Just as delighted is New York’s governor, Andrew M. Cuomo, who set the bridge project in motion after more than a decade of official vacillation over whether money should be spent on repairs or replacement. In an interview, he said he saw the state’s long indecision as a “metaphor for government incompetence and unfulfilled promises,” while the opening of the Tappan Zee’s replacement was a sign that government can still build things.

“It’s a physical manifestation of New York’s spirit of possibility,” he said.

Mr. Cuomo is considered a possible presidential candidate in 2020 and would presumably use his record of building infrastructure — he oversaw the opening of the first phase of the Second Avenue subway, has started overhauls of La Guardia Airport and Pennsylvania Station and unveiled an ambitious renovation plan for Kennedy Airport — as a highlight of his résumé.

Ms. Barbas took me in an S.U.V. from the bridge’s Tarrytown entrance across the 2,230-foot main span onto the water-hugging approach to Rockland County, stopping long before reaching the shore only because workers had blocked off a section to erect a sign gantry. Despite the forklifts, construction trailers, portable toilets, tool chests and piles of steel and rubber parts strewn about and the scattering of many of the 900 hard-hatted, Day-Glo-vested workers putting down the finishing touches, the new bridge was a breathtaking sight.

The eight towers that slope outward like welcoming arms and anchor both bridges to the riverbed are largely completed, soaring the height of 40-story buildings over the river’s gunmetal waters. In the background, as if meant for a traveler’s postcard, lie the end of the emerald-green Palisades bluffs and the houses of Nyack and South Nyack.