It's important to note that the Federal reserve normally controls the overnight rate, and let the market determines the interest rate for other durations (eg. 3

It's important to note that the Federal reserve normally controls the overnight rate, and let the market determines the interest rate for other durations (eg. 30Y). That changed with the introduction of Quantitative Easing where it reduces the interest rate over the entire yield curve. In other words, even through the overnight rate is 0%, you could still push down the interest rate down for bonds of a longer maturity, and that'll further stimulate the economy.