Traffic Volumes at Regional Gateways

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

Traffic Volumes at Regional Gateways

Definition: 
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 nation’s largest and most vibrant metropolitan areas, and every day, over 600,000 vehicles pass into or out of the region from adjacent areas. Beyond commuters heading for robust job centers like the Tri-Valley, Silicon Valley and San Francisco, regional gateways serve commercial trucks, buses and recreational travelers. Over half of those 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 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. In fact, between 2000 and 2006, traffic volumes jumped by 20 percent. Yet as of 2014, daily gateway traffic volumes remain 4 percent below 2006 levels. While volumes ticked upward in 2014 for the second year in a row – going above the 600,000 mark for the first time since 2008 – the rate of growth is significantly slower than in the 1990s.

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. While traffic in the latter corridor serving the Altamont Pass has been growing at a faster rate this decade, a spike in traffic between the Bay Area and Sacramento in 2014 allowed the I-80 corridor to widen its lead as the busiest interregional gateway. 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 to the South Bay.

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Historical Trend for Traffic Volumes at Regional Gateways

 
 
 
Sources: 

California Department of Transportation: Annual Traffic Volume Reports (1992-2014)

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.