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.