Using Travel Diary Data to Estimate the Emissions Impacts of Transportation Strategies: The Puget Sound Telecommuting Demonstration Project.

Transportation control measures are often implemented for their environmental benefits, but there is a need to quantify what benefits actually occur. Telecommuting has the potential to reduce the number of daily trips and miles traveled with personal vehicles and, consequently, the overall emissions resulting from vehicle activity. This search studies the emissions impacts of telecommuting for the participants of the Puget Sound Telecommuting Demonstration Project (PSTDP). The California Air Resources Board's emissions models, EMFAC7F and BURDEN7F, are used to estimate the emissions on telecommuting days and non-telecommuting days, based on travel diaries completed by program participants. This study, among the first of its kind, represents the most sophisticated application of emissions models to travel diary data. Analysis of the travel diary data and the emissions model output supports the hypothesis that telecommuting has beneficial transportation and air quality impacts. The most important results are that telecommuting decreases the number of daily trips (by 30%), the vehicle-miles traveled (VMT) (by 63%), and the number of cold starts (by 44%), especially those taking place in early morning. These reductions are shown to have a large effect on daily emissions, with a 50% to 60% decrease in pollutants generated by a telecommuter's personal vehicle use on a telecommuting day. These net savings are almost entirely due to the elimination of commute trips, as non-commute trips increased by 0.33 trips per person-day (9% of the total trips), and the non-commute VMT increased by 2.2 miles. Overall reduc- tions in travel and emissions of this magnitude are observed because the telecommuters in this sample are long-distance commuters, with commutes twice as long as the regional average. However, even as telecommuting adoption moves into the mainstream, its net impacts are still expected to be beneficial- a reduction in VMT and in emissions. It is important to note that when the level of telecommuting is considered (that is, the percentage of work days that employees actually telecommute), the weekly savings are a much smaller proportion of total weekday travel. Also, these findings represent average per-capita reductions; the aggregate (or overall, regionwide) impacts are determined by scaling these reductions by the number of program participants. Thus, the aggregate effectiveness of telecommuting must take into account the number of people likely to participate as telecommuters and how often they telecommute, not just the per-capita, peroccasion impacts.