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Open Access Publications from the University of California

Assessment of Out-of-State Heavy-Duty Truck Activity Trends In California


The California Air Resources Board's emissions inventory estimates indicate that ambient air quality in several regions of California is substantially affected by the exhaust emissions of diesel trucks. There are insufficient data to accurately model the energy and emissions impacts of interstate-traveling trucks, many of which may be registered and/or fuel out-of-state. Emissions inventory estimates are based on adjustments to data on California-registered trucks. These estimates may not reflect the effect of non-California-registered trucks' attributes and operations. Further, the effects of out-of-state fueling by California-registered and non-California-registered interstate-traveling trucks are also not currently captured. In Summer 2006, an interview survey of 433 truck drivers was conducted to characterize the vehicle attributes and operations of interstate trucks that travel in California. We estimate that non-California-registered trucks account for more than one-quarter of the Class 8 heavy-duty truck mileage on California roads. Also more than one-quarter of all Class 8 heavy-duty truck mileage in California is fueled by out-of-state diesel. The effects of this are disproportionately concentrated in four air basins – the Mojave Desert, South Coast, the Sacramento Valley, and the San Joaquin Valley – with considerable ambient air quality issues.

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