It’s been 20 years since disability advocates won the fight to have the Franklin Delano Roosevelt Memorial in Washington, D.C. depict the former president in a wheelchair at the site. But they say there is more work to do to make the space fully accessible to all people with disabilities and serve as the “monument to freedom” that former President Bill Clinton said it would be upon the statue’s dedication.

Sen. Tammy Duckworth on Tuesday will introduce a resolution with D.C. Delegate Eleanor Holmes Norton calling on the National Park Service to improve the memorial’s accessibility to blind and low-vision visitors and to create accessible education materials about the site’s history.

While the 7.5-acre memorial was designed in the 1970s with wide stone paths and open spaces to be accessible to a broad range of people, its signs, placards and murals are still not accessible to people with limited vision. In fact, the braille on the monument is almost completely unreadable—and has remained that way since the sculptures were installed in 1997.

The braille on the memorial is too oversized for any person to read it, and some of it is too high for any human to reach. Sculptor Robert Graham told the Washington Post in 1997 that the braille was “a kind of invitation to touch, more than anything” and was not meant to be read. However, Park Service rangers and Sen. Daniel Inouye, who co-chaired the FDR Memorial Commission, appeared to believe the opposite, saying it would be legible. Shortly after its unveiling in 1997, Rep. David Bonior of Michigan introduced a resolution calling for the “artistic” braille to be supplemented with readable braille, but the issue remains today.

“Our national parks should be accessible to everyone, whether they read Braille or printed text, whether they get around by walking or in a wheelchair, like the American President whom this site honors,” Duckworth, who lost both legs serving in the Iraq War and often uses a wheelchair, said in a statement on Tuesday. “That’s why I’m proud to introduce this important resolution with Congresswoman Holmes Norton that honors the work of disability advocates in securing this statue and makes clear that there is much more work to be done to make this historic site accessible to all Americans.”