The U.S. is expanding ski-resort-style security checkpoints to six more airports, after tests in two cities showed the approach speeds passengers through lines.

The system lets people select "beginner" or "expert" lanes, reducing wait times 35 percent for business travelers in Salt Lake City, said Earl Morris, the airport's security director. The effort, also under way in Denver, is called "Black Diamond" for symbols that mark the toughest ski slopes.

The Transportation Security Administration hasn't yet named the six airports where the program will be in place by the end of April. The agency, which took over passenger screening responsibilities at the nation's 2,500 airport security lanes after the Sept. 11 attacks, is trying to reduce long lines and complaints about delays.

The security agency will pick the six new airports for the program based on factors such as the space available at checkpoints and support from airlines and airports, said Christopher White, a TSA spokesman.

"A number of airports are interested," said Debby McElroy, an executive vice president at the Airports Council International-North America trade group. "We need to find ways to make the passenger screening system more efficient."