Truck rule based on flawed data, ARB staff admits
Published: April 21, 2010
By Daniel Weintraub
model that the Air Resources Board used to justify historic
restrictions on diesel emissions from off-road construction equipment
may have attributed twice as much pollution to those heavy trucks as
they actually produce, according to interviews with ARB staff.
coupled with the effects of the recession on the construction industry,
means that the excavators, backhoes and graders that operate in
California are producing only a fraction of the pollutants that the
board believed was the case when it adopted the regulations in 2007.
The industry has been pushing the air board to repeal or at least
suspend implementation of the rule, which requires contractors to get
rid of old, heavily polluting engines and retrofit others with filters
to capture the diesel particulate matter before it reaches the ambient
From the beginning, construction contractors have contended that the
rule was misguided, would force some contractors out of business and
had costs that exceeded its benefits.
Now the Associated General Contractors, a lobbying group that is
leading the fight against the regulation, has released a report
alleging that the ARB model exaggerated the emissions by a factor of
about four. Combined with the effects of the recession, the contractors
say, emissions today are only one-sixth as high as the board projected
they would be at the time the regulation was adopted.
The consequences could be huge for the industry – and for other
polluters. If the numbers used by the ARB were wrong, then the
construction industry might not have to do much more to meet the
emission standards the board adopted through 2025. But since the state
is still required by the federal government and its own rules to meet
overall goals for reducing pollution, other sources, perhaps on-road
trucks and buses, will have to make up the difference.
“What this reveals is that emissions from the off road equipment in the
construction industry are far below not only the board’s original
estimate, but far below most of its targets,” said Mike Kennedy,
general counsel for the contractors’ group. “Without any rule of any
kind, the construction industry will exceed the board’s objectives for
[Nitrogen oxide] emissions through 2025 and it will exceed the
objective for particulate matter emission up to the year 2020.”
The air board is meeting today to begin discussing how to proceed. The
board’s staff plans public workshops later this spring to discuss the
problem, and plans to make a recommendation to the board this summer. A
decision about the future of the off-road truck regulation will
probably come in September.
staff disputes the contractors’ figures and its conclusions about the
future of the rule. But they concede that the model was flawed and will
need to be rewritten.
that our previous estimates were a little high,” said Kim
Heroy-Rogalski, who manages implementation of the off-road truck rule.
“We do believe we need to take a look at it and adjust for whatever
inaccuracies might have been in there.”
Benjamin, chief of the board’s mobile source analysis branch, said an
internal review of the model has concluded that earlier estimates were
off by a factor of between 1.4 and 2. That means the board may have
attributed twice as much pollution to the construction trucks as they
In addition to the errors in the model, the board’s staff has
determined that off-road construction activity in 2009 was only about
half what it was in 2006, because of the recession. Correcting for both
the error and the effects of the recession could reduce estimates of
emissions to levels far below what the board originally required the
industry to meet.
The problems with the computer model came to light after a study by UC
Berkeley researchers compared the amount of fuel actually used by the
trucks to the amount that the ARB model projected they would use. While
Heroy-Rogalski and Benjamin said that study oversimplified the problem,
they acknowledge that it did prompt them to reexamine their model, a
review that uncovered serious flaws.
The model is based on assumptions about the number of construction
vehicles in use in California, their age, the size of their engines,
how often they operate and the intensity at which they run. This last
variable, known as the “load factor” may be responsible for much of the
error the board is addressing now.
Benjamin said the state uses a formula for the load factor patterned
after one used by the US Environmental Protection Agency. The EPA, he
said, is revising its model and California hopes to follow suit.
“The load factor is the most problematic,” Benjamin said. “We are
hoping we can incorporate the results of their testing programs. But it
is not a straightforward and simple process. It’s quite time consuming.”
Heroy-Rogalski said that, despite the problems with the model and the
hardships of the recession, the air board still has an obligation to
protect public health.
“You can go into this, watch different people debating technical
points, but it is important to step back,” she said. “The ARB
recognizes that these are really challenging rules to comply with. We
recognize there has been this huge recession. Yet the rules are still
important from a public health perspective. We’re trying to achieve a
balance, making sure we achieve our public health goals and still give
as much relief as we can.”