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Sacramento Implements SB 743 with VMT Data

The Sacramento Area Council of Governments found the VMT data it needed to implement legislative changes to transportation impact studies.


In 2020, California began implementing SB 743, a law that changed the way the state’s public agencies assess the environmental impacts of new transportation projects. While planners have traditionally focused on how a project might affect traffic congestion, SB 743 instead requires planners to study how a project will affect the amount of vehicle miles traveled (VMT) in a region; that is, if it will add to the amount of driving that takes place on the state’s road network. The Sacramento Area Council of Governments (SACOG) needed new tools to implement this change.


Per SB 743 requirements, SACOG has to estimate VMT for travel occurring outside of its jurisdiction, but its existing Travel Demand Model did not account for those trips.


SACOG worked with Replica to generate region-wide activity-based travel models for multiple seasons. SACOG uses the detailed trip tables from these models to better understand existing conditions before investing in large-scale infrastructure and development projects. The data allows SACOG to better understand the VMT patterns of its residents and of its road network, and to calculate VMT for trips that occur outside of its region. They also use it to help understand the breakdown of VMTs across different trip purposes, including (but not limited to) commuting.

Key Insight & Impact

“The beauty of the [Replica] platform is its ability to be nimble,” says Warren Navarro, GIS analyst at SACOG. “We have the utmost confidence with regards to using this platform and providing the service to our member jurisdiction.”

SACOG performed an extensive assessment of Replica’s data before deciding to incorporate it into their existing workflow. They validated Replica’s synthetic population, transit ridership, and traffic volumes against the ground truth data they provided. Extensive reasonableness checks on link speeds, VMT, mode share, and employment data gave SACOG the confidence to proceed with Replica.