Transit agencies across the country are transitioning to natural gas. Natural gas buses offer environmental and economic advantages over diesel and other alternative fueled buses. Natural gas transit buses have a track record of clean, reliable, and cost-effective service in major metro markets and dozens of small communities. Today, approximately 11,000 natural gas buses operate across the country, and about 35 percent of new transit buses on order are powered by natural gas.
Major manufacturers offer transit buses, including North American Bus Industries, Orion, New Flyer, and El Dorado National, that are designed to run on natural gas. These buses are typically powered by the Cummins Westport 8.9L ISL-G engine that provides torque and horsepower comparable to that of diesel engines. For smaller shuttles and other vehicles, fleets can look to other OEMs and about a dozen small volume manufacturers (SVM) that retrofit new or repower existing fleets to run on natural gas.
Natural gas buses have a significant life-cycle cost advantage over diesel powered and diesel-hybrid powered buses. The fuel savings of natural gas vehicles over diesel vehicles is well known. Perhaps less well- known, but equally compelling, is the economic case for choosing natural gas-powered buses instead of diesel-electric hybrid-drive buses. While hybrid-drive propulsion systems show promise in a number of medium and heavy-duty vehicle markets, it is becoming increasingly clear that the initial purchase price premium and the cost of battery replacement for this technology is not justified by the incremental improvement in fuel efficiency, especially as diesel fuel costs continue to escalate.
The key to a successful NGV project is a well-planned and well-run fueling infrastructure. Transit operators must decide whether existing or new fueling infrastructure will be used and, if a new station is needed, what kind of station it will be and what business model will be used. There is no “best” or “right” option as each fleet has its own specific decision criteria and circumstances that will determine what is most appropriate.
Small transit or para-transit operations with only a few vehicles may find it best to use an existing CNG or LNG fueling station in the area, if available. When evaluating this option, it is important to know whether or not the station has the capacity to handle the additional load. This option may also be appropriate for a short-term field test with one or two vehicles before proceeding with a larger vehicle purchase commitment and station development contract.
If use of existing fueling infrastructure is not practical, convenient, or economical, it may be better to build a new CNG, LNG, or LCNG station. If CNG vehicles are planned, most transit agencies choose to install compressors that take local natural gas distribution company gas from lower delivery pressures up to 4,500 to 5,000 psi, store it on-site, then transfer it during the vehicle fueling process to the onboard CNG cylinders at 3,600 psi. Another option for fleets that do not have gas available to their site, is use of an LCNG fueling station, which compresses LNG (available via delivery or onsite liquefaction), then “flashes” it through a high-pressure heat exchanger to gaseous state before dispensing to the onboard 3,600 psi CNG cylinders.
If LNG vehicles are to be used and an existing nearby LNG fueling facility is not already available to handle the additional load, then a regular supply of vehicle grade LNG must be located and on-site cryogenic storage and dispensing equipment will be installed. Most of today’s available vehicular LNG supply comes from a limited number of large-scale production plants. Their large volumes create economies of scale but, due to their remote locations and transportation costs, their economic feasibility is directly impacted by distance from the prospective customer. Additional vehicular grade LNG production facilities are in development and advances in small- to mid-scale liquefaction technologies now make it possible to produce cost-competitive LNG closer to the fleets they serve, typically at a higher production cost but with lower transportation costs.
The design, capacity, and cost of a CNG, LNG or LCNG fueling station will vary based on 1) number of vehicles to be fueled, total daily fuel requirements and maximum hourly flow rate; 2) whether time-fill, fast-fill or both capabilities are needed (most transit agencies other than the very smallest that may rely on cutaway shuttles capable of a complete time-fill overnight require fast-fill capability); and 3) the level of remote station equipment monitoring.
Natural gas vehicles have the added benefit of positive “public perception.” Riders appreciate reliable, low-cost service. Riders also appreciate the quieter operation of natural gas buses, which operate at levels about 90 percent lower than diesel engines. Most importantly, use of natural gas communicates environmental stewardship and the importance of reducing our country’s dependence on foreign oil.
There are a number of OEM options for school districts. For more information and a complete list of EPA and CARB certified vehicles and engines, visit the Vehicle Availability page.
The U.S. Department of Energy’s (DOE) Alternative Fuels Data Center (AFDC) provides an online tool that lists available alternative fuel vehicles from leading OEMs. To view a list of natural gas school buses currently available, visit the Alternative Fuel and Advanced Vehicle Search.