Roughly half of U.S. workers have access to an employer-sponsored retirement plan. The financial services industry has argued that people who lack workplace plans can easily open an individual retirement account. That's true, but few investors do so. Only about 14 percent of investors regularly contribute to their IRAs, according to a new report from the Center for Retirement Research at Boston College. The remaining assets in IRAs are from when employees roll over their 401(k) plans and other workplace retirement plans. "IRAs were intended to help people save more for retirement; instead, they have become a holding place for money that was originally in 401(k) plans," said Geoffrey Sanzenbacher, a research economist at the center.

Investors have parked a massive amount of money in IRAs, which hold more than $7.8 trillion in assets, according to the Federal Reserve. That exceeds the more than $5.7 trillion in 401(k) plans and other workplace retirement plans, as well as the $3.3 trillion held in traditional pension plans in the private sector. Not every investor is forgetting about their IRAs. The center found, using data from the U.S. Census Bureau, that frequent contributors fall into three distinct groups: "dual-income super-savers," "frugal breadwinners" and the self-employed. Among the investors who frequently contribute to IRAs, roughly 43 percent were super-savers, another 43 percent are frugal breadwinners, and 14 percent were self-employed. Nearly 66 percent of the super-savers, who had an average annual income of $149,149, and more than half of the frugal breadwinners, with an average annual income of $59,527, also contributed to their employer's 401(k) plans in addition to their IRAs. Since the self-employed rarely have access to a 401(k), most were saving through an IRA as an alternative to an employer-sponsored plan, the center found.

"The lower participation in IRAs is a matter of behavioral finance, " said Jeffrey Levine, chief retirement strategist at Ed Slott and Co. in Rockville Centre, New York. Unlike with workplace retirement plans, people have to find an IRA provider, have enough money to open an IRA and figure out how they will invest it, he said. Workers with 401(k) plans can automatically invest with payroll deductions and often receive some help from their employers in selecting investments or are defaulted into decent options. If an employer offers matching contributions, it makes sense for workers to contribute to their 401(k)s before an IRA, Levine said. IRAs also have lower contribution limits than 401(k) plans. This year, you can only contribute $5,500 to a traditional or Roth IRA and $1,000 more if you are age 50 or older. The maximum 401(k) contribution limit is $18,000 per year. "But people underestimate what $5,500 in annual contributions can do over time," Levine said.

What's been clear from the data is that automatic payroll deduction works. David Certner AARP's legislative counsel