FOR MOST OF US, a toll road is just another expense. But for a family with vast resources and a long investment horizon, it can be something quite different: a source of income.

In growing numbers, rich families are investing in infrastructure, putting their money to work on remote mountaintops, bustling harbors and across deserts the world over. This broad category covers the structures and systems needed to keep economies running and growing. So think highways, public transit, power plants, telecom backbones