PHILADELPHIA — More Americans used buses, trains and subways in 2013 than in any year since 1956 as service improved, local economies grew and travelers increasingly sought alternatives to the automobile for trips within metropolitan areas, the American Public Transportation Association said in a report released on Monday.

The trade group said in its annual report that 10.65 billion passenger trips were taken on transit systems during the year, surpassing the post-1950s peak of 10.59 billion in 2008, when gas prices rose to $4 to $5 a gallon.

The ridership in 2013, when gas prices were lower than in 2008, undermines the conventional wisdom that transit use rises when those prices exceed a certain threshold, and suggests that other forces are bolstering enthusiasm for public transportation, said Michael Melaniphy, the president of the association.

“Now gas is averaging well under $4 a gallon, the economy is coming back and people are riding transit in record numbers,” Mr. Melaniphy said in an interview. “We’re seeing a fundamental shift in how people are moving about their communities.”