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July 17, 2014

Switching Fleet to CNG Was Carefully Weighed Decision for DART

by Gary Thomas - Also by this author

Switching our bus fleet to compressed natural gas from liquefied natural gas and diesel was a carefully weighed decision at DART (Dallas Area Rapid Transit). But in the end, it was a no-brainer: go with the fuel source that will promote clean air while saving taxpayers $120 million in fuel costs over the next 10 years.  

It wasn’t something we took lightly. As a taxpayer-supported agency, it’s contingent on us to examine every option we have, and to balance cost-effectiveness with other factors such as service quality and environmental impact.

To that end, we evaluated many technologies, including “clean diesel” (which didn’t offer significant greenhouse gas or fuel-cost reduction), and diesel/electric hybrid buses (which were expensive to purchase).  

In the end, we decided to migrate our bus fleet — some 650 buses — to clean-burning, compressed natural gas (CNG). Although CNG vehicles cost more than diesel vehicles, the fuel to run them saves $1.50 to $2 per gallon. This immediate cost reduction translates into major savings over the life of a vehicle.

But it isn’t just as simple as pulling up to a different pump and filling the tank. There are a lot of “moving parts” to be accounted for – not least of all, the complex procurement of hundreds of CNG-powered buses.

Additionally, we had to design and install a network of filling stations to keep those buses running. In this, we partnered with Clean Energy, which designs and builds CNG stations all over the country.


Now that the new buses have been on the streets awhile, we can see that the benefits extend beyond saving tax dollars and doing our part for clean air. Customers appreciate that the engines are quieter — and since the exhaust is cleaner, even nearby non-riders can be thankful for the reduction in fumes. Riders also have given us positive feedback about the new buses’ comfort. Meanwhile, DART’s bus drivers have told us they will never miss the days of going home smelling like diesel.  

But make no mistake, for transit authorities like ours moving to natural gas pays off in a big way. In fact, as a result of transitioning our bus fleet to CNG, DART will realize fuel savings of roughly $120 million over the course of the next 10 years. Clean Energy co-founder and long-time Dallas resident T. Boone Pickens says, “The public-private partnership of DART and Clean Energy is saving millions of dollars” for DART’s cities, and he’s right.

At DART, we’re used to getting attention for our light-rail system. But the bus system is the backbone of our transit network — we offer 120 bus routes, and serve roughly 250,000 riders on any given weekday. Improvements in bus service impact a greater number of people than any other mode. All told, DART transports the people of Dallas and surrounding cities more than 39 million miles a year — the equivalent of more than 80 round trips to the moon.

The DART story should ring familiar to those who, like me, have called the Dallas area home for many years. The DART Service Area of 13 cities has a way of rising to challenges, and of embracing big-picture solutions. The very existence of DART is one such example. And our agency isn’t just thinking about how to reduce costs, enhance the customer experience and improve the environment for this year or the next — we’re a forward-thinking agency determined to improve the quality of life in the Dallas area for generations to come. It’s a privilege to serve this great region — and no matter how far we’ve come, at DART we’re always just getting started. Kind of like the region we are proud to serve.  

Gary Thomas is the president and executive director of Dallas Area Rapid Transit (DART).

Gary Thomas

President/Executive Director, DART


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  • Steve Hansen[ July 21th, 2014 @ 8:30am ]

    This article reads like a natural gas lobbyist's talking points. 1) DART says CNG buses are better for the environment than diesel buses. I recommend they read the stories in the NY Times ("Study Finds Methane Leaks Negate Benefits of Natural Gas as a Fuel for Vehicles" 2/13/14) and USA Today ("Natural gas vehicles worse for climate than diesel ones?" 2/14/14) to see how natural gas is a very questionable replacement for diesel. 2) DART says they're going to save taxpayers money by buying CNG buses. I suggest they read the recent story from the Houston Chronicle ("Economics of natural gas don’t always add up for fleets" 6/12/14). As one fleet manager stated about their experience with natural gas: "We’re not saving any money. I’m glad to hear we’re not the only one struggling with fuel mileage.” 3) DART says CNG buses are cleaner than clean diesels. I recommend they read the analysis from the Clean Air Task that compared new CNG buses with new clean diesel buses. The analysis, entitled “Clean Diesel versus CNG Buses: Cost, Air Quality, & Climate Impacts” (2012) found: “Both new diesel and new CNG buses have significantly lower emissions of NOx, PM, and HC than the older diesel buses that they replace. According to EPA’s MOVES emissions model a 2012 model year diesel bus emits 94% less NOx per mile, 98% less PM, and 89% less HC than a model year 2000 (12-year old) diesel bus. A model year 2012 CNG bus emits 80% less NOx, 99% less PM, and 100% less HC than a model year 2000 diesel bus." I know natural gas (i.e. Boone Pickens) is a major economic issue in Texas with a good deal of political clout. But it's alarming that DART has seemingly based their decision on faulty information.

