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Like the boy who cried wolf too many times, California Air Resources Board has the challenge of proving that it can create an air-quality regulation based on sound science before it starts limiting diesel emissions on used construction machines.

This week's story by Robert Carlsen explains why CARB won't be enforcing its current slate of off-road fleet rules because the underlying emissions data were based on—in CARB's own words—a "guesstimate." Lately at CARB, it's been one research scandal after another. This loss of trust will be tough for CARB to regain.

The construction industry can claim victory this time, but it is not out of the woods yet. It is up to CARB to prove that a public health risk still exists, and it must build its regulatory case with valid logic and data to back up those assumptions. And it plans to do just that in revising its off-road fleet rules.

I predict that we'll eventually see CARB enforcing fleet rules of some kind, though they won't be as stringent as what was originally proposed. My cover story in 2006 showed why this "in-use" regulation was created and how it impacted construction fleets around the country.

It is interesting to note that contractors generally support limiting emissions of older off-road machines—especially through voluntary financing mechanisms such as tax incentives and grants, rather than regulation.

Why? Not only does the public have to breathe the black smoke billowing out of the tailpipe, but so do construction workers.

Maintenance costs also plummet when older machines are overhauled with cleaner-running engines. So one can easily build a business case to retrofit, repower or replace rather than do nothing.

That said, CARB now needs to clean up its act before it demands the same from California's contractors.

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