Eighteen months after its triumphant opening, the popular National Museum of African American History and Culture is testing a new admission policy: No timed passes will be required for four Wednesdays next month.

“Walk-Up Wednesdays” will allow museum officials to test a no-pass-required entry to the Smithsonian museum, which opened Sept. 24, 2016, and has welcomed more than 3.3 million visitors since.

On April 4, 11, 18 and 25, visitors can enter without passes, officials announced. The museum distributed timed passes for all of April — including these four days — and it will give visitors holding passes priority. Everyone else will be allowed in subject to capacity.

The museum will not distribute same-day passes online — as it does daily starting at 6:30 a.m. — as it tests its no-pass policy.

“Walk-Up Wednesdays in April will help us to determine how to manage visitor demand,” museum director Lonnie G. Bunch III said in a statement. “We don’t want to disappoint our visitors by reaching capacity and having them wait in long lines for space to become available inside the galleries. The goal of this pilot program is to provide greater access for the public while maintaining the safety and security of our visitors.”

Since it opened, the museum has issued advance timed passes to control crowds and prevent long lines at its entrances. On the first Wednesday of every month, it has released thousands of free passes on a first-come basis through its website, nmaahc.si.edu. The museum will distribute passes for July on April 4 beginning at 9 a.m.

The system has crashed repeatedly since it was introduced in 2016. Only last month it experienced “technical difficulties” that lasted more than an hour and left patrons thinking that passes for June were gone.

In addition to advance tickets, the museum distributes same-day passes on its website every morning. A limited number of walk-up passes are available weekdays after 1 p.m. at the Madison Drive side of the building. No walk-up passes are available on Saturdays or Sundays because of the high volume of visitors.

Groups are still required to have timed passes, according to the museum’s website.