Mr. Robins directed the protracted public-private effort to create the New Jersey system from 1988 through 1994. He noted that those residing in the tens of thousands of new units within walking distance of light-rail stops  and others due to open at Liberty Harbor North and Gull’s Cove in Jersey City  now have an easier alternative than driving for getting to work, going shopping or taking in a show.

The Jersey City planner Robert Cotter, one of many local officials, planners and light-rail riders who contributed to the study, told the researchers that he was increasingly seeing vacant spaces in parking areas set aside for employees at office buildings in his city.

Yet Mr. Robins  like Jamie Lefrak, a principal of the Lefrak Group, builder of the Newport residential/office/retail complex  expressed amazement that the light rail was ever built. “We established a route through what were essentially fallow areas,” he said, using a more genteel term for stretches that Mr. Lefrak described as “places most people would not want to go.”

The light-rail passage in turn attracted developers to rehabilitate those places, while providing new mobility for the large, mostly immigrant, community already established in Union City, which has relatively few car owners.

Census figures rank Union City, perched atop the Palisades, above Hoboken, as the most densely populated city in the country.

“When the station was built at Bergenline Avenue,” Mr. Robins said, “it was very meaningful for the people there. Not only was the commute time to jobs in New York and New Jersey chopped by as much as 75 percent, but they suddenly had a convenient way to get to the shopping mall at Newport.”

He called Union City’s turnaround one of the most heartening results of his work on the creation of the system.