How To Run A US Infrastructure "Bank"

One of the perversities of the US democratic political cycle is that when the economy is doing well, governments tend to have higher revenues and spend more on infrastructure and when there is a recession, governments tend to reduce spending on infrastructure because these are durable goods that could be built at any time.  This is particularly true of state and local governments.  But this is exactly backwards from the ideal.  The government should borrow more money when interest rates are low (during recessions) and save more money when interest rates are high (during expansions).  Furthermore, the government should spend more money when costs are low and unemployment is high (during recessions) and spend less money when costs are high and unemployment is low (during expansions).  We need this to be more automatic and a way to do that would be to create an infrastructure "bank" which sets infrastructure spending/savings/borrowing according to the costs of creating infrastructure.  When costs are low (during recessions) the bank would spend more and when costs are high (during expansions) the bank would spend less.
This is how markets work and it would be easy to set up an idealized supply and demand graph for how the bank would work.  Congress would determine the long-run demand function and the "bank" would just determine the spending or savings. [draw supply and demand graph here] When the supply of market savings goes up, interest rates go down and the bank should spend more.  When the supply of construction workers goes up, the price of construction goes down and the bank should spend more.  It would need to be set up as a quasi-independent institution like the Fed with long-run goals that are set by congress but with day-to-day independence in its operations.