Increased real productivity might occur due to public spending, but its less likely that it was in the 1800s, if the Govt "bet" on that bridge does not payoff, then is each dollar printed to bet on it is diluting the value. I wouldn't trust the public sector to correctly allocate the resources to increase the real economic output over the private sector, for self evident historical lessons. And now that the low fruit has been taken, they might be tempted to build bridges to nowhere https://www.alaska.org/detail/bridge-to-nowhere