Travelers line up to board a train in Philadelphia during the busy Thanksgiving travel period, 21 Nov 2007

Millions of Americans are on the roads or at the airports Wednesday, traveling to be with family and friends for Thursday's Thanksgiving holiday.

This year is expected to mark the largest Thanksgiving travel period ever - despite rising gas prices and fears of air delays.

The American Automobile Association estimates a record 38.7 million Americans will travel at least 80 kilometers for Thanksgiving, compared with the prior record of 38.1 million during last year's holiday travel period.

Most of the travelers are likely to go by car, while the rest will fly or take trains or buses. Thanksgiving is traditionally the busiest travel day of the year in the United States.

President Bush issued a holiday proclamation, saying Thanksgiving is a time for Americans to gather in a spirit of gratitude with family, friends and neighbors. He said Thanksgiving is also a chance to serve others and to share blessings with those in need.

Thanksgiving is a North American holiday to give thanks at the end of the harvest season, with family gatherings and holiday meals that include turkey, stuffing and pumpkin pie. It is celebrated on the fourth Thursday of November in the United States and on the second Monday of October in Canada.

The earliest Thanksgiving events were held in former British colonies in what are now U.S. states - in present-day Virginia in 1619 and present-day Massachusetts in 1621.

Some information for this report was provided by AP.