As the summer vacation season winds down, consider this: Americans report they are not happy at work.

Employees in the United States find their workplace to be physically and emotionally taxing environments where they face unstable work schedules, unpleasant and potentially hazardous working conditions, and social environments that rival snarky junior high schools, according to a study by the Rand Corp., Harvard Medical School, and UCLA that was released Monday.

Researchers queried 3,066 adults about conditions in the workplace.

Twenty-five percent of employees said that they had too little time to do their jobs and that the work spilled over into their personal life. About 50 percent of those surveyed said they worked during their free time to meet workplace demands. One-third of workers say they are unable to adjust work schedules for personal matters.

And forget telecommuting. Seventy-eight percent of workers said they must be at their workplace during regular business hours.

Only 38 percent of those surveyed said their job offered good possibilities for advancement.

One in five workers said they faced a hostile or threatening social environment at work. Younger women are most likely to experience unwanted sexual attention, while younger men are more likely to experience verbal abuse, the study reported.

In spite of the pessimistic response, more than 50 percent of people described their bosses as supportive and felt that they had good friends at work.

Yet, as unhappy as those surveyed reported to be, more than half did not take the paid time off they were due.

That would be a collective 662 million vacation days, according to Project Time Off, a travel trade group that tracks how much time Americans spend on vacation.

One reason: "People don't want to return to mountains of work," said Katie Denis, chief of research and strategy at Project Time Off.

"Work is no longer a marathon, but a series of sprints," she said, "and you have to have recovery time."

Employers can create a better environment that encourages employees to take the time they are due. When workers do take time off, they come back renewed and are more productive, she said.

On average, Americans miss three personal events a year because of work, with most of those events being for their children, she said.

"That is stuff you can't get back," Denis said, adding that missing family events has negative implications in the long run.

In Pennsylvania, 45 percent of workers don't use all their vacation time. In New Jersey, 49 percent leave time on the table, according to Project Time Off.

Denis suggests planning vacations in advance and not leaving unused days until December, when workers are less likely to get time off.

"Plan it now," she said, "before it is too late."