The National Museum of African American History and Culture, pictured on opening day, has adjusted its approach to timed passes. (Marvin Joseph/The Washington Post)

Starting Dec. 19, the National Museum of African American History and Culture will make free, same-day passes available online rather than requiring visitors to line up in person. The museum is also allowing a limited number of walk-up visitors after 1 p.m. on weekdays, crowds permitting.

The museum announced that advance timed passes for April will be distributed online and by phone beginning Jan. 4, while passes for May will be available starting Feb. 1. The passes are available by visiting nmaahc.si.edu or calling 866-297-4020.

Passes obtained online may be printed or displayed on smartphones.

The changes to the visitor policies come after some 600,000 guests have visited the museum since it opened Sept. 24.

(McKenna Ewen/National Museum of African American History and Culture)

Although the timed passes have successfully controlled crowds and wait times, they have not been fully used during the week, said Beverly Morgan-Welch, the museum’s associate director for external affairs.

About 40 percent of advance passes are being used on weekdays, and 60 percent on weekends. Officials say they wouldn’t want 100 percent usage, since early estimates for how many visitors could be accommodated were too high and did not predict the long length of stays.

Weekday attendance averages about 6,300, while weekends are closer to 8,500, according to the museum.

Perhaps the most important change is for group admissions. Starting Dec. 19, noncommercial groups of 10 or more guests can request passes up to a year in advance directly through the museum’s website.

The museum hopes the new policies will decrease the perception that there’s a scarcity of passes. Morgan-Welch said that in the frenzy to get passes, guests grabbed multiple passes for multiple days before knowing if they could actually use them. Distributing one month of free passes, rather than the three-month blocks used in August and October, should reduce the public’s impulse to grab more passes than needed.

Colder weather prompted the museum to shift the in-person line for same-day tickets to a virtual queue, Morgan-Welch said. Beginning next week, same-day passes will no longer be distributed outside the museum at 9:15 a.m. Instead, visitors may obtain passes for that day from the museum’s website, starting at 6:30 a.m. Only a limited number of same-day passes, and no walk-up passes, will be available on weekends, because more pass holders use their tickets on Saturdays and Sundays, she said.

From Dec. 26 through Dec. 30, the museum will offer extended hours to accommodate the expected high demand of the holiday season.

For those five days, the museum will be open from 10 a.m. to 7:30 p.m.