Zee new span’s opening on Fri.

FASTEN your seat belts.

The $4 billion span replacing the Tappan Zee Bridge is set to start carrying commuters across the Hudson River on Friday.

One span of the future Gov. Mario M. Cuomo Bridge will open to westbound traffic. The new span signals near-completion of a project to replace the 62-year-old Tappan Zee, which has served as the poster child for America’s crumbling infrastructure. The second span is scheduled for completion in the spring.

The 3-mile-long bridge linking Westchester County to Rockland County and the New York State Thruway across the widest point in the Hudson is one of the largest public infrastructure projects underway in the U.S., and a model of the latest engineering. It will take more than 50 million vehicles a year across the river.