If the airport feels a little more crowded this summer, it's not your imagination.

Airlines are expecting the busiest summer in the history of U.S. air travel, estimating that 246.1 million passengers will fly with U.S. airlines between June 1 and Aug. 31, 2018. That averages to about 2.68 million passengers per day during the period, according to the summer forecast issued Wednesday by the trade group Airlines for America (A4A).

The group pointed to a strong economy and "historically low airfares" for helping fuel what's expected to be a record summer for travel.

"As the economy grows along with household net worth, passengers are taking advantage of persistently low airfares for their summer travel plans," John Heimlich, A4A's Chief Economist, said in a statement.

The summer passenger numbers forecast by A4A would be a 3.7% increase from last the total last year, when a then-record 237.3 million travelers flew on U.S. airlines during the same period. Collectively, A4A says U.S. airlines have added 116,000 extra seats to their summer schedules in anticipation of the 2018 spike in passengers.

Elsewhere, A4A said average fares remained low heading into this summer.

"Through 2017, inflation-adjusted airfares continued to fall, averaging less than 2010 fares both with and without ancillary fees included," the group claimed in its statement. "In constant 2017 dollars, a round-trip 'all-in' ticket averaged $363 in 2017, well below the 2010 average of $380."

Looking just at the past few years, A4A said that if adjusted for annual inflation, the price of domestic air travel - including fees - had fallen by 12.5% since 2014.