Retail sales are expected to rise 4.5 percent this year, a full percentage point more than the 3.4 percent growth in 2014, according to Kantar Retail, which excluded car dealers, gas and food service from its analysis.

Retail sales total $2.6 trillion annually and constitute a substantial portion of consumer spending, which accounts for 70 percent of the nation’s GDP.

After several years of spending gains driven by the wealthy, who snapped up personal aircraft and pleasure boats, the consumer economy “is in transition” as more lower- and middle-income households start to see financial improvements, said Ellen Zentner, senior U.S. economist with Morgan Stanley.

Online sales, though still 10 percent of total retail sales, are expected to grow 15 percent this year, same as in 2014, while sales at physical stores are expected to rise 3.6 percent, according to Kantar.

Much of the growth in retail, Kantar chief economist Frank Badillo said, will be driven by people under age 34, at both ends of the income scale, as that age group has seen the greatest employment gains.

Dollar stores, one of the fastest growing retail formats, are poised for a promising 2015. That’s thanks largely to falling gas prices, as their customers tend to be affected most by having a few more dollars in their pockets, said Ken Perkins, an analyst at Morningstar.

At the other end of the spectrum, the U.S. luxury market has been on stable footing for years, said Oliver Chen, a luxury analyst at Cowen and Co. “Wealthy people have always had money to spend,” Chen said.

Modest 1.6 percent sales growth last year at general merchandise retailers, which include Wal-Mart and Target, should accelerate in 2015 “as people who have been struggling to get by begin to struggle less,” said Michael Moriarty, a senior partner at A.T. Kearney.

A lot rides on the small urban formats that they’ve been rolling out, such as TargetExpress and Wal-Mart Express.

Department stores, where sales declined 2.1 percent in 2014, continue efforts to reinvent themselves to attract young shoppers, Moriarty said.

Despite positive holiday same-store sales increases at Macy’s Inc. (up 2.7 percent) and J.C. Penney (up 3.7 percent), both retailers announced plans to close stores this year

Nordstrom’s acquisition of Trunk Club, a Chicago-based e-commerce start-up that ships boxes of outfits for men to try on at home, may portend similar moves by retailers seeking to reach younger consumers.