Greater Greater Washington


Metro switching most buses to alternative fuel

Metro is upgrading its bus fleet to replace older diesel buses with new hybrid-electric buses. Almost two-thirds of buses use alternative fuel today. The difference in miles per gallon is not substantial, but alternative fuel buses have lower operating costs and lower emissions.

Photo by jsmjr on Flickr.

DC lags behind some other cities in alternative fuel use for buses. LA uses 100% alternative fuel buses and New York has more alternative fuel buses, but they comprise a smaller proportion of the total fleet. DC has more alternative fuel buses than San Francisco's MUNI, but MUNI also operates electric buses and DC does not.

Metro does not plan to switch to entirely alternative fuels, according to Brian Anderson, Metro's Social Media Manager. Metro will continue to operate clean diesel fuel buses, which Anderson said must meet stricter EPA emissions standards.

Hybrid buses average around 4 MPG, while diesel buses average 3.5 MPG and compressed natural gas (CNG) buses average 3 MPG. The Metrobus fleet includes 1,530 buses of 15 different models of varying capacity and fuel type. (See a slideshow of the different bus models below.)

The newest buses come in two different models, the 2009 New Flyer and the 2011 New Flyer Xcelsior. These buses have slightly less capacity than the diesel ones but there are 412 of these buses, comprising about one-fourth of the total fleet.

In addition to the hybrid electric buses, Metro operates 460 CNG buses. Because they require special fuel, they can only be stored at Metro's bus garages at Bladensburg and at Four Mile Run in Arlington. Some of the CNG bus models have luggage racks and service Metro's airport routes to Dulles and BWI.

Metro also operates three longer articulated bus models and one short model. Two of the articulated models are versions of the New Flyer hybrid bus and the third is an older diesel model. Articulated buses must use the Northern bus garage near the former Walter Reed site, the Montgomery bus garage in Rockville, or the Bladensburg garage in northeast DC to accommodate the extra length.

The articulated buses run on high capacity routes like the S1, 70 and X2. The short bus is an older diesel model and runs on lower ridership routes like the D2 and M4.

The oldest buses in Metro's fleet are 15 year-old diesel models. The average lifespan of these buses is 15 years, so many of the oldest ones are ready for replacement. This 15-year lifespan is longer than the Federal Transit Administration's 12-year minimum retirement age for heavy duty buses but the Metro board uses extended specifications (see bottom of page 25) to procure longer lasting buses.

Metro rehabilitates all buses around their mid-life point and performs about 100 bus rehabs per year. Rehabs don't extend the lifespan, but Anderson said mechanics examine almost every part of the bus to prevent breakdowns. This process costs about $110,000 per bus.

Metro has 104 of the 2011 New Flyer Xcelsior hybrid buses and has added about 102 New Flyer hybrid buses per year between 2008 and 2010. There are more than 300 of the oldest diesel models in the fleet but Anderson said Metro doesn't expect to replace all the diesel buses until 2017, which means some buses could be 20 years old at retirement.

Buses that old would be not that unusual. Metro still had 19-year old bus models in the fleet in June 2009, but those buses are no longer in service. As Metro continues to face budget constraints, it's not surprising that some buses will remain in service beyond their target life.

Here are photos of each of Metro's bus types. All photos from WMATA.

Slideshow image
Jamie Scott is a resident of Ward 3 in DC and a regular Metrobus commuter. He believes in good government, livable communities and quality public transit. Jamie holds a B.A. in Government from Georgetown University and is currently pursuing a Masters in Public Policy at Georgetown. 


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Thank you for this article!!!!

We need more bus attention!

anwyay, a couple points:

1. How do the diesel/hybrids work -- I somehow expect them to be quieter, but they don't seem so in practice.

2. Has the collapsing price of CNG changed WMATA's acquisition plans?

3. Difference between diesel and clean diesel?

I don't think there is anyway to make diesel clean. CNG has many many advnatages from a pollution viewpoint. From what I read before, there were complaints about the engines and working on them, but I suspect that was more abotu the CNG price spike a few years ago.

by charlie on Feb 28, 2012 10:36 am • linkreport

How does the total cost of theses buses compare over their lifetime compared to diesel buses? I assume that the hybrid buses are way more expensive for initial purchase (I could be wrong). Also how would the economic benefits of lower emissions be calculated?

by TGE.oA on Feb 28, 2012 10:50 am • linkreport

The newest hybrid-electric buses are supposed to only use fuel to charge the battery but the battery powers the bus. The bus manufacturer claims the MPG is close to 6, but there isn't enough data to confirm that. That said, I've noticed the newest ones are quieter - the high pitched whining is at least better than the grumble of the diesel engine.

