The age-old tradition of packing up the car and heading to the beach with the family might becoming a thing of the past.

A new study finds that many workers are opting out of taking all of their vacation time. More than half of U.S. workers ended last year with an average of 11 unused vacation days.

Workers' reasons, according to a survey by Careerbuilder.com, include too much to do, fear of losing their job and not making enough money.

The survey also finds Americans are taking shorter vacations, and when they do go out of town, they're staying connected via laptops and cell phones. In fact, one-third of bosses say they expect workers to check in while on vacation.

Managers are more likely to take time off, with 81 percent planning to take a vacation this year, compared with just 65 percent of full-time employees.