Many states and cities require evaluation of the potential transportation impacts of proposed development and other projects, through environmental impact analysis, congestion management rules, or adequate public facilities requirements. In California, the California Environmental Quality Act (CEQA) requires public agencies to evaluate potential transportation impacts. The City of San Francisco currently uses the Highway Capacity Manual's Level of Service (LOS) intersection delay measure to identify transportation impacts. The San Francisco County Transportation Authority is encouraging the City to replace LOS with a measure based on the number of automobile trips generated by a proposed project. An auto trips generated impact measure would create consistency between the City's implementation tools and its Transit First Policy, which recognizes that short term LOS impacts will occur as improvements to transit, bicycling, and walking are implemented. This paper describes the Authority's effort to define a transportation impact analysis measure based on the volume of auto trips generated by a project. Potential "thresholds of significance" - the points at which the volume of auto trips generated by a proposed project constitutes a significant negative environmental impact - are described. The thresholds under consideration are based on the effects of auto traffic on mobility, quality of travel service, safety, neighborhood conditions, and other factors. The near term objective of the effort is to forward a new measure and threshold for adoption by the City for environmental impacts analysis purposes. In the longer term, the measure could provide a basis for a transportation impact fee.
Abstract