In such circumstances, governments considering a proposal to build, say, a new highway, should regard this as an ideal time. If the highway will cost $1 billion, last indefinitely with regular maintenance and repairs, and yield projected annual net benefits to society of $20 million, a long-term real interest rate of 3% would make it nonviable: the interest cost would exceed the benefit.
在这样的环境下，政府如要考虑建设（比如）一条新高速公路可谓正逢其时。如果高速公路成本是10亿美元，永久需要定期维护和微小，预计每年产生2,000万美元的净社会效益，那么如果长期真实利率超过3%，该项目将难以为继：利息成本将超过收益。但如果长期真实利率为1%，政府应该借钱修建这条公路。这是可靠的投资。