More 401(k) retirement plan participants are turning their portfolio construction over to a professional, according to Vanguard’s annual 401(k) report.

In 2012, 36% of all participants in Vanguard retirement plans invested their assets in a professionally managed investment option, more than double that did so in 2007. About one in four (27%) were invested in a single target-date fund, 6% held a single traditional balanced fund, and 3% used a managed account advisory program. Vanguard estimates that 55% of all participants will be entirely invested in a professionally managed investment option by 2017.

The shift in responsibility for investment decision-making away from participants to investment and advice programs that have been vetted by employers as part of their fiduciary obligations is an important trend in the potential future financial security of retirees, said Jean Young, co-author of the report, How America Saves.

According to the report, average account balance rose by 10% in 2012, to $86,212, reflecting the effect of both ongoing contributions and market returns.

The average participant contribution or deferral rate was 7% in 2012, down slightly from the peak of 7.3% in 2007. One-third contributed less than 4%. When taking into account both contributions made by participants and employers to participants’ account, the average total savings rate was 10.5%.

Vanguard recommends an annual savings rate of 12% to 15%, depending on income level. “While we are seeing good news overall in the retirement planning habits of participants, many Americans are still not saving enough for the future,” Young said in a statement.