Trends: Natural Gas Buses

Higher and unstable fuel prices have increased the use of mass transit over the past year, including trolley and bus ridership. That trend is likely to continue, so it’s important that the larger vehicles used for mass transit offer improved fuel efficiency and emissions. It’s also important that they address petroleum displacement through the use of alternative fuels when possible.

Buses represent a high-profile example of how natural gas can be successfully applied to buses of all types – urban mass transit, school buses, and shuttle buses. Lower fuel costs compared to gasoline and diesel buses is part of the reason. However, their clean air benefits are also important. Natural gas is often chosen as the most efficient and affordable pathway for agencies and fleets to meet environmental mandates. Because buses are usually fueled at a central location, infrastructure requirements are not a big issue, though building refueling facilities do require a substantial initial investment.

Mass transit buses have operated on natural gas for years and in other countries for decades. According to NGVAmerica, some 125 transit agencies are now operating over 10,000 natural gas transit buses on American highways. This trend is expanding, with over 20 percent of all new bus orders offering natural gas propulsion.

An example is provided by Los Angeles Metro, which operates over 200 Metro Liners that run on compressed natural gas (CNG). These buses are important in helping decrease emissions in the Los Angeles basin, a region noted for its poor air quality. These futuristic styled, 60 foot articulated Rapid Transit buses demonstrate how advanced mass transit technology can be merged with a mature propulsion technology – internal combustion engines running on natural gas.

Hybrid electric buses are also proving to be another successful ‘green’ technology. Hybrid buses typically use diesel engines now. So why not combine hybrid bus technology and cleaner burning natural gas? That’s what the San Diego Metropolitan Transit System is currently doing with its prototype hybrid CNG bus. This offers advantages since using natural gas in a series hybrid configuration improves range and fuel economy by 10 to 20 percent using the same volume CNG fuel tanks.

School districts across the nation widely use natural gas school buses, primarily because of their clean exhaust that's devoid of the diesel particulates that can be harmful to children. Studies have found that 90 percent less soot is emitted by natural gas buses compared to new diesel counterparts. Though the investment in a natural gas school bus is substantially greater than that of a diesel bus, lower operating costs can help recoup the initial investment.

Natural gas is becoming the fuel of choice for fleets operating at and around many of the busiest airports around the country. Here, a public access central refueling facility can not only service airport, rental car, and hotel shuttle buses, they can refuel public transit buses as well.

Additionally, natural gas could be the bridge to a hydrogen economy. Vehicles fueled with a blend of CNG and hydrogen represent the initial step toward future hydrogen-based transportation. HCNG, a blend of 10 to 50 percent hydrogen with the balance CNG, provides a way to build early demand for a hydrogen infrastructure long before hydrogen fuel cell vehicles are ready and affordable. Several transit agencies, including SunLine Transit in Palm Springs, California and TransLink in Vancouver, British Columbia, have tested HCNG in regular passenger bus service.

Renewable biogas is yet another source of fuel for natural gas vehicles. Produced by the decomposition of organic matter, purified biogas is being explored by many companies and agencies as a way of providing a potential pathway for sustainable natural gas transportation. Buses that run on renewable biogas are popular in Europe, with Sweden leading the way with about 1,000 biogas-fueled buses on the road.