  • David E Bruderly PE[ July 30th, 2014 @ 1:32pm ]

    Steve Hanson’s comments read like an Oil Oligarch / OPEC lobbyist’s talking points. 1) Carbon Footprint: Upstream / midstream methane leakage is a red herring issue – most of these releases can and should be controlled using state-of-the-art technology. In any case, similar quantities of methane are also released when oil is produced. Methane slip in engines can be reduced with engines optimized to use methane, rather than diesel fuel. 2) Cost: Experience has shown that once skeptical mechanics and operators are trained, the O&M costs for CNG vehicles are similar to O&M costs for diesel. Furthermore CNG buses do NOT have to deal with particulate traps, diesel exhaust fluid and engine problems associated with carbon buildup. 3) Criteria Pollutants: CNG buses are much better for the environment for the simple reason that tailpipe emissions from CNG buses are lower than diesel without the use of particulate traps and SCR with diesel exhaust fluid AND use of CNG eliminates human exposure to toxics from products of incomplete combustion of diesel fuel as well as exposures from water / soil contamination from leaks and spills of fuel. CNG engines are also quieter. 4) Unlike diesel fuel, American men and women do NOT have to die defending the production and price of this motor fuel; the flow of natural gas will be controlled by thousands of landowners and farmers in Ohio and Pennsylvania and New York, NOT a handful of foreign producers. 5) CNG is NOT linked to the global price of oil; widespread availability of natural gas motor fuels (LNG or CNG) gives the American consumer the opportunity to BREAK the market power of Oil Oligarchs and OPEC. Most Americans would rather spend their money in ways that create jobs in America than in ways that undercut the security of this Nation. 6) Natural gas motor fuels opens commercial pathways to even cleaner gaseous motor fuels and more efficient technologies, specifically the hydrogen fuel cell electric drive train. Natural gas Today

  • Kenneth Dallmeyer[ August 6th, 2014 @ 11:58am ]

    Neither of the comments address the impact on CO2 emissions of clean diesel or CNG (or for that matter any other fuel/propulsion technology.)

  • Steve Hansen[ August 7th, 2014 @ 12:01pm ]

    Dave E Bruderly PE's comments read exactly like what you'd expect from the Pickens Plan volunteer he serves as - a rehash of the natural gas lobby's favorite (and often inaccurate) talking points.

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Author Bio

Gary Thomas

President/Executive Director, DART

Gary Thomas is the president/executive director of Dallas Area Rapid Transit, covering a 700-square-mile service area with bus, light rail, commuter rail and paratransit services.


Taylor York

Staff Analyst, Western Riverside Council of Governments

Taylor has worked with the Western Riverside County Clean Cities Coalition since 2011. He also provides staff support for solid waste, energy and transportation programs at the Western Riverside Council of Governments. He holds a B.S. in Urban and Regional Planning from Cal Poly Pomona.


Dave Walsh

Project Manager, Sellen Sustainability

Registered Architect and a Project Manager Walsh, works with agencies, design and construction teams to implement measurable sustainability in transit projects.


Jennifer Turchin

Project Manager, Sellen Sustainability

Turchin is a licensed architect with expertise in all phases of architectural services.


Pamela Burns

Communications Supervisor, North Central Texas Council of Governments

Communications Supervisor, North Central Texas Council of Governments


Matt Stephens-Rich

Clean Cities Ohio

A graduate student at the John Glenn School of Public Affairs at Ohio State University, Matt Stephens-Rich is interning at Clean Fuels Ohio as part of the Clean Cities Workforce Development Program.


Richard Battersby

Director, Fleet Services at UC Davis

Richard Battersby is the director, fleet services, at University of California, Davis. He also serves as coordinator of the East Bay Clean Cities Coalition.


Steve Linnell

Director, Transportation / Energy Planning, Greater Portland Council of Governments

Steve Linnell is Director of Transportation and Energy Planning at the Greater Portland Council of Governments and Coordinator of Maine Clean Communities.


Yliana Flores

Alamo Area Clean Cities Coordinator

Yliana Flores is the Alamo Area Clean Cities coordinator for the Alamo Area Council of Governments Natural Resources Department, where she has worked on transportation issues since 2010.


Colleen Crowninshield

Manager, Tucson Regional Clean Cities Coalition

Colleen Crowninshield has worked for the Pima Association of Governments since 1994, where she has served as coordinator for the Tucson Clean Cities Coalition since 2002.


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