A note on changes in transportation patterns related to COVID-19: The traffic volume data presented on Vital Signs represent typical transportation activity through 2017, the most recent year for which data are available. While transportation patterns today have been impacted by COVID-19 and the statewide Shelter in Place order, data on 2020 traffic volumes at regional gateways will not be made available by Caltrans until Fall 2021.

Traffic Volumes at Regional Gateways

How do commuters from outside the Bay Area affect traffic here?

Traffic Volumes at Regional Gateways

Traffic volumes at regional gateways refers to the number of vehicles crossing county boundaries on a typical day to enter or exit the nine-county San Francisco Bay Area.

The Bay Area is one of the largest and most vibrant metropolitan areas in the nation. Every day, over 600,000 vehicles enter and exit the Bay Area. In addition to commuters heading to job centers like the Tri-Valley, Silicon Valley and San Francisco, regional gateways serve commercial trucks, buses and recreational travelers. Over half of these travelers use just two regional gateways: Interstate 80 connecting Solano County and Yolo County, and Interstates 580 and 205 connecting Alameda County and San Joaquin County.

Regional Performance
The region’s strong economy has contributed to a spike in traffic from neighboring counties.

The Great Recession had a profound effect on interregional traffic volumes, halting two decades of steady growth. Up until 2006, the Bay Area witnessed significant growth in traffic entering from neighboring counties, contributing to regional congestion challenges. The recession reversed this trend from 2006 through 2012, but the resurgent Bay Area economy has since powered growth in traffic for three years in a row. Although still below the 2006 peak, 2015 was the second-highest year on record for daily gateway traffic volumes.

Two regional gateways account for over half of all traffic entering or exiting the Bay Area: Interstate 80/State Route 113 in Solano County and Interstate 205/Interstate 580 in Alameda County. A spike in traffic between the Bay Area and Sacramento beginning in 2014 caused the I-80 corridor to widen its lead as the busiest interregional gateway. Meanwhile, traffic in the Interstate 205/Interstate 580 corridor has also been growing at a faster rate this decade due to higher volumes over the Altamont Pass. The region’s next-busiest gateways are U.S. Route 101 connecting Santa Clara and San Benito counties, and State Route 17 connecting Santa Clara and Santa Cruz counties. Traffic volumes are similar at these two gateways, but given relatively slow growth in Santa Cruz and decades of stable or declining traffic volumes in the Route 17 corridor, U.S. Route 101 may soon overtake Route 17 as the primary interregional gateway in the South Bay.

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Historical Trend for Traffic Volumes at Regional Gateways


California Department of Transportation: Annual Traffic Volume Reports (1992-2015)

Image: Flickr (Creative Commons license), Photographer: Chris Potako, https://www.flickr.com/photos/51771794@N07/5964916775

Methodology Notes: 

Traffic counts reflect average annual daily traffic (AADT) counts at all state highway gateway points - entry/exit points to the nine-county San Francisco Bay Area. When the county line data was not available in the traffic volume reports, the closest intersection or interchange was used as a proxy for traffic volumes at the county line.