Southern California traffic is famously congested. Because population and vehicle traffic have increased at rates that greatly exceed growth in highway capacity, stifling congestion has burdened the region’s economy and quality of life for its residents. Local officials estimate that every 10 percent decrease in Los Angeles-area congestion will create 132,000 jobs. To address these challenges, the region’s longterm transportation plans call for more than $100 billion of investments in transit as well as more than $80 billion in highway improvements (not including operations and maintenance). Federal funding and permitting of these projects will be placed at risk if the region is unable to demonstrate that they will not contribute to violations of EPA’s tightened standard.