(Bloomberg) -- A retirement savings wave that has beenrolling stealthily across corporate America is gaining momentum.Some 68 percent of large U.S. companies now automatically enrollemployees in 401(k) plans, up from 58 percent two years ago,according to a new survey.

Three-quarters of those employers bump up worker savings ratesautomatically every year, and many continue until savings rates hit10 percent and beyond—or until, presumably, the employeescreams.

That may seem a little heavy-handed, but a retirement planthat's largely on autopilot can make inertia work for, rather thanagainst, savers.

After all, saving 10 percent of one’s salary doesn’t even meetthe minimum suggested by experts such as Morningstar’s head ofretirement research, David Blanchett. He puts the minimum at 12percent, and says a good rule of thumb is more like 15 percent.Some of that should come from your employer’s matchingcontributions.

A biennial survey by benefits administrator AlightSolutions reached 333 big U.S. employers representing 10 millionworkers and $775 billion in retirement assets.

Among some of the positive signs in the survey: A third ofcompanies are setting the default savings rate for workersautomatically enrolled in their plans at 6 percent or more ofsalary.

The survey still found the common, inadequate savings rateof 3 percent at 37 percent of employers.

Here are highlights from the report:

Thirty-four percent of the companies offer employer stockas an option in plans.

As an asset class, it made up 11 percent of the total, thesame percentage held in stable value funds. "The concentrationin company stock is going down, but it's still a pretty largeasset class," said Rob Austin, director of research atAlight.

Thirty-one percent of plans that offer employer stockrestrict how much of a new employee’s contributionscan go into the stock or limit it to a chunk of the overallbalance. That limits how much of a potential hit a worker can takefrom holding such a concentrated position in a stock.

Assets in large-cap stocks in the plans surveyed roseto 23 percent of the total, from 21 percent in 2015, whilemoney in stable value funds fell from 14 percent to 11 percent.

Employer stock slid from 13 percent to 11 percent, and assetallocations to intermediate-term bonds rose to to 7 percent, from 5percent. Allocations to the 14 other asset categories had the samepercentage figures as in 2015.

Three quarters of companies offer a Roth 401(k) option, upfrom 58 percent two years ago and 11 percent a decade ago.Over the past decade, the percentage of plans offering managedaccounts from an outside vendor as an option has risen from 11percent to 58 percent.

These accounts offer a more personalized assetallocation for an extra fee. Just 14 percent of employees, onaverage, opted for a managed account in 2017, down from 16 percentin 2015 and 20 percent in 2013.

The biggest change in the asset classes available to planparticipants was a jump to 17 percent, from 12 percent in 2015, inthe percentage of plans offering global equity investments.

The asset classes that the plans were most likely to add weretarget date/target risk funds (27 percent), midcap equity (23percent), and stable value (18 percent).

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