North Carolina and South Carolina are neighboring southeastern states, but despite their similar climate and terrain, their costs of highway projects are vastly different. For repaving work begun in 2018 or 2019, South Carolina’s Department of Transportation spent an average of $375,500 per mile, more than twice as much as its northern neighbor.

That discrepancy is one of many intriguing findings about state DOTs uncovered by Zachary Liscow, a professor at Yale Law School who is trained as an economist as well as a lawyer. For more than a decade, Liscow has examined how state DOTs pay for infrastructure, and he’s reached a series of striking conclusions about why their costs have risen over time, albeit at very different rates. He also offers suggestions about ways transportation agencies can get more bang for taxpayers’ dollars.