Investing great John Bogle, founder of The Vanguard Group and champion of the index fund, believes our nation's retirement system is headed for a serious train wreck. Anyone who looks objectively at the evidence would have to agree with him.

I recently examined several outstanding research studies on the state of retirement savings in America, and here are some of the alarming facts that I discovered:

Only 42% of private sector workers age 25 to 64 have any pension coverage in their current job. That's lower than the 50% who had pension coverage back in 1979. (Source: Center for Retirement Research) 30% of workers in a 2012 study reported that they had less than $1,000 in savings and investments. (Source: Employee Benefit Research Institute) A 65-year-old couple retiring in 2012 is estimated to need $240,000 to cover medical expenses throughout retirement. (Source: Fidelity Investments) Just 14% of American workers are very confident they will have enough money to live comfortably in retirement. (Source: Employee Benefit Research Institute) Only 16% of American workers are very confident that their investments will grow in value. (Source: Employee Benefit Research Institute) Half of current retirees surveyed say they left the work force unexpectedly as a result of health problems, disability, or getting laid off. If you think you'll just "work forever" instead of planning for retirement, you may want to think again. (Source: Employee Benefit Research Institute) For a low earner retiring at 62 -- Social Security replaces 40% of pre-retirement earnings. This is unlikely to provide for a comfortable retirement. (Source: Employee Benefit Research Institute) Nearly 75% of retirees have not saved enough and said they would save more if they could do it all over again. (Source: Health and Retirement Study) More than one-third of all households end up with no employee-sponsored retirement plan at all during their entire work lives and others, who move in and out of coverage, end up with inadequate 401(k) balances. (Source: Center for Retirement Research) At age 65 and above, Social Security benefits provide more income than any other source for over 60% of households, regardless of marital status. With an average monthly benefit of $1,230 for retired workers, this indicates that a lot of retirees must be struggling. (Source: Health and Retirement Study) One-third of households end up entirely dependent on Social Security; for low earners that portion is 75%. (Source: Center for Retirement Research) 21% of workers covered by 401(k) plans choose not to participate. (Source: Center for Retirement Research) A typical worker should accumulate about $363,000 by the time he or she retires. According to the Fed, a typical household approaching retirement had 401(k)/IRA balances of only $120,000 in 2010, far short of the projected amount for the individual. (Source: Center for Retirement Research) In 2002, the mean household wealth of married couples reporting excellent health was approximately three times that of married couples reporting poor health (an average of $500,000 compared with $164,000). (Source: Health and Retirement Study) Average household net worth was $31,000 when both partners were in poor health but more than $400,000 when in excellent health. (Source: Health and Retirement Study). 60% of workers report that their total household savings and investments, excluding the value of their home and any defined benefit pension, is less than $25,000. (Source: Employee Benefit Research Institute) 56% of workers report that they have not attempted to calculate how much money they will need to have saved for a comfortable retirement. (Source: Employee Benefit Research Institute)

These are just some of the facts that are included in the studies referenced above. For more detail, I'd encourage you to read the studies in their entirety.

One big takeaway is that many Americans are saving far too little for their retirement. And many of those individuals who are saving are making costly errors that result in poor investing returns. Bogle believes that our society tends to be wired for short-term thinking when it's long-term strategies that are most needed right now in tackling this retirement crisis.

In order to better understand this crisis, we've put together series of articles that take a deeper look at the important challenges facing our retirement system. In "5 Huge Myths About Social Security," Ilan Moscovitz examines our widely misunderstood Social Security system. In another commentary, Sara Murphy explores the question of whether 401(k) plans are a failed experiment. Finally, in a concluding commentary, I put forward some ideas for possibly improving our overall retirement system. We hope you enjoy the series!

To read all of the articles in this series, click on the following links: