LOS ANGELES — About 42.5 million Americans will travel more than 50 miles from home over the long Thanksgiving weekend, the first significant increase in holiday travel this year as the nation tries to shrug off the dampening mood of a poor economy.

In the East, the holiday rush got off to a bit of a messy start after motorists were snared and slowed by sticky goo from a leaky tanker truck that spilled driveway sealant along a 38-mile stretch of the Pennsylvania Turnpike.

The roadway was never completely shut down by the spill, Turnpike Commission spokesman Carl DeFebo said in a telephone interview, but traffic was slowed after the Tuesday night spill.

The worst-hit section of the turnpike was near Newcastle, about 10 miles from the Ohio border. Hundreds of cars were damaged as the goo worked its way up from wheels to engines, radiators and other parts of the cars, DeFebo said.

“There are no good options with the volume of vehicles during a busy holiday season,” he said, adding that the road had been largely cleaned up by Wednesday morning.

Rainy weather caused problems for air travelers in the East, with Newark, N.J., and Philadelphia airports reporting delays.

Thanksgiving is one of the busiest travel periods of the year as families make their way over rivers and through miles of woods to Grandma’s and other relatives’ houses for the traditional feast.

The 42.5 million Americans whom AAA projects will take to the roads and airways is up 4 percent from just a year ago. In 2008, the low point as the recession hit home, Thanksgiving travel was just 37.8 million people.

“Driving AAA’s projected increase in the number of Thanksgiving travelers is pent-up demand from Americans who may have forgone holiday travel the last three years,” said Bill Sutherland, vice president of AAA Travel Services.

“This is the first significant increase in any holiday travel this year,” Sutherland said in a statement. “Memorial Day travel was statistically flat while Independence Day and Labor Day travel experienced decreases of 2.5 percent and 2.4 percent, respectively.”