This extension of Hanover's historic street grid will carry Cemetery Lane across the Dartmouth Cemetery.
It is hard to resist calling it a bridge "to Thayer School." If a Thayer parking deck ever goes in, visitors to campus will park there, and so this really will be a bridge "to the college." The Thayer end of the viaduct will be the gateway to the college:
One could even imagine a brick tower, or a towering gate, at that spot, serving as both an entranceway and a landmark:
Old Town bridge tower, Charles Bridge, Prague
Grove Street Cemetery gate, New Haven, Ct.
The Egyptian mode would be especially appropriate here, since the viaduct crosses a cemetery and Dartmouth has a sort of Egyptian thing going on (Sphinx, the Brace Commons pyramid, Amarna). The college motto would be a good thing to put above the gateway, because the visitor will be entering a wilderness of sorts, up in the trees.
Then this will be the new welcome for visitors after they come through the cemetery:
Not bad, but obviously a back entrance at the moment.
The footings will probably be minimalist, even spidery, to avoid landing in graves. (Incidentally, do they have a plan for what to do when they find unmarked graves?)
If the footings are bulked up and built of masonry, they could really announce themselves and interact with existing monuments (see this article on graves under the bridge at Montmartre in Paris for an idea). The bridge piers could even be rendered as obelisks and given plaques or inscriptions — as cenotaphs — although that would become hokey very quickly.
The deck should be wide enough for bicyclists and pedestrians to pass. There might be a need for rules about bikes.
The designers could do a nice elegant truss, not just a set of steel girders like Bartlett Hall's rear stair (Street View).
Could the school get a set of beautiful green trusses from a historic rail or highway bridge that is being replaced somewhere in the Northeast? The trusses could be placed end-to-end and the decks hung off the sides; this could be a little museum of engineering.
Or the viaduct could refer to the ski jump, built by the Boston Bridge Company: see this simple profile drawing, in a Rauner Blog post on the ski jump.
This does not seem like the place to use a state-park style boardwalk bridge. The site seems to demand something permanent and monumental in form if not in scale. It would be better to err on the side of the depressing than the cheerful.
[Update 08.06.2016: It turns out that Robert Fletcher, who singlehandedly brought Gen. Thayer's idea for a school into being (Lee Michaelides, "In the Beginning," Dartmouth Engineer Magazine), is buried in the Cemetery.]