Passengers at O’Hare International Airport in Chicago on Nov. 25, 2015. An airline trade group said that about 27.3 million Americans will fly over a 12-day period that starts Friday and ends the Tuesday after Thanksgiving, up 2.5 percent from last year. (Nam Y. Huh/AP)

A record number of ­Americans will kick-start the busy holiday travel season by hitting the road for Thanksgiving this year, the result of low gas prices and an improved U.S. economy, according to forecasts.

Nearly 49 million Americans are expected to travel at least 50 miles from home over the long weekend, the highest travel volume in nine years, according to estimates released Tuesday by AAA Mid-Atlantic. That’s about a million more than last Thanksgiving.

In the Washington region, more than a million residents are expected to travel over the holiday, and 9 in 10 will drive to their destinations, according to AAA. This holiday could be the biggest travel-by-car event since 2007.

“Expect additional delays on regional roadways and at area airports,” AAA spokesman John B. Townsend II said. “With so many Washingtonians traveling for Thanksgiving, try to avoid traveling through major cities during peak travel times.”

The main concern for the Washington region will be traffic congestion, as more than a million of the estimated 1.2 million area residents traveling next week will make their exit by car. About 88,500 people are expected to fly, and 26,400 will go by bus, train or boat, AAA said.

If historical traffic patterns serve as a guide, the exodus is expected to start early next week, with Tuesday afternoon probably the worst time to be on the road, according to an analysis of Thanksgiving travel by the region’s Transportation Planning Board.

The analysis from previous years found that travel speeds on area roads dropped well below average during the three days leading to Thanksgiving, but Tuesday was by far the worst. Speeds could drop below 20 mph in areas of the region’s road network where during a typical commute the average speeds generally don’t drop below 40 mph.

“The best times to leave will be in the mornings, because the roads should be less crowded and you will have more time to get to your destination safely. If your schedule permits, traveling on the holiday itself often results in less congestion and fewer crowds,” Townsend said.

Transportation officials and experts say residents should expect freeways, airports and the platforms at Union Station to be extra crowded. Travelers should also be prepared to navigate long lines at airports and rail terminals, and tight security is expected.

Despite recent increases in the price of gas, many who are driving may be lured by prices among the lowest in the past decade. Nationally, the average price is $2.17 a gallon, 12 cents above the average for Thanksgiving Day a year ago. The average price in the Washington region Monday was $2.18 a gallon, 2 cents more than 2015’s average, according to AAA.

Another factor boosting travel is growing confidence in the U.S. economy in recent months, ­including rising incomes for ­middle-class and poor Americans and increased consumer spending, AAA says.

Transportation officials say planning is key, as is giving yourself plenty of time and patience. Be aware of your surroundings, don’t leave your bags unattended and report any suspicious activity or unattended items.

For those people who will be driving, alternative routes may not necessarily guarantee a quicker trip, but experts recommend going during off-peak hours, early in the morning or late at night to avoid the biggest backups. Make sure your vehicle is ready for the road by scheduling a professional checkup and ensuring that your vehicle’s batteries and tires are in good condition before leaving home. Also, keep an emergency safety kit in your trunk.

In Virginia, the heaviest holiday traffic typically occurs after 11 a.m. Wednesday and from 10 a.m. to 10 p.m. Sunday. In Maryland, transportation officials say the best travel times are before 6 a.m. and after 11 p.m. Tuesday and Wednesday and before 9 a.m. and after 9 p.m. Thursday through Sunday.

For air travelers, the Friday, Tuesday and Wednesday before Thanksgiving and the Sunday and Monday after the holiday are traditionally the busiest at area airports. The Metropolitan Washington Airports Authority says travelers should expect full flights, full luggage bins aboard airplanes and more gridlock near airports.

If flying out of town, book parking in advance. If picking up someone, wait at the cellphone lot or park and greet visitors at the airport and avoid adding to the traffic congestion around the airport.

“Build enough time into your journey to navigate through check-in and security, and to stop for a bite to eat or buy a gift,” MWAA spokesman Rob Yingling said. For future holidays, he said, travelers should consider enrolling in the Transportation Security Administration’s PreCheck program or U.S. Customs and Border Protection’s Global Entry program to take advantage of expedited screening at participating airports.

The TSA says air travelers should expect more lines Thanksgiving week,the year’s top holiday for travel. Many TSA officers will be working overtime to help handle the large numbers of travelers, an agency spokeswoman said.

On the rails, the Tuesday and Wednesday before Thanksgiving and the Sunday after the holiday promise to be the busiest. Rail passengers should carry photo identification at all times, Amtrak said, because it may be requested aboard trains.

Amtrak is adding trains and seats on several routes across the country. In the Northeast Corridor, the Acela Express and Northeast Regional services will run full and extended schedules with more trains to expand capacity between Washington and Boston, Amtrak said.

And, just in time for the holidays, Amtrak recently upgraded WiFi on its Acela trains to make connectivity six times faster, part of upgrades to passenger service in the Northeast Corridor.

Wick Moorman, president and chief executive of Amtrak, said in a statement that Amtrak employees are preparing to boost the service during Thanksgiving week, the busiest period for rail travel. Last year, more than 751,000 people traveled on Amtrak during the holiday. The same demand is expected this year, the railroad said.

“We continue to focus on providing innovative and convenient travel options for our customers, and the Thanksgiving travel period is a great opportunity to put our best foot forward,” he said.