PITTSBURGH -- More and more people are visiting the Flight 93 National Memorial in rural western Pennsylvania, authorities say, and new construction is scheduled to begin next year.

At the current pace, more than 1,000 bus groups will visit the park this year, almost double the number in 2011, said King Laughlin, vice president of the Flight 93 National Memorial Campaign. More than 200,000 people are expected to visit this year.

"It really seems to resonate with school groups and bus groups," Laughlin said Friday.

Park officials hope to break ground on a visitor center next spring, Laughlin said, as well as tree plantings and new walkways, all scheduled to be completed by 2014. A third phase, which could cost $5 million or more, will include a learning center and a tower at the entrance with 40 wind chimes. Price estimates for the whole project ranged from $67 million to $76 million.

Many improvements have been made since the park opened last year, including reforestation and other landscaping, said Patrick White, president of Families of Flight 93.

"It is coming forward like a painting. Each stroke of the brush brings it more to life," he said.

United Flight 93 was traveling from Newark, N.J., to San Francisco when it was hijacked by four terrorists. The 9/11 Commission said the terrorists likely wanted to crash the plane into the White House or the U.S. Capitol, but the jet went down in a field near Shanksville, Pa., after passengers fought back.

Both Vice President Joe Biden and Defense Secretary Leon Panetta plan to visit the memorial this week, according to the National Park Service.

Biden was scheduled to speak Tuesday, and the agency advised visitors to get there at least two hours before the 9:30 a.m. start because of security.

Panetta was to take a private tour of the memorial Monday.

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  • Flowers sit on a large boulder that marks the exact crash site in a field at the Flight 93 Memorial during the dedication ceremony, September 10, 2011 in Shanksville, Pennsylvania. The Flight 93 National Memorial was formally dedicated with former Presidents George W. Bush and Bill Clinton, Vice President Joe Biden, Secretary of the Interior Ken Salazar, Speaker of the House John Boehner and members of Congress in attendance. An estimated crowd of 5,000 watched as the memorial wall was unveiled with the names of the 40 passengers on the plane that crashed on September 11, 2001. (Photo by Jeff Swensen/Getty Images)

  • Flowers sit along the Wall of Names at the Flight 93 Memorial for the dedication ceremony, September 10, 2011 in Shanksville, Pennsylvania. (Photo by Jeff Swensen/Getty Images)

  • Mounted police officers patrols the field that will become the permanent Flight 93 memorial during a 9/11 Flight 93 commemoration September 11, 2010 in a field near Shanksville, Pennsylvania. (Photo by Archie Carpenter/Getty Images)

  • President Barack Obama and first lady Michelle Obama walk to the crash site of Flight 93 during their visit to the Flight 93 National Memorial Sunday, Sept., 11, 2011, in Shanksville, Pa., on the 10th anniversary of Sept. 11. (AP Photo/Pablo Martinez Monsivais)

  • First Sgt. Robert Baranik plays Taps following a ceremony to commemmorate the 10th anniversary of the Sept. 11, 2001 terrorist attacks, on a hill above phase 1 of the permanent Flight 93 National Memorial near the crash site of Flight 93 in Shanksville, Pa. Sunday Sept. 11, 2011. The crash site of United Flight 93 is marked by the large rock in the distance. (AP Photo/Amy Sancetta)

  • A memorial for Lorraine Grace Bay, a flight attendant on United Airlines, Flight 93, is seen as people gather before a candle light vigil at the Garden of Reflection Saturday, Sept. 10, 2011 in Yardley, Pa. (AP Photo/Alex Brandon)

  • Retired and active United Airlines flight attendants join hands at the Wall of Names at phase 1 of the Flight 93 National Memorial near the crash site of Flight 93 in Shanksville, Pa. Saturday, Sept. 10, 2011. (AP Photo/Gene J. Puskar)

  • Retired and active United Airlines flight attendants form a prayer circle at a gate along the Wall of Names at phase 1 of the Flight 93 National Memorial near the crash site of Flight 93 in Shanksville, Pa. Saturday Sept. 10, 2011. (AP Photo/Amy Sancetta)

  • Family and friends gather at the boulder that marks the site of the crash of Flight 93 on Sept. 11, 2001, in Shanksville, Pa. Saturday Sept. 10, 2011 following the dedication of phase 1 of the permanent Flight 93 National Memorial. (AP Photo/Gene J. Puskar)

  • Family and other visitors walk near a section of phase I of the permanent Flight 93 National Memorial, scheduled to be dedicated Saturday afternoon, near the crash site of United Flight 93 in Shanksville, Pa. Saturday Sept. 10, 2011. (AP Photo/Amy Sancetta)

  • The new Flight 93 National Memorial undergoes final preparations for Saturday's dedication ceremony on Sept. 8. 2011 in Shanksville, Pa.. (AP Photo/Gene J. Puskar)

  • A look at the United Flight 93 Memorial in Shanksville, Pennsylvania.