In 2017, President Donald Trump was considering a major increase in federal government spending on infrastructure: building and repairing bridges, highways, rail lines, and subways. An article in the Economist argues that: "Just as economists talk of 'negative externalities' (from, say, pollution), infrastructure can have positive externalities that are not captured by investors but will benefit society." Source: "Are Big Infrastructure Projects Castles in the Air or Bridges to Nowhere?" Economist, January 16, 2017. Explain what positive externalities might exist from infrastructure spending