As the city’s economy soared and its population grew from 2003 through 2007, something unusual was happening on the streets and in the subway tunnels.

All those tens of thousands of new jobs and residents meant that more people were moving around the city, going to work, going shopping, visiting friends. And yet, according to a new city study, the volume of traffic on the streets and highways remained largely unchanged, in fact declining slightly. Instead, virtually the entire increase in New Yorkers’ means of transportation during those robust years occurred in mass transit, with a surge in subway, bus and commuter rail riders.

“What you see is that for the first time since at least World War II, all of the growth in travel in the city has been absorbed by non-auto modes, primarily by mass transit,” said Bruce Schaller, New York’s deputy transportation commissioner for planning and sustainability, who wrote the study, which is to be released on Monday.

“Now we’ve really turned a corner in the city in that all of the growth in travel over the last four years has been absorbed by mass transit and so, in terms of the city’s sustainability goals, this is very encouraging to see.”