When the highway overpass on I-95 north of Philadelphia came down last month, it wasn’t due to the usual poor maintenance or political dysfunction that are often blamed for America’s crumbling infrastructure. A gasoline truck lost control and crashed into the underpass, and the ensuing fire brought the short bridge down. All of a sudden, one of Philadelphia’s and the regional economy’s most important arteries for commuters and shipping was out of commission. The downed stretch of highway typically had more than 150,000 daily crossings, including 14,000 trucks.