Why do bridge designs account for the Earth's curvature?

The design of long bridges, like the Verrazano–Narrows Bridge in New York and the Humber Bridge in England, must take into account the Earth's curvature. In the case of the Verrazano, its two towers are 1 5⁄8 inches farther apart at their tops than at their bases, and in the Humber's case, the difference is 1.3 inches. (And no, I have not measured them myself.)  How do flat earthers explain this?

a) When the massive round earth conspiracy hears about the plans for a new long bridge, the tell the bridge designers to tell everyone that the towers are not parallel, even though they actually are.  The designers are threatened with death if they tell the truth about the bridge design.

b) Other. Please elaborate.

This has already been discussed at some length HERE.

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The linear accelerator in the SLAC National Accelerator Laboratory is 2 miles long and it needs to be actually straight and not follow the curvature of the earth, otherwise the electrons will hit into the walls and the whole thing won't work. The curvature of the Earth is something like "8 inches a mile". Therefore the center of the accelerator is in fact closer to the Earth's center than the edges by about 8 inches.

This is also true for J-PARC (Japan Proton Accelerator Complex). Here's some documents on how curvature does matter while building that facility:

http://www.slac.stanford.edu/econf/C06092511/presents/TU004_PPT.PDF
http://www.slac.stanford.edu/econf/C04100411/papers/010.PDF