NRDC: No Breathing in the Aisles: Diesel Exhaust Inside School ...

Over 100 school
districts across the
country operate
approximately 1,400
CNG school buses in
their combined fleets.
we detail in Chapter 4, over 100 school districts across the country operate approximately
1,400 CNG school buses in their combined fleets.
Fleet operators must also consider the need for a natural gas refueling station. 79 According
to Southern California Gas Company, 80 large refueling stations for fleets of 10 or more buses
range in price from $100,000 to $300,000, depending on whether a slow-fill or a fast-fill
fueling station is required and the number of gallons of fuel which can be pumped per hour.
Fast-fill compressors cost substantially more than slow-fill compressors, but school districts
rarely require fast-fill capabilities because a typical school bus fleet does not operate many
hours and can easily rely on an overnight fueling strategy. For smaller CNG fleets (e.g., under
10 buses), modular refueling units are most cost-effective. One manufacturer, Fuel Maker,
has available two different models for smaller fleets. The initial cost to install these units
ranges from $6,000 to $8,000 per bus, and fleets have the ability to later expand to
accommodate additional buses at a cost of approximately $3,000 per bus. 81 Larger units are
available from Fuel Maker, which can accommodate up to 10 school buses, at a cost of under
$100,000. 82
Government funding sources to date have failed to provide the incentives necessary for
school bus fleets to make the capital investment required for the construction of a natural gas
fueling station. School bus fleets, however, are ideal candidates for fueling infrastructure
funding because they fuel in one central location.
Liquefied Natural Gas
Liquefied natural gas (LNG) as a fuel of choice is garnering appreciation for its speed of
fueling (30 to 60 gallons per minute), fuel storage capacity, lightweight properties, and longrange
capabilities. Unlike CNG, LNG is cryogenically stored at temperatures of –260 degrees
Fahrenheit under normal atmospheric conditions and, lacking a pipeline infrastructure, is
delivered to fleet facilities by truck. Liquefaction stations that liquefy pipelined natural gas
on-site are under development, but the technology faces some economic hurdles and the fuel
quality may not be suitable for heavy-duty application (e.g., school buses). 83 Nevertheless,
on-site liquefaction may mature as the demand for LNG increases for truck and bus fleets
throughout the nation. The advantage of LNG lies in its density, reducing the volume needed
for storage by 60 percent in comparison to CNG. Because LNG tanks have a tendency to vent
if a school bus remains out of use for an extended period of time, the best application for this
promising technology may be for school districts that operate year-round.
Propane
Liquefied petroleum gas (LPG) is comprised of a simple mixture of hydrocarbons, mainly
propane gas, and is produced as a by-product derived from the processing of natural gas and
crude oil, mostly in the U.S. According to the Alternative Fuels Data Center, LPG has been
used as a transportation fuel around the world for more than 60 years. Refueling time is
comparable to gasoline. Propane engines also tend to last two to three times longer than
diesel or gasoline engines, due to less carbon buildup. Propane, however, has not been shown
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