1 table omitted
Ground-level ozone, a colorless gas, is a major constituent of smog. Since the early 1980s, controlled studies have demonstrated that exposure to elevated levels of ozone reduces inspiratory capacity in humans.1 In addition, ecologic analyses have indicated that daily emergency department visits for asthma exacerbations are elevated following days of high ozone pollution.1-4 The Partnership for a Smog-Free Georgia (PSG) is a state-sponsored program to reduce the number of days that ground-level ozone exceeds the national ambient air quality standard (NAAQS) in metropolitan Atlanta by providing federal and state subsidized commuting alternatives for local business employees. This report summarizes commuter data from three PSG partners to estimate reductions in emissions and monthly vehicle miles traveled that were associated with enrollment in PSG.
NAAQS for ground-level ozone is 0.12 parts per million during a 1-hour period. From May 1 through September 30, 1999, ambient ozone levels in Atlanta exceeded this standard on 24 days, maintaining the 13-county metropolitan-Atlanta region as an area of "serious" nonattainment of NAAQS. In December 1997, the Georgia governor s office issued an executive order requiring all state agencies to reduce single-occupancy vehicle commutes by at least 20% on days when NAAQS is expected to be exceeded. PSG was instituted during the summer of 1997 to help achieve this goal. Results of a study of 3 PSG partners were calculated using vehicle-miles-traveled formulas and emissions factors provided by the US Environmental Protection Agency.5
On May 1, 1998, the Georgia Department of Transportation introduced a comprehensive smog-reduction program to its 1900 employees. Baseline rates of commuter behaviors were assessed in April 1998 by a departmentwide survey asking employees how they "usually" commuted to work during the preceding year. Commuting behaviors were then assessed as part of the daily log-in procedure at each employee's computer terminal. Before PSG program initiation on May 1, 91.4% of Georgia Department of Transportation employees reported that their "usual" method of commuting was in a single-occupancy vehicle. During this baseline period, employees commuted an estimated 1033 vehicle miles per month, volatile organic compound emissions were an estimated 393 pounds per 100 employees per month, and nitrogen oxide emissions were an estimated 351 pounds per 100 employees per month.5 During May-August 1999, the percentage of all daily commutes in a single-occupancy vehicle decreased to 73.6% (a relative decrease of 19%), and vehicle miles traveled and their associated emissions decreased 11%.
The Georgia Board of Workers Compensation, which has 117 employees, became a PSG partner in May 1998. The agency conducted a baseline survey of their employees "usual" commuting behaviors during March 1998. Beginning in May 1998, all employees completed a daily survey of commuting behavior. Most (62.1%) employees usually commuted using a single-occupancy vehicle before initiation of the PSG program. Before PSG implementation, Georgia Board of Workers Compensation employees commuted an estimated 799 miles per employee per month, emitted 303 pounds of volatile organic compounds per 100 employees per month and 272 pounds of nitrogen oxides per 100 employees per month. During May-July 1999, the percentage of all commutes in a single-occupancy vehicle was 44.9% (a relative decrease of 28%). In addition, PSG program implementation was associated with a monthly decrease of 145 vehicle miles traveled per employee per month and an estimated 18% decrease in emissions.
Georgia Power/Southern Company has been conducting a prospective monthly survey of employee commuter behaviors since April 1997. During the baseline period of March-April 1998, an average of 587 (20%) of 2885 employees participated in the alternative commuting program. Following the repetition of seasonal promotional activities in April 1999, the average increased to 41.5% during May-July 1999 (a relative increase of 52%), and emissions were reduced 12%. To rule out any influence of seasonality on observed findings, participation rates for March-April 1999 were compared with those from March-April 1998. The employee participation rate increased 32%.
J Pierce, MBA, Partnership for a Smog-Free Georgia. S Carter, MBA, Georgia Power Company, Atlanta. D Orlando, Air, Pesticides and Toxics Management Div, Environmental Protection Agency, Region 4 Office. P Hortman, MS, Georgia Dept of Transportation; T Risko, MBA, State Board of Workers Compensation; KE Powell, MD, Div of Public Health, Georgia Dept of Human Resources. Air Pollution and Respiratory Health Br, Div of Environmental Hazards and Health Effects, National Center for Environmental Health; and an EIS Officer, CDC.
The metropolitan-Atlanta area ranks first in the United States in annual vehicle miles traveled per household.6 Because 53% of all nitrogen oxide emissions comes from mobile sources of pollution,7 programs that successfully reduce vehicle miles traveled in Atlanta may substantially reduce ozone-producing emissions and ozone-related health effects. Data provided by the PSG partners in this report suggest that PSG program implementation occurred concurrently with an 18%-21% decrease in single-occupancy commute rates and an 11%-18% decrease in monthly commute miles traveled and associated emissions.
The lack of a standard evaluation method among the PSG partners was an important limitation to these analyses. Georgia Power/Southern Company conducted a prospective survey to establish a baseline of commuter behaviors, and the other PSG partners conducted a retrospective survey. In surveys, employees selected 1 commuting option that was their "usual" method of commute. In these cases, pre- and post-intervention rates are not directly comparable, since post-intervention data reflect the proportional contribution of alternative commuting days to all commute days. However, Georgia Power/Southern Company estimated vehicle-mile reductions for their employees that were similar to those estimated for the other PSG partners. Subsequent analyses of employee commuting behaviors will be facilitated by a standardized approach to evaluation and by standard metrics to calculate vehicle miles traveled by PSG partners.
These PSG partners may have achieved the 20% reduction in single-occupancy commute rates mandated by the Georgia governor's office; however, how similar success can be achieved in a larger percentage of Atlanta s workforce is unclear. PSG can be expanded to include a greater number of local businesses. However, half of all employees of the 3 PSG partners in this report are not participating in the alternative commuting programs, although the average distance from these PSG partners to the nearest mass transit station is less than 1 mile. Increases in alternative commute rates beyond those already achieved may be facilitated by programs that continue to make alternative commuting options viable and accessible to working populations.
Future interventions also need to target commuting behaviors other than those related to the daily commute to work. Atlanta residents drive approximately 100 million miles per day, but only 21% of all automobile trips occur between the home and the workplace.8 Industrial emissions and nonwork-related behaviors (eg, noncommute driving, lawn-care practices, and gasoline and chemical solvent use) also contribute substantially to ground-level ozone and related health effects. Research is needed to evaluate whether employer-based programs like PSG also can reduce noncommute emissions among employee participants, their families, and co-workers. The integration of questions that incorporate day-to-day commuter behavior into state-based tracking surveys, such as the Behavioral Risk Factor Surveillance System, might provide an opportunity for this type of population-based program evaluation.
Corporate Action to Reduce Air Pollution—Atlanta, Georgia, 1998-1999. JAMA. 2000;283(19):2519-2520. doi:10.1001/jama.283.19.2519-JWR0517-4-1