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December 13, 2004

Hybrid Disappointment?

A non-hybrid bus, Seattle

Today, the Seattle Post-Intelligencer breaks what it seems to think is an important story: the diesel-electric hybrid buses King County Metro operates are burning a lot more fuel than anticipated. In fact, their fuel economy is no better than that of the older buses they are replacing.

This news is a little disappointing but ultimately doesn't matter much. Here's why, in a series of points that begin with the vehicle and zoom out to the cityscape.

1. Metro's hybrid buses are performing well in other ways. In particular, they emit far fewer local air pollutants. In fact, a last-minute switch from Cummins to Caterpillar engines to get cleaner emissions probably explains the increased fuel use. Diesel buses contribute a far larger share of health-threatening local air pollutants (such as deadly fine particulates discussed in today's Sacramento Bee) than of local fuel use (and the directly proportional emissions of climate-changing greenhouses gas carbon dioxide). For buses, burning cleaner matters more than burning less.

2. The hybrid buses are not serving routes on which they would be expected to save much energy: hybrids' fuel economy is best in stop-and-go traffic but Metro is mostly running the hybrid buses on express routes through the downtown bus tunnel. Regular engines operate most efficiently when they're somewhere near highway--or, at least, arterial--speeds: in the transit world, that's an "express." Hybrid technology saves the most energy at slower and variable speeds, where it can compensate for the tremendous inefficiency of the regular engine. In the transit world, that's a "local." Ideally, Metro would put hybrids on local routes, to save more energy. But Metro is unlikely to do that. The hybrids were bought to run in the downtown bus tunnel, where low particulate emissions and noise are important. And the bus tunnel is designed to serve expresses, not locals. So the hybrids are destined to remain ill-adapted to their main duties, at least from a fuel-saving perspective. (On the other hand, they're perfectly adapted to keeping the air clean in the tunnel.)

3. The technical energy efficiency of a transit vehicle is a wee-small consideration compared with its systems efficiency--which depends on how many people are on board. The best-case scenario for hybrid buses was that they might go an extra mile per gallon: in very rough numbers, maybe 4.5 mpg instead of 3.5 mpg. But getting one additional pickup- or SUV-driver off the road and on the bus saves almost exactly the same amount of fuel. And, of course, the power of transit is not that it can get one driver off the road but that it can get 40 per bus. So the main thing to worry about isn't what's in the bus's engine compartment but who's in its passenger compartment. A full-but-inefficient (3.5-mpg) bus uses a tenth as much fuel to move its passengers as would their own (16-mpg) SUVs if they drove alone. Hybrids don't make any appreciable difference in attracting new riders.

4. The "dirty little secret" of public transit -- which transit advocates and environmentalists hate to admit in public -- is that average transit trips in the United States are not much more fuel efficient than average trips in private cars, measured in fuel use per person per mile. (You can see this in tables 2.11, 2.12 and the related figures in Oak Ridge National Laboratory's Transportation Energy Data Book. An interesting discussion of the same issue, from independent researcher David Lawyer is here. And here's a chart we developed that compares the related variable of per-person CO2 emissions of transit at different capacities with other options: our chart corrects some of the flaws in Oak Ridge's approach but still shows regular transit not doing as well as you might expect.)

The reason is that transit is poorly utilized in the United States. Outside of rush hour and outside of central cities, the buses mostly run near empty. A typical bus needs to have at least five and typically more like seven passengers on board to start saving fuel, compared with those passengers driving alone.

And the reason for empty buses is that transit service is distributed politically, not through a market. Suburban and even rural political leaders want their share of transit service. So they bargain for bus routes that are almost guaranteed to run below the break-even level for fuel savings. This decision may be thoroughly justified because transit is partly a social service, rather than a public utility. But transit's fuel efficiency would be larger if transit service were allocated strictly to conserve energy.

5. Let me add, quickly: for individuals confronting the choice of whether to drive or take transit, taking transit almost always saves fuel, because you can assume that transit will operate whether or not you're on it.

6. The key to getting seven-plus passengers per trip is density. Other things--transit prices and passes, speed and reliability, safety and comfort--matter, too. But density matters the most, by far. Bad transit in dense neighborhoods attracts more riders than good transit in sprawling neighborhoods. Where enough people live or work close to a stop, transit saves money, fuel, and emissions. (The great debate on transit, among leading experts, is not whether density leads to transit use but whether transit investment, especially light rail lines, leads to density. The debate last appeared on this blog here.)

To close the loop, then: hybrid buses help reduce air pollution but they will never play a starring role in fuel economy. The land-use decisions that shape our cities are what ultimately determine the energy efficiency of Cascadia's transit systems, and ultimately, of Cascadia.

