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September 26, 2005

Bus-ted!

A while back, the Seattle P-I ran a story about how Seattle's new diesel-electric hybrid buses weren't as fuel-efficient as advertised.  Our response was basically a shrug.  The chief benefit of hybrid buses, we argued -- particularly through the downtown bus tunnel, where many of Seattle's hybrids are routed -- is that they reducing pollution, not that they burn less petroleum.

Dieselhybridbus Except now, a study from the University of Connecticut (via this post at Green Car Congress) found that GM's hybrid buses really may not actually reduce pollution coming from the buses' tailpipes.  In fact, driving identical routes, the standard diesel buses seemed to emit a bit less particulate matter (a particularly nasty problem for diesel engines) than the hybrid buses.

This, of course, comes as a surprise -- the air in Seattle's bus tunnel's has seemed surprisingly pleasant to me, even after the city switched from all-electric to hybrid buses through the tunnel.  So I'm not sure what to make of it.  But still, there's probably a lesson to be learned here:  you have to be really careful not to be sucked into the hype surrounding new technologies. Sometimes the benefits don't pan out until the technology is refined; and other times, the benefits may never materialize at all.

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Clark, am I missing your famously subtle sense of irony here? If the air in the tunnel has stayed realtively clean even though diesel-hybrids are running within, it's because the buses hardly use their engines while underground. I thought they relied entirely on battery power, but it appears they actually have a special low-fuel mode while in the tunnel. http://www.busride.com/2004/07/seattle_rides_the_magic_bus.asp

So these hybrids reap a modest operational benefit: they save the time otherwise required to connect to the overhead wires when a bus arrives at the tunnel, and to disconnect when it leaves.

Seattle transit managers can be accused of a lot of missteps, but operating diesel engines full-bore while chugging through a tunnel full of commuters may actually not be one of them.

Of course, that won't be an issue until the tunnel reopens in 2007.

Posted by: Seth Zuckerman | Sep 26, 2005 2:41:58 PM

I'm sure you're right, Seth. The buses seem to work great through the tunnel -- and I've been in the tunnel when the electrical system failed and the old buses were chugging through on the diesel engines. Not pleasant at all.

But that's precisely why the study's findings were such a shock -- I had assumed that the air pollution benefits carried over, at least to some extent, once the hybrid buses left the tunnel. But perhaps not...unless there's something else here that I don't understand.

Posted by: Clark Williams-Derry | Sep 26, 2005 4:50:18 PM

"But still, there's probably a lesson to be learned here: you have to be really careful not to be sucked into the hype surrounding new technologies. Sometimes the benefits don't pan out until the technology is refined; and other times, the benefits may never materialize at all."

So true.

Posted by: Joseph Willemssen | Sep 26, 2005 5:12:10 PM

"So these hybrids reap a modest operational benefit: they save the time otherwise required to connect to the overhead wires when a bus arrives at the tunnel, and to disconnect when it leaves."

They also reap a benefit in that metro could completely decommission the overhead wires and thus remove one headache (having to work around the wires) to the retrofitting project. Also, I suspect that the power supply that the light rail system uses may not be compatible with the trolley wires that Metro buses use.

Posted by: Roy Smith | Sep 26, 2005 11:39:41 PM

It's good not to get hooked on new technology for its own sake, but don't forget that you need to not get sucked into believing a thinly researched thesis.

The professor who conducted the study noted that the hybrid manufacturer (GM) may have tuned the bus engines for performance, not efficiency. It's been discussed here as well how different one must drive to take advantage of a hybrid engine design. So the bus drivers may be using the electric power for zippier acceleration with no appreciable difference in pollution or fuel consumption, which is a benefit that is harder to quantify.

Also, he noted that the study only dealt with parallel, not serial, drive engines.

Finally, let's not throw the hybrid baby out with GM bathwater-- maybe this shows more problems with the manufacturer than the technology.

Posted by: Jason | Sep 27, 2005 11:20:37 AM

The article that Seth linked to does say they changed engine manufacturers last minute. There certainly could have been design change issues there, not to mention that the original engine was likely chosen for a reason. I wonder what was meant by the Cummins engine being "not certified for transit use".

Posted by: Matt Gangemi | Sep 27, 2005 4:11:37 PM

This may be a dimmish question, but why doesn't the city buy its equipment partly by performance contract? E.g., pay so much for the buses themselves, so much for each improvement in (specified) emissions over (specified) acceptable minimum in (specified) conditions measured with (specified) techniques? Performance bonds. Let the manufacturer decide whether a better alloy is a better investment than driver training. Etc.

It could be used for new wizzy LEED buildings, too.

Now, one city might not be able to outsmart a big manufacturer - they sell more often than any one city buys - but it sounds like a great way for the Kyoto cities to form up and help each other.

Posted by: clew | Sep 27, 2005 11:15:36 PM