WASHINGTON — Barriers went down at National Park Service sites and thousands of furloughed federal workers began returning to work across the country Thursday after 16 days off the job due to the partial government shutdown.

The Office of Personnel Management announced that workers should return to work on their next regularly scheduled work day — Thursday for most workers. Nationwide, hundreds of thousands of workers have been furloughed since the shutdown began Oct. 1. The office encouraged agencies to be flexible for a smooth transition by allowing telework and excused absences in some cases.

In Washington, the U.S. Capitol’s visitor center planned to resume tours Thursday, the United States Holocaust Memorial Museum was reopening, and the Smithsonian Institution proclaimed on Twitter, “We’re back from the (hashtag)shutdown!” The National Zoo was set to reopen Friday, though its popular panda cam was expected to be back online Thursday.

“Just to be able to get back to serving the public is so important,” said Greg Bettwy as he prepared to return to his job with the Smithsonian’s human resource department. Bettwy said he watched his spending carefully during the shutdown — choosing store brands at the grocery store and forgoing a trip to see a Penn State football game.

The returning workers’ presence will be felt on the roads and rails in the Washington region, where commutes have been less crowded over the past two weeks. The regional transit agency, Metro, reported a 20 percent drop in ridership when the shutdown began and has said it lost a few hundred thousand dollars each day.

Workers began filing in well before dawn at the U.S. Geological Survey’s campus in Reston, about 20 miles outside of Washington.

“Feels kind of strange,” said Kathleen Faison of Ashburn, a training specialist at the survey, as she headed into the office. “I kind of wish they would have kept us out until Monday.”

Faison said during the first few days of the shutdown, she followed the news closely, anticipating that she could be called back any day. But by week two, “I just kind of fell into my own personal routine,” she said.

She said she considered teleworking for the first day or two but eventually decided “I might as well just get back into the swing of things.”

Hydrologist Julian Wayland, carrying his lunch in a paper bag, said he wasn’t sure how much work had piled up during the shutdown. His primary job is determining the age of groundwater samples.

“We’re definitely behind,” he said. “I’m glad it’s over.”

Nationwide, the impasse had shuttered monuments and national parks. In Florida, the closure of the Everglades National Park had put almost all Florida Bay off limits, but commercial fishermen were set to return Friday. Parks across the country made similar plans.

The shutdown also mostly closed down NASA, the Environmental Protection Agency and the Interior Department. Critical functions of government went on as usual, but the closure and potential default weighed on the economy and spooked the financial markets.

Standard & Poor’s estimated the shutdown has taken $24 billion out of the economy.