Posted by Alan Durning | Permalink


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» Talking sense about hybrid buses from Evergreen Politics
Alan Durning's response. to today's Seattle PI article about the apparently-disappointing fuel economy numbers for Seattle's new hybird buses is thoughful and to-the-point. [Unlike the sensational of those natteringly negative nabobs over at the PI. --... [Read More]

Tracked on Dec 13, 2004 7:54:23 PM


I'm just curious, how much more money do the hybrids cost than non-hybrid buses?

The reason that I ask is that although there are plenty of progressive politicians in King County, the bottom line is the bottom line. I'm guessing that in addition to the environmental benefits, that hybrid buses were also advertised for their fuel savings over their lifespan.

Posted by: Dave | Dec 13, 2004 4:36:53 PM

The government will pay for so called 'clean' hybrids but not so called 'dirty' diesel. Therefore every system is stuck buying them.

Posted by: François | Dec 13, 2004 7:06:52 PM

Hybrid buses cost more than regular diesel buses, though I can't remember how much at the moment. (I'm away from my files.)

But the real comparison shouldn't be to regular buses.

The hybrids have to operate in the bus tunnel. When the tunnel was built, some advocates suggested installing top notch ventilation systems to allow regular buses to use the facility. But others prevailed.

So now, the buses in the tunnel simply must be very clean: either electric trolleys or very low emission vehicles such as hybrids or, I suppose, compressed natural gas vehicles.

Metro says that hybrids were a bargain compared to the dual-powered (electric trolley and diesel engine) BREDA buses (such as the one pictured in my post above).

Posted by: Alan Durning | Dec 13, 2004 10:08:21 PM

As I understand it, the real problem with fuel efficiency comparisons is the engine switch, because the buses we're comparing the hybrids to use the older, dirtier but more fuel efficient engine. To make a fair comparison you'd have to compare the hybrids to new non-hybrids using the cleaner Caterpillar engines.

Posted by: Eric L | Dec 13, 2004 11:51:33 PM

I wonder if anyone considered simply using biodiesel for the tunnel busses? With biodiesel's big reductions in particulates, unburnt hydrocarbons, CO, and sulfur pollution (at the expense of slightly higher NOX), it might have been all that was needed, at a much smaller incremental cost -- even using the old, efficient-but-polluting engines.

Pundits are fond of pointing out that we'd have to devote a couple entire midwestern states to oil crops to replace petroleum with biodiesel. But surely the current 3 billion gallon stream of waste vegetable oil could be put to use in targeted situations like the tunnel run without requiring a single plant be grown specifically for transportation use.

Posted by: Jan Steinman | Dec 17, 2004 7:18:38 PM

Jan raises an excellent question. I'm guessing that Metro looked at that option, but I do not know.

I seem to recall an announcement that Metro is now blending a little bit of biodiesel into their fuel for all diesel buses. Anyone know the truth?

I do know that the emissions benefits of biodiesel are not always a better choice than cleaner engine technology or cleaner conventional fuels. For example, one lifecycle cost analysis conducted for garbage trucks in a major Northwest city found that biodiesel didn't compete well--in clean-air benefits per dollar spent. Engine improvements and different conventional fuel blends were more cost effective.

Of course, biodiesel from the waste stream -- as opposed to from dedicated crops -- brings ancillary benefits for climate and waste reduction.

This is an interesting topic that I'd like to know more about.

Posted by: Alan Durning | Dec 18, 2004 11:57:20 AM

First of all, the hybrids will be partially running diesel in the tunnel, not pure electric. The battery capacity is insufficient to make the run in the uphill direction.

Secondly, the hybrid is not an optimum design. The diesel engine turns all the time, even when not adding diesel power. The reason for this is that the auxiliary components such as alternator and compressors are connected to the diesel engine. A better design would be to have these units run off a transmission power take off, so that they could be powered either by diesel engine or electric. The diesel could be idled or shut down, reducing wear and tear and drag on the propulsion, just like the Prius does. I don't believe there is even a compression release or valve control during the freewheel use of the diesel.

I agree that the PI article was sensationalist rather than objective. What would anyone expect?

Posted by: sparky | Dec 18, 2004 11:39:03 PM

I recently learned about biodiesel, when a biodiesel truck visited the University of Oregon, and I'm wondering which major Northwest city conducted the biodiesel test with the garbage trucks. Do you remember?

Posted by: Michelle Parker | Dec 20, 2004 5:44:30 PM

Unfortunately, I cannot say yet. A Cascadian friend shared the results with me in confidence. Before long, though, the information will be public.

Posted by: Alan Durning | Dec 21, 2004 8:57:09 AM

Metro uses some biodiesel in their fleet. Unfortunately, B100 freezes at a higher temperature than regular diesels, so we can't go that route. Seattle's maintenance yards would know the exact percentage.There is a Gillig or New Flyer test bus painted with sunflowers in Seattle, I believe it uses at least B20. Remember, biodiesel is still much more expensive.

Posted by: Ben Schiendelman | Dec 21, 2004 10:22:07 AM