS table includes all auto travel, including interstates in Montana and the like where cars are pretty efficient, and where buses would be too. Cars might compare less favorably in an urban operating environment.

2) Despite the footnote, the BTS table must rely on an average vehicle occupancy number to estimate auto passenger-miles. They appear to pull this from Highway Statistics, which uses NHTS for AVO. The results are sensitive to this.

3) Does the BTS table include SUVs and light trucks, or cars only?

4) I agree that buses, at current loads, may not be much more energy efficient than autos. But don’t forget rail, and if the buses feed rail…

5) My own two cents: energy consumption is not always the same as pollution produced, or petroleum consumed. For example, would hybrid buses' electric power from regenerative braking count as BTUs? If buses ran on solar panels, their BTU/pax-mi might still be higher, but I’d prefer them to cars! :)

jackonthebus said...

The transit authorities want more subsidy, because they aren't efficient, in this and other ways. I don't know if regenerative braking would save enough to overcome the capital cost of a hybrid bus, but NYC and Toronto are buying them, and CTA is not.

pc said...

Aha, but CTA did indeed just start running 20 hybrid New Flyer buses. CTA's passenger loads are also higher than the national average.

jackonthebus said...

PC: Testing 20 hybrid buses is comparatively nothing, when, while during the test, it orders 400 diesel ones. By contrast, according to Orion Bus, Toronto has ordered 510 hybrids, and by now, New York has over 450. You are easily impressed by CTA P.R. The 10 hybrids delivered to this point just gave Daley something to show the Olympic committee.

Anonymous said...

What was that line? 'Liars, damn liars, and statisticians.' Something like that...

Just a few points before we all abandon mass transit forever:

- Buses are not mass transit. They are a possible option but are not representative of mass transit in general. In fact, it isnt too hard to imagine them being the least efficient option. That said, the data by the BTS still shows buses to be the most efficient converter of BTU's into Passenger Miles (except motorcycles, God forbid the BTS or US-DOT acknowledge that people use non-motorized vehicles to get around!)

- The declining efficiency of buses compared to private transit and airplanes has a few main causes. The most important probably being the increase in traffic in exactly those areas where most buses are used. Since the motor companies destroyed the trolley system in America, cities have been planned around the personal automobile which stops infrequently (if ever) to load or unload passengers. Is it any wonder that bus-sized vehicles (eg buses) stopping frequently in ever congested areas with declining passenger loads will experience declining efficiency? A much better idea would be dedicated trolley/tram lanes and, in a perfect world, public ways planned around pedestrians, bikers, agile mass-transit, and the needs of commerce (delivery trucks etc). To abandon mass transit because buses have not experienced the same increasing rates of BTU/PM efficiency is akin to... Well its so absurd i can't even think of a proper metaphor.

- Because buses and cars utilize the same system of roads and, in general, the same power systems (ie, IC engines), are both subject to artificially low fuel prices, and, most importantly, share the same passenger pool, the idea that as ridership declines and congestion increases buses will experience a rate of efficiency increase lower than cars is a sort of 'no shit' conclusion. Justin's post makes this pretty clear.

- Moderator, are you serious? Buses are a poor transit solution, but for some it is the only option. Your post suggests that transit in general is inefficient, but you provide one study to back it up. Hopefully you are just playing devil's advocate so that we can shore up our defenses against anti-transit, anti-urban, uber-liberatarians like Wendell Cox. If not, I wish I could say I was more dissapointed, but a quick reading of your archives suggest that you have trouble with statistics and numbers. Why not stick to the policy/politics side and focus on Chicago, which you seem to be quite adept at. And on a linguistic note the meaning of 'begs the question' has absolutely no connection to 'raises the question'.

Anonymous said...

Anonymous May 26, 2007 3:40:00 PM CST:

Get your facts right. Buses do all the heavy lifting. Look at the ridership figures-- they kill the rail numbers. In addition, and this is not understood by many, buses also subsidize rail. Buses run on the same highways as cars and trucks so infrastructure costs are substantially lower than rail and the good routes turn a profit. However, you can't use them for massive bond sales, they don't demonstrably increase property values and they don't show very well when riding in to the loop from the north shore in a seersucker suit with a NYTs tucked under your arm. In short, snap out of it.

Anonymous said...

May 26, 2007 6:47:00 PM CST:

My last post (May 26, 2007 3:40:00 PM CST) may have been a bit too snarky, but my facts are correct and yours, simply, are not. While I find your reverse classism gross and strange, imagining myself in a seersucker suit brightened my day...

When you assert that "they [buses] kill the rail numbers", I assume you are referring to the national averages of buses share of transit: passenger miles-43.6%; or unlinked trips-59.9% compared to heavy rail (in which the el and similar systems belong) of 29.3%(PMs) or 28.7% (UTs). If you meant something else, please ignore the rest of this and let me know what you do, in fact, mean.
The trouble with looking at those figures (besides the fact 14% (PMs) and 31.2% (UTs) differences dont neccesarily constitute a numerical slaughter) is that they aren't very helpful when looking at major metropolitan transit systems and comparing rail and bus use because they include all those areas where no capital-intensive rail systems have been built. Looking at figures for Chicago, New York, Boston, and Philadelphia, buses clearly do not "kill" rail, and in many cases the opposite is the case, even more so if, like the BTS study, you are comparing PM figures. All of this data is available in the 2006 American PT Association Fact Book, which you can get on their website: www.apta.com.

"Buses subsidize rail" ? I would really like to see your numbers for this. Are you implying that farebox revenue from buses goes to supporting the less efficient, flashy and 'upper-class' (you brought class into it, not me) heavy rail? That makes no sense specifically because farebox revenues never cover operating or capital expenses (APTA). If you mean, instead that they feed rail, then you are right. But what does that prove, transit systems are just that, systems; they feed each other.

Lastly, Im afraid I missed your point (if there was one at all). Mine was simply that its foolish to try and start a discussion about transit efficiency (a very neccesary discussion indeed) with a single chart about national trends in a blog supposedly about the future of transit in NE Illinois. Further, because the Moderator opened the door with the post in which he (genuinely?) seemed to suggest that mass transit is doomed because it is inefficient (which the numbers do not indicate), I took it upon myself to point out how silly an idea this was. I simply meant to suggest that we need (in light of their decreasing rate of efficiency increase --what the BTS study actually showed) transit modes that exist independently from the system of city streets and traffic that is designed for personal automobiles rather than public buses, systems that can also be more amenable to carbon-neutral power sources (but of course, this is not neccesarily so).

"Snap out of it"... Err, what? Thanks for the advice, I have no idea what you mean by this, but until you (and the Moderator) decide to look past the numbers into what they actually mean, I'll offer you the same piece of advice.


pc said...

@Jack: Your quote was that "CTA is not" buying hybrids, which is wrong. You're right that they're not doing nearly enough (but also wrong about my being too easily impressed, as I'm as jaded as the best of them), but 20 is not 0.

Their excuse that they're "testing them in our extreme climate" is bunk, of course, since (a) hundreds are in service in Minnesota and our winter ain't got nothing on theirs and (b) even CTA's hybrids are even made in Winnipeg, aka "polar bear capital of the world." CTA faces unpredictable fuel prices, comparatively generous capital funding but stingy operating funding and increasing restrictions on diesel emissions, which all point to the need for hybrid drivetrains.

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