Student loans debt has been steadily rising in recent years, at rates far in excess of the rates of growth in overall credit to the U.S. households. However, the data shows conclusively, that the degree of leverage risk implied by growing student debt is now out of control. Here are two charts, referencing the levels of student debt to earnings and employment costs since 1Q 2005:
Source: Bloomberg

Source: my own calculations based on data from Fred database

In very simple terms, adjusting for labor compensation to college graduates, student debt growth rates since 1Q 2005 have exceeded the growth rates in returns to college degrees. The rate of this excess, cumulated from 2005-2006 period is around 2.5 times. In other words, student debt has grown 2.5 times more than the growth rate in college degree-holder's labour compensation.