WMATA's bus procurement report in 2010 (which I link to in the article at various points) says that they're moving away from CNG. I'm not sure how that's changed in the last two years.

As you point out, diesel isn't ever really "clean" but the clean-diesel buses are supposed to filter emissions more.

by Jamie Scott on Feb 28, 2012 10:51 am • linkreport

These buses are not "alternate fuel." They use the same exact fuel...they just do so more efficiently.

The difference between 3.5mpg and 4mpg is still 15%. That's nothing to sneeze at. Over the 12 year life of the bus, you save almost two years worth of fuel.

I wasn't aware that there were buses that used a true diesel-electric drivetrain; that technology hasn't even made it into consumer vehicles beyond the Chevy Volt (though the Volt focuses a lot more on its battery propulsion, which is currently impractical for a bus). I'd imagine that on a bus, the batteries would be used mostly to keep the lights/AC on while the bus is stopped.

Almost every diesel locomotive built in the last 70 years has used a similar configuration (sans batteries), and it's good to see that this good technology is finally making its way into buses. It makes a lot of sense from an engineering perspective.

That said, if the technology really is that far along, it does offer numerous other advantages, and I can imagine that it would reduce the vehicle's operating costs and lifespan by a very large margin. As with traditional hybrids, regenerative braking recharges the batteries, and significantly reduces wear on brake pads/rotors. However, unlike traditional hybrids, a true hybrid also requires no transmission, and needs no mechanical coupling between the engine and the wheels. This cuts a lot of weight and wearable/unreliable components, and makes it possible to put the diesel generator anywhere on the bus.

by andrew on Feb 28, 2012 11:20 am • linkreport

Any filtering of emissions is welcome to me, as a bike commuter who finds myself stuck behind Metrobuses on a fairly frequent basis.

by Jacques on Feb 28, 2012 11:20 am • linkreport

How can you compare gallons of diesel to gallons of CNG? Do they have the same amount of energy in them? Do they cost the same?

Also, it sounds obvious, but Metro will need to put CNG fueling facilities in more of its bus garages if it wants to put more CNG buses on the road.

by Tim on Feb 28, 2012 11:26 am • linkreport

Also how would the economic benefits of lower emissions be calculated?

The economic benefits of clean air (lower health care costs, fewer work days missed due to sickness, increased life span) have generally exceeded their costs by a wide margin. There are numerous studies that quantify the costs and benefits of various clean air rules, although I'm not aware of any that specifically address the cost/benefit of cleaner buses.

As for DC, the city needs to do more to clean up the air. Dirty air in the summer tends to trigger my asthma when biking behind cars in the city (not so bad in bike lanes or cycletracks) and I imagine I'm not the only one. We need fewer code red (outdoor activity should be limited) and code purple (any time spent outdoors should be limited) air quality days.

by Falls Church on Feb 28, 2012 11:27 am • linkreport

"As you point out, diesel isn't ever really "clean""

Americans really are stuck in the 80's.

by Miguel on Feb 28, 2012 11:30 am • linkreport


It's always morning in America, and Reagan just took the solar panels off the White House roof.

by oboe on Feb 28, 2012 11:36 am • linkreport

Not sure if anyone else read the NYT article by shale gas skeptics:

The gist of it is that the claim we often hear that "we have 100 years of natural gas" may be overblown. The most "bearish" skeptics say we might have as little as 20 years. Probably just long enough to build out our CNG distribution infrastructure before the wells go dry. Sigh.

Bikeshare's looking more and more attractive.

by oboe on Feb 28, 2012 11:43 am • linkreport


Someone in that article said it reminds them of the dot com boom. im not sure how literal they meant to be, but look at the dot com boom. Stocks collapsed, companies went under. But the usage and importance of the internet continued to grow, and today many of the most highly valued companies ARE dot coms.

Suppose shale gas is overblown. Suppose the price of nat gas doubles. I think that means CNG would still be competitive for transit buses, esp where the infrastructure is already in place.

whether we should build out alot more CNG infrastructure is another question.

by AWalkerInTheCity on Feb 28, 2012 11:53 am • linkreport

Former driver for the Seattle system here...

Diesel buses are now very clean. Whoever said diesel can't be made clean is stuck in about 1998. With the switch to ultra-low-sulfur diesel fuel, particulate trap technology took off. If a particulate-trap equipped bus is properly maintained, you can rub your finger on the inside of the exhaust pipe and you won't come up with any soot.

Natural gas is great for heating houses, but it makes a lousy fuel for buses, for two reasons.

