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Score another one for the law of unintended consequences: In 2007, the Environmental Protection Agency (EPA) mandated stricter standards on new truck diesel engines in an effort to curb emissions of pollutants known as "particulate matter." But it was soon discovered that the only way to keep particulate matter from reaching the atmosphere was to trap the pollutants inside the engine and use the combustion generated by diesel fuel to incinerate the matter. Unfortunately, the process resulted in a drag on fuel economy, which, in turn, required an increase in the amount of diesel fuel used, which—in turn—effectively increased carbon emissions.

Glen P. Kedzie, vice president and associate environmental counsel for the American Trucking Associations, estimates that compliance with the 2007 standards has resulted in a 2- to 4-percent reduction in a truck's average fuel economy, while raising the cost of a new engine by $8,000 to $10,000 per unit.

This is not the first time that truck manufacturers, buyers, and leasing companies have taken it on the chin in the name of sustainability. According to trucking industry estimates, EPA clean-air rules in 2002 drove up engine costs by $3,000 to $5,000 per unit, while reducing fuel economy by 6 to 8 percent, due mainly to the use of then-new Exhaust Gas Recirculation (EGR) technology designed to reduce levels of nitrous oxide. And even-tougher EPA emission rules that take effect in 2010 will lead to a re-pricing of new engines to the tune of $10,000 per unit, according to Kedzie.