Nearly six percent of freeway miles driven in the Bay Area are affected by traffic congestion. While a relatively small share of overall regional travel, this figure has grown in recent years. In fact, 2015 was the third year in a row that traffic congestion reached a record high. This growth in congestion has been driven by worsening conditions in San Francisco, Santa Clara and Alameda counties. Still, as this data makes clear, the effect of regional traffic congestion is much more limited than most drivers might think.
For the first time on record, San Francisco topped the list of the region’s counties with the greatest share of miles driven in congestion. At 8.6 percent in 2015, it surpassed Alameda County, which has historically been the most congested in the Bay Area. The latest data for these counties, when considered alongside those of neighboring counties, reflect slower freeway speeds and increasing congestion in the urban core. On the other hand, in the more northerly counties of Sonoma, Napa and Solano, drivers spend very little time in congested conditions. These counties have seen little-to-no growth in congestion over the past decade.