Public transportation agencies are on the cutting edge of investment in and adoption of innovative clean technologies and fuels while moving away from diesel-fueled buses and other long-standing technologies. That was the finding of Transit on the Cutting Edge of Clean Technology, an APTA report issued in late 2012.
In fact, the report states that clean fuel technological advances in public transit vehicles are significantly ahead of those used in personal automobiles.
For instance, the percentage of buses powered by alternative fuels in the U.S. rose from 2 percent in 1992 to 36 percent in 2011; the percent of cars powered by alternative fuels was only 3.2 percent in 2011.
“With U.S. greenhouse gases from transportation sources of all modes representing 28 percent of total U.S. emissions, it is important public transportation lead the way with innovative investments,” said APTA President & CEO Michael Melaniphy. “But it is not just good for the environment. Public transit systems that operate more efficiently can reduce operating costs.”
The industry has accomplished these gains by employing key technologies such as electric vehicles, new advances in battery technologies, diesel-electric hybrids, regenerative braking and energy storage, and the use of alternative fuels such as biofuels, natural gas, and hydrogen fuel cells. A brief summary of the report’s findings follows.
Electric and Hybrid Vehicles
Public transit agencies long have been in the forefront of incorporating hybrid buses into their fleets, including both diesel-electric and gasoline-electric hybrids. (See related story.)
According to the Transit Cooperative Research Program, a research arm for public transit funded by FTA and administered in part by APTA and the Transportation Research Board (TRB), diesel-electric hybrid buses are between 14 percent and 48 percent more fuel-efficient than conventional diesel buses, plus they significantly reduce tailpipe emissions. APTA’s 2011 Public Transportation Vehicle Database reports that hybrids account for about 17 percent of the new buses on order by public transit agencies.
Some agencies use all-electric vehicles. All heavy rail and nearly all light rail, trolleybuses, and commuter rail self-propelled cars are powered by electricity, while only a small percentage of buses and commuter rail locomotives are all-electric vehicles. Public transit agencies have been at the forefront of adopting plug-in hybrid technology as well, although the use of plug-in hybrids is still far from widespread.
Regenerative Braking and Energy Storage
Rail operators have used propulsion motor regenerative breaking technologies for many decades to capture breaking energy of their vehicles. A significant challenge in doing so, however, is that there is a limit to the amount of energy than can be stored within the power distribution system, thereby causing a portion of such electrical energy to be wasted as heat.
Consequently, in recent years public transportation agencies have focused more attention on coupling regenerative braking technologies with added energy storage devices (batteries, electro-chemical capacitors, and flywheels, for example) so the regenerated energy can be stored, used, or sold back to the grid for future use. Energy storage devices can be located either on board the vehicle or alongside the tracks, each providing certain advantages.
APTA and the Electric Power Research Institute formed a consortium of public transit agencies, representatives of the electric power industry, Sandia National Laboratory, and other interested parties to help the industry assess the potential of wayside energy storage and the implications for the coming smart-grid revolution.
Through a TRB grant, APTA directed a study to understand the benefits and applicability of wayside energy storage systems. The published report identified four primary functions of wayside systems that when used together could save energy and reduce energy costs for rail transit agencies: capture of regenerative braking energy, reduction of peak power demands, improvement in propulsion power quality and reduction of voltage sag, and use of wayside energy storage systems as replacements for electric utility power substations, saving on the cost of such substations.
Work continues to evaluate demonstration programs at participating transit agencies while new initiatives are beginning to examine on-board energy storage charging technologies.
Many public transit agencies are in the process of transitioning from traditional diesel fuel to alternative fuels including biofuels, natural gas, and hydrogen fuel cells.
* Biofuels. As of 2011, biodiesel fueled about 8 percent of buses (up from about 6.5 percent a few years previously) and about 5.5 percent of demand-response vehicles. According to APTA’s database, biodiesel vehicles account for about 7 percent of new buses and more than 14 percent of new demand-response vehicles on order by public transit agencies.
* Natural gas. Use of natural gas (compressed natural gas or CNG, liquefied natural gas of LNG, or blends) in public transit bus fleets started gaining ground in the late 1990s, growing from 2.8 percent of buses in 1996 to 18.6 percent by 2011. More than 40 North American public transit agencies now use buses powered by CNG or a CNG blend. As of late 2012, at least seven agencies were using buses powered by LNG. CNG and CNG-blend buses account for about one-third of the new buses on order by transit agencies, according to APTA’s database.
* Hydrogen fuel cells. Several U.S. public transit agencies use buses or other vehicles powered by hydrogen fuel cells, most built within the past few years. For example, AC Transit in Oakland, CA, is integrating 12 hydrogen fuel cell buses into its 680-bus fleet and, in April 2012, unveiled a large-scale, publicly accessible hydrogen production and dispensing station.
A wide array of federal, state, and local policies, programs, and initiatives have facilitated these advances, ranging from the Clean Air Act Amendments of 1990 to the American Recovery and Reinvestment Act of 2009. MAP-21, the surface transportation authorization law that expires on Sept. 30, 2014, includes a “deployment” program focused on low- and zero-emission public transit vehicles, providing grants for purchasing such vehicles and rehabilitating existing facilities to accommodate them.
“These policies should be maintained and expanded to enable public transit agencies to continue their leadership in transforming their fleets to clean fuel technologies that lead the way for the rest of the nation,” Melaniphy said.
The full report is available online.
The report that is the basis for this article was compiled from several sources, including APTA’s Public Transportation Fact Books and Public Transportation Vehicle Databases, DOT and FTA reports, the Department of Energy and the Energy Information Administration, TCRP, TRB, transit agency reports, the National Renewable Energy Laboratory, the New York State Energy Research and Development Authority, and national newspapers and trade magazines, among others.