With the adoption of Senate Bill (SB) 743, the State of California changed the method of traffic analysis required through the California Environmental Quality Act (CEQA) for publicly- and privately-initiated projects. The law changed the way local jurisdictions, like the County of San Diego (County), analyze transportation impacts from development projects and identify mitigation measures to reduce those impacts. SB 743 became effective on July 1, 2020.

The San Diego Board of Supervisors adopted the Transportation Study Guide (TSG) which established VMT thresholds and screening criteria on Sept 28, 2022. The TSG can be found here: https://www.sandiegocounty.gov/content/sdc/pds/SB743.html

The previous practice of evaluating traffic transportation impacts used on-road congestion or level of service (LOS). SB 743 requires the amount of driving and length of trips – as measured by "vehicle miles traveled" or VMT – be used to assess transportation impacts on the environment for CEQA review. These impacts will be reduced or “mitigated” by options such as increasing transit, providing for active transportation such as walking and biking, and participating in mitigation banks.

VMT per Resident

VMT per Resident is the metric used for residential projects and is established by summing up total daily VMT generated by residents of a geographic area and dividing by the population of that geographic area. Total daily VMT includes all trip tours made by residents: home-based and non-home-based trip tours (i.e., all VMT for a resident for the entire day regardless of trip purpose or origin/destination).

VMT per Employee

VMT per Employee is the metric used for employment projects (e.g., office, commercial, retail) and is established by summing the work related total daily VMT generated by resident employees of a geographic area and dividing by the number of employees of that geographic area. Total daily VMT includes all work tours made by employees (this includes an employee’s commute and any other work-related travel such as going to lunch or to a meeting).

VMT per Service Population

VMT per Service Population is the metric used for retail projects that are not considered locally-serving. It is established by dividing the total VMT with at least one trip end in a geographic area by the population plus employment of that geographic area. The total VMT includes all internal VMT, internal to external, and external to internal VMT (in other words all VMT regardless of geographic boundaries). Since this metric combines VMT for residents and employees and reflects how accessible all land uses are (for example, geographies with higher density, more shopping, and more jobs will have lower VMT per Service Population).