Many people have asked, if the US Economy is growing then why haven't longer term interest rates gone up? The chart above helps to answer that question. If you are looking to invest in safe assets around the world the US Treasury is very attractive. If I gave you a choice which bond would you rather buy? A US Treasury at 2.00% (currently) or the German Bund at 0.50%? Most people believe that the value of the US Dollar will continue to increase versus other currencies. Which makes owning the US Treasury even more attractive.
As long as this situation continues, I think that US Interest rates will remain low for longer. The good news is that this does provide a benefit to the US economy. Mortgage rates remain low, and companies can continue to issue debt at low levels.