Audiences hit the road with Robin Williams as his family-vacation romp "RV" opened at No. 1 with $16.4 million, while the acclaimed Sept. 11 drama "United 93" debuted with $11.6 million.

Studio estimates Sunday had Universal Pictures' "United 93" in second place, just ahead of Disney's sports comedy "Stick It," which premiered with $11.3 million. Those rankings could change once final numbers are released Monday.

The weekend's other new wide release, Lionsgate's spelling-bee drama "Akeelah and the Bee," was No. 8 with $6.25 million.

The 20th Century Fox release "RV" was expected to debut on top, but "United 93" had been an unknown quantity, with Hollywood analysts wondering whether movie-goers were ready to relive the horrors of the Sept. 11, 2001, terrorist attacks.

"It's not about the positioning of the film. It's about the fact that the American public spoke out," said Nikki Rocco, head of distribution for Universal Pictures. "This is a wonderful result. What they said was that it wasn't too soon for a film about Sept. 11."

Married couples accounted for just over half the "United 93" audience, and 71 percent of viewers were 30 and older, according to Universal.

With painstaking authenticity, "United 93" recounts the horrific end of passengers who fought back against their hijackers aboard one of the commandeered planes, which crashed in rural Pennsylvania.

Families of those killed aboard Flight 93 cooperated with director Paul Greengrass ("The Bourne Supremacy," "Bloody Sunday"), who re-creates the experiences of passengers and air-traffic controllers in a documentary-style drama. "United 93" earned widespread praise from critics.

Shot on a modest budget of $15 million, "United 93" should easily turn a profit once theatrical, television and DVD revenues are tallied. Universal said it will donate 10 percent of the first weekend's grosses to the Flight 93 National Memorial in Pennsylvania.

Playing in 1,795 theaters, about half as many as "RV," "United 93" averaged a solid $6,462 a cinema, the best results among the top-10 movies.

"We can now kind of put to bed any idea that people are not ready to see this type of movie. The numbers speak for themselves," said Paul Dergarabedian, president of box-office tracker Exhibitor Relations.

Coming this August is Hollywood's second Sept. 11 dramatization, Oliver Stone's "World Trade Center," starring Nicolas Cage in the story of two Port Authority policemen trapped in the rubble of the twin towers.

"RV," starring Williams as a dad taking his family on a slapstick-filled vacation, debuted in 3,639 theaters and averaged $4,507. The gymnastics tale "Stick It," starring Missy Peregrym and Jeff Bridges, averaged $5,523 in 2,038 theaters.

Overall business rose for the sixth-straight weekend, with the top-12 movies taking in $90.7 million, up 12 percent from the same weekend last year. After a big slump in 2005, attendance is running 4 percent ahead of last year's, with Tom Cruise's "Mission: Impossible III" opening Friday and kicking off what is expected to be a huge summer at the movies.

Estimated ticket sales for Friday through Sunday at U.S. and Canadian theaters, according to Exhibitor Relations Co. Inc. Final figures will be released Monday.

1. "RV," $16.4 million.

2. "United 93," $11.6 million.

3. "Stick It," $11.3 million.

4. "Silent Hill," $9.3 million.

5. "Scary Movie 4," $7.8 million.

6. "The Sentinel," $7.6 million.

7. "Ice Age: The Meltdown," $7.05 million.

8. "Akeelah and the Bee," $6.25 million.

9. "The Wild," $4.7 million.

10. "The Benchwarmers," $4.4 million.