Several family members of the 40 passengers and crew who died on hijacked United Airlines Flight 93 say they're fed up with controversies surrounding the design of a national memorial.

The families of four victims held a news conference in Pittsburgh. They say it's time to get on with developing the memorial near Shanksville, where the hijacked airliner crashed during the Sept. 11 terrorist attacks.

The plane was the only one of four hijacked that day that terrorists were unable to crash into a building. A government inquiry determined the plane crashed as the passengers attempted to wrest control from the four hijackers.

The planned memorial has been dogged by some critics who say its crescent-shaped design and other features call to mind Islam or subtly include the hijackers alongside the passengers and crew.