The Certification Challenge
Emissions certification of trucks and buses presently involves
testing of the engine only.
The Engine Compliance Program at the Environmental Protection Agency's
(EPA) Office of Transportation and Air Quality is responsible for
certifying engines for heavy-duty applications. The California Air
Resources Board (CARB) Mobile Sources Control Division performs
a similar function for certification in the state of California.
Both EPA and CARB use the same test procedures for urban bus engine
certification. Engines are certified on the Federal Test Procedure
(FTP) transient cycle. Emissions are measured and reported in units
of grams of emissions per brake horsepower hour (g/bhp-hr) delivered
by the engine under specific load regimes. The emissions are not
allowed to exceed certain standards set by EPA and California. Engine
manufacturers are responsible for complying with exhaust emission
standards.
Industry and regulators have recognized for some time the unique
challenge posed by hybrids in the emissions certification process
compared to traditional transit buses. Current hybrid-electric transit
buses often use new or unconventional engine technology that is
smaller and different in design, control and operation from conventional
engines. Although several of the first-generation hybrid engines
in use today did not meet EPA urban bus standards on the FTP cycle,
many demonstrated superior emissions performance in chassis testing
of hybrid-electric buses. Chassis-based emissions testing in the
United States only occurs on light duty vehicles, except in California
where chassis-based certification of medium-duty vehicles is allowed.
NAVC Hybrid Transit Bus Certification Workgroup
In response to this challenge, the NAVC formed the Hybrid Transit
Bus Certification Workgroup to develop a comprehensive protocol
for the testing and certification of heavy-duty hybrid-electric
vehicles engines.The NAVC Workgroup is a collaborative effort, comprised
of transit operators, bus manufacturers, hybrid system developers,
engine manufacturers, environmental advocacy groups, industry associations.
Over the course of several Workgroup meetings, the general consensus
among participants was that short-term certification testing to
help early market penetration should remain engine based and the
responsibility of the engine manufacturers.
More on the Workgroup
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