First, it's got a low power density, so you have to store quite a lot of it on board to make it through a typical day of service. Thus the heavy tanks on top of the CNG buses. Even with those tanks, the CNG buses have to be scheduled on shorter runs because of their range. Unlike a diesel bus, a CNG bus can't leave the base at 4 a.m. and stay in continuous service until the end of the service day at midnight. This makes operations more complicated and drives up costs.

Second, the engine makers don't have the budget to make engines specifically optimized for natural gas, so the engines are converted diesel engines. They have a narrow power band and no low-end torque -- not good characteristics in stop-and-go service. By contrast, the diesel hybrid powertrain is perfectly optimized for the stop-and-go environment, and the buses perform much better without nearly as much strain.

My view is that Metro should buy only diesel hybrids from here on out, and should phase out its CNG infrastructure as the fleet gets replaced. The diesel hybrids are just vastly better for the job.

by dal20402 on Feb 28, 2012 12:15 pm • linkreport

I didn't realize how many different types of buses there are. I understand that there are a variety of routes and thus there is a need for a variety of buses, but 15 different types seems like a bit much. Would there be any benefit to having fewer types of buses with regards to spare parts and training people to repair them? Perhaps have one type of articulated bus, one type of short bus, and 2 types of medium-sized buses?

by Teyo on Feb 28, 2012 12:26 pm • linkreport

I'm not stuck in the 1980's; even with modern diesels you have particulates.

Euro 5 gasoline car for PM: .005
Euro 5 diesel for car: .005

Euro 5 for bus (diesel): .02
Euro 6 for bus (diesel): .01

There is a world of difference between .01 and .005

I've heard similar complaints about CNG engines, but it is really unclear to me where the WMATA buses stand on the parallel drive trains. What Jamie described (electrics on the wheel, diesel is a generator) should be very clean as you can run that engine at an optimal point. However, I am not really sure that is what we have....

Is shale gas overblown? Over my pay grade. I doubt it will be as great as people say. The pollution advantages of CNG are worth a lot. A lot. Go to Europe, feel the side of building -- and that is diesel soot. Granted, you have a majority of the cars using it as well, which we don't have here.

by charlie on Feb 28, 2012 12:27 pm • linkreport

Someone in that article said it reminds them of the dot com boom. im not sure how literal they meant to be, but look at the dot com boom. Stocks collapsed, companies went under. But the usage and importance of the internet continued to grow, and today many of the most highly valued companies ARE dot coms.

Sure, and arguably the greatest benefit of the "internet bubble" collapsing was the "Gold Rush" of laying physical infastructure (i.e. fiber, etc..) But elsewhere I've heard the current (possible) shale bubble compared to Enron, or to the housing bubble. And there really was no lasting value created there. Just financial destabilization and ruin.

If it's just speculation getting out ahead of beneficial infrastructure, that's one thing. But if it's mostly this kind of stuff it could get ugly:

...Many of the email correspondents wonder if the industry is purposefully – even illegally – lying about the value of the finds. [Chesapeake Energy CEO] Aubrey McClendon told investors in 2008 that producing gas was only half its business model. The other half was reselling leases to other gas companies...

Anyway, who knows. Perhaps the "bulls" are right, and everything will be fine.

by oboe on Feb 28, 2012 12:29 pm • linkreport

I was referring not to the financial consequences, but to the real market changes. Maybe banks some banks will collapse due to shale - but since thats a much smaller piece of bank portfolios than housing, thats unlikely to blow up into an economy challenging crisis, even discounting for financial sector reforms. My point is that if a fraction of the gas is there - say one quarter - that could still be fraud of huge proportions, bring down companies much like the enron thing, etc - but there will still be more natural gas in the USA than we though 10 years ago, and the equilibrium price will be lower than it was. Now I do NOT know what the price of NG has to be to justify NG export facilities, or widespread CNG dist facilities - or even getting back on topic, an additional WMATA CNG facility (which I would hope wouldnt take 20 years to build). I am pretty sure that it will make sense to keep adding CNG buses to the already CNG equipped facilities - I am especially thinking of the one in Arlington, since the services buses in northern virginia.

by AWalkerIntheCity on Feb 28, 2012 1:53 pm • linkreport

Charlie, current diesel hybrid powertrains are really somewhere in between serial and parallel, just like the Toyota hybrid drivetrain in cars. The diesel and electric motors are connected by a planetary gearset that allows the powertrain controller to vary their contributions as it sees fit. From a stop, the electric is doing almost all the work. As speeds go up, the diesel provides more, until at highway speeds the diesel is the main contributor. This saves a great deal of wear on the diesel (from full-throttle starts) and some fuel.

by dal20402 on Feb 28, 2012 2:05 pm • linkreport

Count me as a CNG skeptic. I've never driven a CNG bus, but I have driven CNG cars. Very short range, no trunk space (to account for a larger fuel tank).

