capital. Despite this unique nature, public capital investment, used in the production process of nearly every sector, is not sufficient on its own to generate sustained economic growth. Thus, rather than the ends, public capital is the means. That is, instead of being seen as intermediate goods used as resources by businesses, public capital should be seen as goods which are used to make the final goods and services to consumers-taxpayers. Note that public capital levels should not be too high that it leads to financing costs and high tax rates issues which will negate the positive benefits of such investments. Moreover, infrastructure services carry the market-distorting features of pure, non-rival public goods; network externalities; natural monopolies; and the common resource problem such as congestion and overuse. Empirical models that attempt to estimate the public investment and economic growth link involve a wide variety including: the Cobb-Douglas production function; a behavioral approach cost/profit function which includes public capital stock; Vector Auto Regression (VAR) models; and government investment growth regressions. These models nonetheless contend with reverse causality, heterogeneity, endogeneity, and nonlinearities in trying to capture the public capital and economic growth link. New Keynesian models, though, analyze the effect of government spending through the supply side rather than traditional Keynesian models that analyzes it through the demand side. Therefore, a temporary surge of infrastructure investment yields an expansion of output, and vice versa that dwindling infrastructure, like in the 1970s, hamper longer-term movement in productivity. Furthermore, new research on regional growth (as opposed to national growth with GDP) shows a strong positive relationship between public capital and productivity. Both fixed costs and transport costs lower with expanded infrastructure in localities and the resulting cluster of industries. As a result, economic activity grows along its pattern of trade. Therefore, the importance of regional clusters and metropolitan economies comes into effect. Social benefit Beyond economic performance, public capital investment yields returns in quality of life indicators such as health, safety, recreation, aesthetics, and leisure time and activities. In example, highways provide better access and mobility for increased discretionary time and recreational outlets; mass transit can improve air quality with reduced number of private vehicles; improved municipal waste facilities reduces toxic groundwater contamination and better green space aesthetics such as parks; expanded water facilities aids in health and sanitation and environment such as reducing odor and sewer overflows. Furthermore, infrastructure adds to community ambience