City planning officials and business leaders noted that even with Lower Manhattan’s transformation into a 24-hour neighborhood, its residential density is still well below the average for the borough’s neighborhoods.

The Alliance for Downtown New York, which is funded by commercial property owners and runs a business improvement district in Lower Manhattan, pointed out that there are fewer workers today in the neighborhood — 235,000 in the private sector compared with about 270,000 before the Sept. 11 attacks — because there is 20-million square feet less office space (many units were not rebuilt after the attacks, while others were converted into residential apartments). In addition, the alliance said sections of the neighborhood remained fairly empty, especially at night, when daytime crowds of commuters and tourists leave.

“The key to continued progress is to tackle any thorny outgrowths of our success in a thoughtful and specific manner,” said Jessica Lappin, president of the alliance. “We should harness our momentum and build upon it constructively so businesses here can continue to thrive and enrich and enliven the entire community and all of New York.”

Some businesses said that at least some of the congestion on the streets had been caused by temporary construction projects, and would get better as those projects finished. Jordan Barowitz, a spokesman for the Durst Organization, which manages 1 World Trade Center, said many tenants now used an underground passage, which opened earlier this year, to reach the Fulton Center, a transit and retail hub. This has, in turn, reduced the crowding on Vesey Street.

City transportation officials have also taken steps to ease the crowding. They have extended the sidewalk at heavily used pedestrian crossings along Water and Whitehall Streets and built a new pedestrian and bike pathway along South Street on the waterfront, which is expected to draw pedestrians and cyclists away from congested interior streets.

Zoning regulations for Lower Manhattan have encouraged new developments to include public plazas and open spaces and locate subway stations inside buildings to improve pedestrian flow. The city’s Economic Development Corporation has also overseen a series of projects in Lower Manhattan, such as building a pedestrian bridge on West Thames Street and improving an esplanade along the East River, and plans to increase ferry service.