Robert Hammond, co-founder and executive director of the charity that turned an abandoned elevated railway into New York’s innovative High Line park, said Monday that he will leave the organization by the end of the year, reports The New York Times.

Mr. Hammond and Joshua David started Friends of the High Line in 1999, overseeing the transformation of the train line into a green space above Manhattan’s streets that attracted 4.4 million visitors last year. The model is being emulated in other cities in the United States and Europe, and Friends of the High Line has raised more than $80-million to fund construction of the park’s third and final section.

“I always had three goals for the High Line: that it’s a well-loved park, that it inspires others to start their own projects, and that it not be dependent on Josh and me,” said Mr. Hammond, who previously developed start-up companies. “It’s a good time to transition. I’m an entrepreneur at heart. My gut has been telling me that it’s time to start something new.”