More people are expected to make trips this Thanksgiving season amid heightened security due to terror threats during the busy travel period.

In the Philadelphia region, AAA Mid-Atlantic estimates that more than 542,000 people in the city and its Pennsylvania suburbs will travel at least 50 miles for the holiday this year, a 1.4 percent increase from 2014 and the most travelers since 2007.

Nearly 89 percent of those visiting family and friends out of town will go by car, and about 8.5 percent plan to travel by air, the travel group says.

The busy travel period comes as the State Department has issued a global travel alert, warning U.S. citizens of "increased terrorist threats" from groups like the Islamic State, al-Qaeda and Boko Haram.

"Exercise particular caution during the holiday season and at holiday festivals or events," the alert says.

Secretary of Homeland Security Jeh Johnson said over the weekend that the agency knows "of no credible and specific intelligence indicating a Paris-like plot on the U.S. homeland" as the holiday season approaches, but homeland security and law enforcement officials were "working overtime" to monitor threats and evaluate security measures.

The busiest travel days on the roads and at airports will be Wednesday - the day before Thanksgiving - and Sunday, according to AAA, while Amtrak says Tuesday, Wednesday and Sunday are expected to see the most train riders.

Those traveling by car will enjoy some of the lowest Thanksgiving gas prices since 2008.

In Philadelphia and the surrounding Pennsylvania counties, prices were averaging $2.31 per gallon Tuesday, down from $2.96 a year ago. In the city's New Jersey suburbs, fuel averages $1.90 per gallon, down from $2.68 at this time last year.

Philadelphia International Airport suggests travelers arrive at least two hours before their flights in case extra time is needed to check in and get through security.

The airport was also reminding passengers that US Airways has merged with American Airlines, now the dominant carrier in Philadelphia. All US Airways signage at airport has been replaced with American branding.

Airport travelers can also take advantage of the recently opened secure corridor that lets passengers walk to and from Terminal F without needing to go through security a second time.