Cars fill the highway, Nov. 22, in San Diego. November 24 marks the Thanksgiving holiday, one of the busiest travel days of the year. Gregory Bull/AP
Travelers check in for their flights at the United Airlines ticket counter at John Wayne Airport on Nov. 22, in Orange County, Calif. Mark Rightmire/The Orange County Register/AP
Travelers arrive as they greet their family at O'Hare International Airport in Chicago on Nov. 23. Nam Y. Huh/AP
Gov. Nathan Deal and wife Sandra greet US Marines, from left, Staff Sgt. Shawn Kallmeyer, Lance Cpl. Drew Greene, and Lance Cpl. Danielle Harrington, as banners reading 'Welcome Our Troops Home' are unveiled at Hartsfield-Jackson International Airport on Nov. 22 in Atlanta. David Goldman/AP
Ana Casares, of Miami, reads a magazine as she waits to check in her luggage at Miami International Airport in Miami, on Nov. 22. Casares is traveling with her family to visit her relatives in Quito, Ecuador, her family decided to travel early in the week to avoid the Thanksgiving travel crowds. Alan Diaz/AP
A train arrives as passengers wait to board at Amtrak's 30th Street Station on Nov. 23 in Philadelphia. Alex Brandon/AP
People line up to board the train to New York at Amtrak's 30th Street Station in front of artist Karl Bitter's Spirit of Transportation, created in 1895, on Nov. 23 in Philadelphia. Alex Brandon/AP
Travelers check their tickets with security at O'Hare International Airport in Chicago on Nov. 23. Nam Y. Huh/AP
Airline passengers go through security at George Bush Intercontinental Airport on Nov. 23, in Houston. David J. Phillip/AP
The Norton family gives Private Josh Norton a group hug after his return from a nine-month deployment in Iraq, for the Thanksgiving holiday, at Hartsfield-Jackson Atlanta International Airport in Atlanta, Georgia, Nov. 23. Tami Chappell/Reuters
The chief executive officers of both Lufthansa and Germanwings paid their respects at the plane crash site in France Wednesday.
ByLori Hinnant, Associated Press
Lufthansa's chief executive said Wednesday it will take "a long, long time" to understand what led to a deadly crash in the French Alps last week — but refused to say exactly what the airline knew about the mental health of the co-pilot suspected of deliberately destroying the plane.