Transportation 23: 163-190, 1996. © 1996 Kluwer Academic Publishers. Printed in the Netherlands. Forecasting telecommuting An exploration of methodologies and research needs SUSAN L. HANDY l & PATRICIA L. MOKHTARIAN 2 1 Community and Regional Planning Program, School of Architecture, The University of Texas at Austin, Austin, TX 78712-1160, USA; Z Department of Civil Engineering and Institute of Transportation Studies, The University of California at Davis, Davis, CA 95616-5294, USA Accepted 21 June 1995 Key words: forecasting methodologies, technological substitution, telecommuting, trans- portation modeling Abstract. Transportation planners increasingly recognize telecommuting as an important trend. But while they often advocate te!ecommuting as a transportation demand management strategy, transportation planners have made little progress toward incorporating telecommuting into transportation forecasts, at least partly because of the limited data available. In this paper we explore four alternative methodologies for forecasting telecommuting and discuss the kinds of data that must be collected before these methodologies can be applied. The first approach is trend extrapolation, using curves of technological substitution. Sufficient data are currently available to produce forecasts, albeit highly uncertain forecasts, using this approach. However, even with better data this approach does not address underlying factors and trends that will affect the future of telecommuting. As a result, we explore three additional approaches that should produce more reliable forecasts but which require new data and knowledge about telecommuting: analyzing the characteristics of telecommuters in contrast to nontelecommuters, analyzing factors affecting the individual choice to telecommute, and incorporating telecommuting into tradi- tional transportation forecasting models. Introduction As congestion and air quality problems in metropolitan areas worsen and calls for doing something about these problems increase, transportation planners in the US are tuming to telecommuting as a potential strategy for managing travel demand. The Clean Air Act Amendments of 1990, for example, require states to include Employer-Based Trip Reduction Programs in their State Implementation Plans; include among the transportation control measures that employers can use to achieve their vehicle occupancy goals is telecommuting. ISTEA, the Intermodal Surface Transportation Efficiency Act, provides enough flexibility in funding categories that federal funds can be used to establish telecommuting programs. The federal government as