A record number of Americans are estimated to hit the roads for the Fourth of July. Here are the places and times it will be the worst.

Elaine Thompson/AP

• A record number of Americans are estimated to hit the roads for Fourth of July.
• Low gas prices and a booming economy mean families have plenty of disposable income to invest in summer travel, AAA says.
• The group, along with the analytics firm INRIX, has calculated the most crowded places and times.
• Here's where traffic will be worst - and the best time to leave to avoid it.

Wednesday, on the eve of the July 4 holiday, is set to be one of the busiest travel days of the year.

AAA estimates that nearly 49 million Americans will hit the road to celebrate the Independence Day holiday, a 4.1% increase over last year's travel volumes and a new annual record.

"In addition to lower gas prices compared with last summer, broader economic fundamentals remain strong," the group said in a press release. "Low unemployment, robust consumer spending, and rising disposable incomes are all encouraging more consumers to invest their hard-earned money in travel this summer."

Travelers won't just be clogging up highways from coast to coast, they'll also be heading to airports in a similarly record-breaking fashion, with 3.96 million people expected to fly and another 3.55 million expected on trains, buses, and cruise ships.

But while gas is cheap, holiday-makers will be paying more for airfare, which is up about 10%, AAA estimates.

In collaboration with the analytics firm INRIX, AAA has predicted where traffic will be the worst, and when you can leave in order to avoid it.

"With record-level travelers hitting the road this holiday, drivers must be prepared for delays around our major metros," Trevor Reed, transportation analyst at INRIX, said in a press release. "Although travel times are expected to nominally increase throughout the week, hands down, Wednesday afternoon will be the worst time to be on the road."

Here are the cities with the most anticipated congestion, and which times to avoid: