United States
Environmental Protection
Transportation and Air Quality
Transportation and Regional
Programs Division
March 2002
With 4,400 propane-
powered vehicles in its on-
road fleet, the Texas
Department ofTransporta-
tion (TxDOT) is a leader
in the use of alternative fuel
Driven in part by a Texas
law mandating that all state
agencies purchase alternative
fuel vehicles, the department
has been using propane-
powered vehicles since 1992.
Today, these vehicles, along
with 1,000 vehicles pow-
ered by natural gas, com-
prise more than half of the
departments total on-road
fleet. Propane vehicles are
also popular in Texas
because propane is less
expensive than gasoline and
is manufactured in the state.
For more information,
contact Don Lewis ofTexas
TxDOT at (512) 416-
Clean Alternative
One in a series of fact sheets
More than 60 million Americans use propane gas for every-
thing from heating and cooling their homes and businesses to
powering their barbecue grills. Propane is also used to fuel
more than 350,000 vehicles on our roads today, from taxicabs and school
buses to police cars. In fact, with more than 5,000 fueling stations nation-
wide, propane is the most widely used alternative fuel to date.
Propane (otherwise known as Liquefied
Petroleum Gas or LPG) is a byproduct of
natural gas processing and petroleum
refining. In its natural state, propane is a
colorless, nontoxic gas—at least 90 per-
cent propane, 2.5 percent butane and
higher hydrocarbons, and the balance
ethane and propylene. An odorant is
added to the gas so it can be detected for
safety reasons. Under moderate pressure,
propane gas turns into a liquid mixture,
making it easier to transport and store in
vehicle fuel tanks. Compared with gaso-
line, propane can lower carbon dioxide,
carbon monoxide, and other toxic
dual fuel (i.e., propane and gasoline) for
between $1,000 and $2,000. Conversion
typically includes adding a special fuel
tank to the vehicle's trunk, which can take
Propane has been used as a transportation
fuel since the 1940s. Today, auto manu-
facturers offer a variety of light- and medi-
um-duty propane-powered vehicles,
primarily used by vehicle fleets. Many of
these vehicles have two separate fuel sys-
tems, allowing the vehicles to run on
either propane or gasoline. Other automo-
biles can be converted from gasoline to
Actual emissions will vary with
engine design; these numbers
reflect the potential reductions offered
by propane, relative to conventional
•	Potentially lower toxic, carbon
dioxide (CC^). carbon monoxide
(CO), and nonmethane hydrocar-
bon (NMHC) emissions.
•	Rich calibration shows high NMHC
and CO emissions, but lower nitro-
gen oxide (NOx) emissions.
•	Lean calibration shows slightly
higher NOx emissions, but lower
CO and NHMC emissions.
•	Estimates based on propane's inherently
"cleaner" chemical properties with an engine
that takes full advantage of these fuel proper-

up a space about the size of a spare
tire or larger. Also, in converted vehi-
cles, the propane fuel system increas-
es the weight of the vehicle by
approximately 100 pounds.
Propane refueling stations are
located in all 50 states, typically at
service stations, propane dealerships,
and equipment and truck rental facil-
ities. Many fleet owners have also
installed refueling facilities on site.
Propane storage tanks can often be
bought or leased through existing
propane providers. An online data-
base maintained by the U.S. Depart-
ment of Energy contains the
locations of refueling sites through-
out the country. For the vehicle
owner, refueling time for an LPG
vehicle container is similar to filling a
gasoline or diesel tank.
Propane and gasoline are comparable
in price per gallon. Propane costs
tend to fluctuate with oil prices and
can spike during periods of increased
demand, such as harsh winters. Vehi-
cle owners can avoid these price
swings through long-term service
contracts and bulk-fuel deliveries.
The energy content of propane is
less than gasoline, meaning it
achieves fewer miles per gallon than
gasoline. As a result, more propane
(and a slightly larger fuel tank) is
needed if the vehicle is to travel the
same distance as a similar gasoline or
diesel vehicle. In addition, propane
vehicles are more expensive than
their gasoline-powered counterparts,
roughly $3,000 to $4,000 more for
light-duty vehicles and $4,000 to
$5,000 more for medium-duty deliv-
ery trucks. These costs are expected
to decrease as more propane vehicles
are manufactured and sold.
Those who drive propane-powered
vehicles assert that there are no sig-
nificant driving differences between
dedicated propane vehicles and gaso-
line-powered vehicles. In fact,
propane vehicles have a higher octane
rating than gasoline, allowing for a
higher compression ratio in the
engine and greater engine efficiency.
This also reduces engine "knock" and
allows the engine to run more
smoothly. Because the fuel is already
in a gaseous state, it mixes readily
with air in the combustion chamber
to allow for nearly complete combus-
tion. This reduces certain exhaust
emissions, such as carbon monoxide,
and minimizes problems with start-
ing the vehicles in cold weather.
Propane in its liquid state has the
lowest flammability range of any
alternative fuel, which reduces the
chances of a vehicle fire. Because it
becomes a gas when leaked, however,
it is more likely to ignite than gaso-
line and other liquid fuels; propane
gas when leaked can fill a room and
form a flammable layer against the
ground or floor. Nevertheless, in case
of a spill outdoors, propane is non-
toxic, slightly soluble and biode-
grades rapidly in soil, water or air. If
stored in an enclosed space, proper
ventilation and leak detection sensors
are needed to increase safety, since
the gas can displace the air necessary
for breathing.
There are no special maintenance
requirements for propane vehicles,
other than having the vehicle ser-
viced by a professional familiar with
the fuel storage and delivery system.
For More Information
EPA's Alternative Fuels Web Site otaq/consumer/
National Propane Gas
1600 Eisenhower Lane
Suite 100
Lisle, IL 60532-2167
Phone: 630 515-0600
Fax: 630 515-8774
Web site:
Propane Vehicle Council
1155 Connecticut Avenue, NW.
Washington, DC 20036
Phone: 202 371-6262
Fax: 202 721-4204
Web site:
Alternative Fuel Refueling
Station Locator
Web site:
Alternative Fuels Data Center
Web site:
National Alternative Fuels Hotline
Phone: 800 423-1 DOE
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