Automobile traffic congestion, and our collective behavior as automobile drivers, is front and center in environmental conversations and debates. A primary reason being that traffic congestion can dramatically affect air quality, emitting pollutants including nitrogen oxide, sulfur dioxide, carbon dioxide and ozone. These pollutants can have severe impacts on public health, especially in urban areas, and contribute to global climate change. In addition to air quality impacts, traffic congestion causes economic impacts including delay, an inability to accurately predict travel times, increased fuel consumption, and potential safety hazards.

When evaluating traffic impacts of both existing and proposed projects, state and local agencies have traditionally used the level-of-service (LOS) measure to categorize traffic. LOS is a qualitative measure which is intended to relate the quality of traffic service on a particular roadway to a given traffic flow rate. In LOS-based traffic analyses, traffic facilities are rated by letters A, B, C, D, E and F, with an A rating denoting the best quality of service and an F rating denoting the worst quality of service.

The facilities are evaluated based on certain measures of effectiveness, including speed of travel, travel time, traffic congestion and density, and delay. In short, automobile delay is the key focus for the LOS analysis, which is concerned with how fast and how many cars can move through a particular traffic facility in a fixed amount of time. The standard method to mitigate traffic impacts identified by an LOS-based analysis has been to build additional roadway capacity through new road or road widening projects.

Critics of the LOS method of traffic analysis have argued that by focusing on automobile delay alone, state and local agencies have encouraged urban sprawl over infill development and have done little to address or mitigate the real environmental impacts of traffic, including air quality impacts. Pedestrians and bicyclists have expressed concern that LOS prioritizes cars over pedestrian and bike safety, and discourages smart travel and use of public transit. These concerns have given rise to a movement throughout California to eliminate automobile delay and LOS-based analyses as the method by which traffic impacts are studied in the state.

In 2013, Governor Jerry Brown signed Senate Bill 743, which created a process to eliminate LOS-based analyses and fundamentally change the way traffic impacts are analyzed in California. The legislation required development of an alternative to LOS which would "promote the reduction of greenhouse gas emissions, the development of multimodal transportation networks, and a diversity of land uses." Since the adoption of SB 743, the state Office of Planning and Research (OPR) has been evaluating possible metrics to replace LOS.

In January 2016, OPR released a final draft proposal for public review and comment. The proposal includes a recommendation that the LOS-based analyses be replaced by a vehicle miles traveled (VMT) method of transportation analysis. In contrast to the delay and congestion-based LOS analysis, VMT analysis measures the amount and distance a particular project might cause people to drive, including the capacity of and number of passengers utilizing individual vehicles. This proposal will be forwarded to California's Natural Resources Agency for a formal public rulemaking process.

The movement from LOS to VMT is not occurring only at the state level in California. The City and County of San Francisco recently became the first major city to endorse the VMT based methodology. Just this month, the City's Planning Commission voted to immediately implement changes to its citywide transportation impact analyses rather than wait for the eventual adoption of the new state standards. The City of Pasadena previously made a similar change.

While California has been at the forefront of the shift to VMT, other states through their Departments of Transportation have considered similar methodology for study of traffic impacts. The State Smart Transportation Initiative (SSTI), which is housed at the University of Wisconsin, is actively promoting transportation practices that advance environmental sustainability and equitable economic development, while maintaining high standards of governmental efficiency and transparency. SSTI has authored a leading white paper on the shift to VMT-based analyses.

The shift to VMT-based transportation impact analysis has not been without controversy or criticism. Common concerns include the ability of such an analysis to adequately analyze and mitigate traffic impacts, uncertainty in the scope and nature of the proposed analysis, and the potential for increased litigation. In California, the formal state rulemaking process will offer additional opportunities for public review and comment on this significant policy change. For additional information, you can visit: https://www.opr.ca.gov/s_sb743.php.

This article was originally published in Environmental Leader, March 21, 2016.