Revisiting The Optimal Stationary Public Investment Policy In Endogenous Growth Economies

One part of the literature on endogenous growth concerns models where public infrastructure affects the private production process. An unsolved puzzle in this literature concerns observed public investment-to-output ratios for developed economies, which tend to fall short of theoretical model-based optimal ratios. We reexamine the optimal choice of public investment in a more general framework. This setting allows for long-lasting capital stocks, a lower depreciation rate for public capital than for private capital, an elasticity of intertemporal substitution that differs from unity, and the need to finance a nontrivial share of public services in output. Given other fundamentals in the economy, we show that the optimal public investment-to-output ratio is smaller for low-growth economies, for economies populated by consumers with low preferences for substituting consumption intertemporally, and when public capital is durable. For a calibrated economy, we show that a combination of these factors solves the public investment puzzle.