重新审视公共资本需求：基于效率和拥堵效应的增长最大化投资分析

Revisiting Public Capital Need An Analysis of Growth-Maximizing Investment withEfficiency and Congestion EffectsPublic Disclosure Authorized Santiago HerreraChristophe HurlinHironobu Isaka Economic Policy Global DepartmentDecember 2025 A verified reproducibility package for this paper isavailable athttp://reproducibility.worldbank.org,clickherefor direct access. Policy Research Working Paper11272 Abstract This paper estimates growth-maximizing levels of publiccapital and investment across countries using a structuralframework that accounts for three critical features: publicinvestment efficiency, human capital levels, and congestioneffects. A harmonized panel data set covering 166 countriesover 1960–2024 was assembled to estimate public capitaloutput elasticities for the entire sample and for countriesclustered by income group. These estimates are used to cal-ibrate an endogenous growth model yielding closed-formexpressions for the optimal public investment-to-outputratio. The analysis finds a public capital output elastic-ity of around 0.20, which implies that countries investslightly below their growth-maximizing levels. For the fullsample and a homogeneous elasticity of public capital, theobserved investment-to-output ratio averages 4.6 percent,significantly below the growth-maximizing level of 5.4 per-cent. The shortfall in aggregate investment becomes even more significant when using higher output elasticities ofpublic capital. The aggregate results show considerable het-erogeneity: public investment in advanced and emergingeconomies is, on average, 1.5 to 1.8 percent of gross domes-tic product below the growth- maximizing levels, while inlow-income countries the gap is far wider at 3.2 percent ofgross domestic product. Improving public expenditure effi-ciency can enable countries to increase investment withoutcompromising fiscal sustainability. The analysis also findsthat countries with large resource revenues, greater revenueand expenditure volatility, weaker fiscal governance, andlower institutional quality are more likely to have excessivelevels of public investment. These results provide bench-marks for assessing public investment gaps and underscorethe importance of expenditure efficiency, high-quality fiscalgovernance, and robust public institutions in achievingoptimal levels of public investment. The Policy Research Working Paper Series disseminates the findings of work in progress to encourage the exchange of ideas about developmentissues. An objective of the series is to get the findings out quickly, even if the presentations are less than fully polished. The papers carry thenames of the authors and should be cited accordingly. The findings, interpretations, and conclusions expressed in this paper are entirely thoseof the authors. They do not necessarily represent the views of the International Bank for Reconstruction and Development/World Bank andits affiliated organizations, or those of the Executive Directors of the World Bank or the governments they represent. RevisitingPublic Capital Needs:An Analysis of Growth-Maximizing Investment with Efficiency and Congestion Effects1 Santiago Herrera†Christophe Hurlin‡Hironobu Isaka† Keywords:Public capital, Infrastructure investment, Long-term growth model, Investment efficiency. JEL codes: O40, O47, E22, H54. Introduction Since the seminal contributions ofAschauer(1989) andBarro(1990), public capital has been widely recognizedas a fundamental driver of long-run economic growth. By enhancing connectivity, improving the delivery of publicservices, and boosting the productivity of private inputs, infrastructure investment can crowd in private activityand facilitate structural transformation. However, despite decades of theoretical development and empiricalinvestigation, the question of whether countries invest too much or too little in public capital remains open andactively debated both in academic and policy circles. The empirical literature has concentrated on estimating the output elasticity of public capital within a production-function framework. Most studies find a positive and statistically significant contribution of public capital tooutput, although estimates vary across countries, sectors, and methodologies (Bom and Ligthart,2014). However,quantifying this elasticity is only a preliminary step toward formulating fiscal policy. A more relevant operationalquestion concerns the optimal level of public capital and the investment effort required to sustain it. Such normativebenchmarks are essential for guiding infrastructure strategies and evaluating whether current levels of publicinvestment are consistent with long-run growth objectives. In this context, we estimate the growth-maximizing levels of public capital and public investment using a structuralapproach.2We explicitly account for three critical dimensions that are often overlooked in the empirical literature:(i) the efficiency of public investment, (ii) the role of hum