Plus, the explosion in natural gas resources is the result of techniques like hydrofracking, which has some serious economic consequences - groundwater contamination, the required use of a great deal of fresh water to get the gas out, and requires the emission of a great deal of greenhouse gases just to get the gas out as well. In short, it's not as clean as we'd like it to be.

by Alex B. on Feb 28, 2012 2:20 pm • linkreport

@Jamie -

Actually the difference between 3.5 and 4 mpg is huge huge huge.

MPG is the wrong unit. You don't go out and buy $10 worth of fuel and then figure out where you can go. You go places and have to pay the cost for that distance. So, the useful unit is gallons per 100 miles, or similar. (In europe the rating is liters per 100 km, and in fact fleet averages under US CAFE standards are effectively calculated with gallons per mile).

3.5 mpg > 28.6 gallons / 100 mile
4 mpg > 25 gallons / 100 mile

25 gallons is still huge, but Metro has saved 3.6 gallons per 100 miles.

3.6 gallons is a lot. Think about how much a car's milage would have to improve to save that much fuel.

Say you get 20 mpg for your sedan. Thats 5 gallons / 100 mi. You'd have to raise your milage to 71 mpg to save as much gas as you save moving a bus from 3.5 to 4.0 mpg.

If you have a car that gets 30 miles per gallon, moving from 3.5 to 4.0 mpg has saved more fuel than your car uses so you would have to go past infinity to decrease your consumption as much...

Metro buses also log a lot of miles, so this technology is very very important for air pollution and climate footprint.

(This is one reason why much of the discussion amongst the hypermilers can be rather silly!)

by DavidDuck on Feb 28, 2012 8:14 pm • linkreport


Thanks for looking up the Euro standards...

But the fact is that the DPF diesels are orders of magnitude better than diesels from 10 years ago (some of which are still out there, of course). Now (under Euro 6) its a factor of 2.

Diesel particulate is deadly stuff, and DPFs have to be carefully maintained. (I do see newish buses that is very discouraging).

But likewise, CNG buses produce NOx, probably formaldehyde, other junk. They are not pristine, especially with the poor optimization that dal20402 notes and many of us have smelled. They have at best a marginal advantage over diesel for climate purposes, and if the fuel system has any level of leaks, they could be a lot worse for climate.

I'd rather see the bus agencies put their infrastructure investments into hybridization and efficiency than NG fueling.

by DavidDuck on Feb 28, 2012 8:21 pm • linkreport

"DC lags behind some other cities in alternative fuel use for buses. LA uses 100% alternative fuel buses and New York has more alternative fuel buses, but they comprise a smaller proportion of the total fleet. DC has more alternative fuel buses than San Francisco's MUNI, but MUNI also operates electric buses and DC does not."

So really DC only lags behind LA.

Maybe one day ggw contributors will stop glorifying San Francisco and NYC as perfect, urban utopias, and realize that DC trumps them and their transit systems in many ways. Both DC's Metrobus and Baltimore's MTA bus systems are nation leading when it comes to adoption of alternative fuel technologies, but from the tone of the excerpt you would think that DC's backwards compared to most cities.

by King Terrapin on Feb 29, 2012 3:30 am • linkreport

A couple of pieces of information to add to a nice article on the WMATA bus fleet.

Hybrid-electrics have a diesel engine that runs a motor which produces electricity to run the bus. Because the motor runs at a generally constant speed it is more efficient than standard diesel engine propulsion. (Same deal for hybrid-electric cars with gasoline motors.)

Clean diesel vs. "plain" diesel -- simply the difference in new engines and tailpipe emission standards between older diesel motors and newer ones. EPA standards for public transit buses have, until recently, been much stricter than for diesel trucks. Now the standards are similar if not the same.

The bus manufacturers generally claim that the emission profiles across fuels are now basically equal due to improvements in diesel engines and tailpipe filters. Retrofitting existing garages to safely store CNG-fueled buses is quite expensive. Building a new garage that accomodates CNG-fueled buses from the start is cost competitive with a garage for diesel-fueled buses or a mixed fleet.

Metrobus riders would greatly benefit from new garages that could accomodate more articulated buses. WMATA could offer more capacity on routes more efficiently with more articulated buses.

by Steve Strauss on Feb 29, 2012 9:05 am • linkreport

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