But some national governments, particularly the U.S. and other Western countries, are trimming their public-works funding, measured as shares of gross domestic product, because of budget worries, the report adds.

In the U.S., infrastructure accounts for about 1.7% of GDP, the lowest level in 20 years, says the report, citing data from the Federal Reserve Bank of St. Louis.

Some Asian countries’ government infrastructure funding levels are much higher—8.5% of GDP for China and 4.7% for India—but S&P says those percentages probably will fall in the longer term.

The study also says the advantages of infrastructure investments include higher returns than on government bonds or corporate bonds with similar ratings; an ability to match long-term assets with long-term liabilities; relatively lower default totals and higher recovery rates than with corporate bonds.

But S&P also notes that many insurers and pension funds are wary about investing in infrastructure for reasons that include a reluctance to take on construction risk as well as political and regulatory risk.

Some private investment will continue to go into public-private partnerships, according to S&P. It mentions as examples Canada’s five-year renewal of its P3 fund last year and the United Kingdom’s Private Finance 2 plan.

In the U.S., S&P notes that states such as California, Indiana, Texas and Virginia have been active in P3s.