TPB News

Economic Downturn Slows Anticipated Growth in Driving Through 2020, but Pushes Up Forecasts of Vehicle-Related Emissions

Jul 2, 2012

Despite forecasts of slower-than-expected growth in population, employment, and driving in the Washington region through 2020 because of the economic downturn of the last few years, vehicle-related emissions of harmful pollutants could still be as much as 16% higher in 2020 than previously expected because economic conditions have also slowed the rate at which consumers are replacing older vehicles with newer models that have significantly lower emissions.

The detailed findings come as part of an annual analysis conducted by the Transportation Planning Board to estimate future emissions in the region based on forecasts of population and employment growth and existing plans in Maryland, Virginia, and the District of Columbia to expand the region's roadway network and transit system.

This year's analysis relied on the latest update to the region's long-range transportation plan and population and employment forecasts that were recently revised by the Metropolitan Washington Council of Governments to reflect the results of the 2010 Census and other trends caused by the economic slowdown. Recent traffic counts were also used to get a better idea of existing travel patterns in the wake of the slowdown.

Forecasts of the total number of households in the region by 2020 were revised downward by 0.5% -- or about 14,100 households -- while employment was revised downward by 0.4% -- approximately 17,400 jobs. Construction of new highway capacity was reduced by nearly 200 lane-miles, mostly just outside the region in Howard and Anne Arundel Counties. Together, these changes are expected to result in 0.8% fewer vehicle trips and 2.3% fewer vehicle miles of travel in the Washington region in 2020 compared to forecasts made during last year's analysis.

Under economic conditions like those prior to the national downturn, such decreases in driving overall would have been expected to result in emissions in 2020 being about 1% lower than previously forecast. But the results of a 2011 "vehicle census" by the TPB show that, since 2005, the average age of all the cars and trucks on the region's roads has increased by 1.21 years. Using this more recent snapshot of the region's vehicle fleet, which shows older vehicles with higher emissions staying on the road longer, the TPB's analysis found that emissions of harmful pollutants would be higher in 2020 than previously thought.

In the latest analysis, emissions of fine particle pollution (PM2.5) -- which causes respiratory ailments -- would go up 1.5%, emissions of smog-forming volatile organic compounds (VOCs) would go up 12.8%, and emissions of nitrogen oxides (NOx) -- another ingredient in the formation of smog -- would increase by 15.7%. The increases are so sizeable because newer vehicles in the last few years have been equipped with more sophisticated emissions controls that make them much cleaner to operate than the older vehicles they are replacing.

These results demonstrate the important effect that consumers' vehicle-purchasing behavior can have on air quality, and that the effects of vehicle-purchasing can significantly outweigh the effects of reduced driving. Although forecasts of higher-than-expected emissions in 2020 are not a major cause for concern with regard to public health, they do matter to those responsible for setting future emissions reductions targets for the region. Under federal regulations, the region must set and demonstrate progress toward achieving such targets in order to continue receiving federal funding for transportation.

The economic downturn of the last few years has resulted in forecasts of population, employment, and driving that are lower than previously thought. More important from the perspective of vehicle-related emissions, however, is the simultaneous slowdown in the rate at which individuals, families, and businesses are replacing older vehicles with newer models that have significantly lower emissions. By 2020, this trend could push emissions of some harmful vehicle-related pollutants up by nearly 16% compared to forecasts made just last year. Such information will be of use to those trying to determine how best to ensure that the region's air quality continues to improve over time.

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