NEW YORK (AP) — Adults who visit the Sept. 11 museum at the World Trade Center will be charged $24 admission.

The foundation board that oversees the lower Manhattan museum voted Thursday on the admission fee.

Families of Sept. 11 victims won't be charged. There will be discounts for children, seniors and schools.

The museum is scheduled to open this spring. It's still free to visit the memorial plaza with its twin reflecting pools.

Some relatives of Sept. 11 victims have criticized the decision to charge for the underground museum, which houses relics of the terror attacks.

Foundation officials say charging admission is necessary to cover the $60 million a year it'll cost to operate the site.

The museum has raised $700 million for construction costs but hasn't gotten government funds for operations.