The Maine Turnpike Authority is predicting a 3.1 percent increase in Labor Day weekend traffic over last year’s holiday travel as good weather and low gas prices continue to propel what’s already been a robust summer tourism season.

“The weather is supposed to be very good and warm, gas prices are low and the traffic trends have all been very positive,” said Doug Davidson, chief financial officer for the authority.

The turnpike expects to make more than 1 million transactions between Friday and Monday, the vast majority being passenger cars passing through its tollbooths. Eight million motorists were counted on the turnpike for the entire month of August.

Friday is expected to be the busiest day with more than 324,000 vehicles and heavier traffic heading northbound in the afternoon.

The strong summer tourism season is extending a year of high volumes of traffic. From January to July, the turnpike experienced a 4.7 percent increase in traffic compared to the same period in 2014.

Davidson said the predicted 3.1 percent increase is a “conservative” estimate, given how strong the volume of traffic has been this year. He won’t be able to check the prediction against actual Labor Day weekend totals until Sept. 8.

Nationally, the American Automobile Association estimated that 35.5 million Americans would travel 50 miles or more over Labor Day weekend, which would make it the busiest Labor Day on American roads since 2008.