KAPOLEI, Hawaii — From the start — when Honolulu officials began talking about building a 20-mile elevated train line near the southern coast of Oahu — there were concerns. How much would it cost? What would it do to the character of a state that has long celebrated its natural beauty and isolation? Can an island in the middle of the Pacific Ocean handle the kind of ambitious public works project one would associate with urban centers like Boston and New York?

Eight years after voters in Hawaii approved a referendum clearing the way for construction of the rail line, many of the concerns that have been voiced during a 40-year debate over the project have turned out to have merit.

The project was initially projected to cost $4.6 billion, but that number now is $6.7 billion, forcing the city in January to approve a five-year extension of a general excise tax surcharge to help cover the overrun.

City officials are awaiting the opening of two sets of bids, covering the final 10 miles of the project, to see if even that is enough. At this rate, city officials said, it could have the distinction of being, on a per-capita basis, the most expensive transit project in the country’s history — in a state that also has the highest per capita cost of living in the nation.