Drivers should be prepared for busy roads this Fourth of July weekend as the number of holiday travelers is expected to reach an all-time high.

More than 615,000 vehicles are expected to travel on the Maine Turnpike from Friday through Saturday, likely the busiest days of the weekend, the Maine Turnpike Authority said.

Weekend traffic is expected to be 1.25 percent higher than last year, setting a new record for the highway. Overall traffic grew by 2.4 percent in the first five months of the year, compared to the same period in 2016, the busiest year on record for the turnpike. Traffic was expected to be heaviest northbound Friday afternoon and evening, and Saturday morning and afternoon.

That mirrors anticipated traffic nationwide, which is projected to be heavy. Almost 2.3 million New Englanders will travel during the five-day period from Friday to Tuesday, and the vast majority will be driving, according to AAA Northern New England.

That is a 3 percent increase from the year before, and the 16th straight year of rising auto travel, AAA said.

“This Independence Day will be historic,” said Dan Goodman, manager of public affairs for AAA Northern New England. “Traveler numbers are up and gas prices are down, adding to what has already been a busy summer travel season.”

Nationwide, AAA expects about 44.2 million Americans to travel for the long weekend, the most on record. Roughly 85 percent will drive.

Goodman attributed the expected record travel to low unemployment, a strong economy, low gas prices and high consumer confidence. Gas prices over the Fourth of July weekend will be the lowest since 2005, according to Gasbuddy.com, with a national average of $2.21 per gallon. Maine’s average gas price is $2.25, about 5 cents lower than last year, AAA said.

Flight travel in New England over the weekend is expected to grow almost 6 percent, but the number of passengers coming into the Portland International Jetport will likely remain flat, Assistant Airport Director Zach Sundquist said.

“We are expecting about 36,000 passengers. That’s a pretty standard Saturday to Wednesday for the summer here in Portland,” he said.

Rail travel also is expected to be busy, with tickets for some Downeaster trains between Boston, Portland and Brunswick already sold out.

“Typically it is a very busy weekend. We already have a couple trains sold out for Friday and another one sold out for Saturday,” said Patricia Quinn, head of the Northern New England Passenger Rail Authority, the agency that runs the Downeaster service.

Weather could affect travel over the weekend, with rain expected between Friday evening and Sunday morning, some of it heavy at times, prompting the National Weather Service to issue flood and severe thunderstorm watches for parts of the state. While Saturday morning is expected to be clear, the rain will move in Saturday afternoon or evening and continue into early Sunday. By Sunday afternoon, the rain will have moved on, and the rest of the holiday weekend is expected to be clear and sunny.

Maine’s ports also will be busy, with large cruise ships due in Portland and Bar Harbor. The Grandeur of the Seas, a Royal Caribbean International ship, is scheduled to sail into Portland on Sunday with 2,700 passengers and crew before heading to Bar Harbor on Monday. The Summit, a ship with more than 3,000 passengers and crew, is scheduled to dock in Portland on Monday.

The number of tourists bound for Maine has grown for the last four years, and many people visit during the summer to enjoy the state’s beaches, lakes, mountains and seafood. Almost 36 million tourists came to Maine in 2016.

Cool, rainy weather has made for a slow start to the state’s tourist season, but looking ahead it appears that 2017 is going to be another strong year for the tourism industry, said Chris Fogg, CEO of the Maine Tourism Association.

“Bookings for the weekend are really strong and moving forward look really good,” Fogg said. “Along with Memorial Day, Fourth of July is one of the biggest weekends of the year.”

Peter McGuire can be reached at 791-6325 or at:

pmcguire@pressherald.com

Twitter: @PeteL_McGuire