Yesterday I was Google surfing around South Dakota when I came upon
this bridge in Spearfish. As you can see, it's a mostly-normal AASHTO-style precast concrete bridge except that there's a nonstandard precast component about twenty feet long that rests on the center bent and supports the spans over the roadways. The center component has large haunches to support the roadway-span beams, but there are metal fittings, apparently with tie rods, that span every connection. I don't think the fittings were original equipment; perhaps they were retrofitted for seismic reasons. Per
http://bridgereports.com/1492794, it was built in 1971 and its condition is 7/9 in every category.
It's not at all clear why they would've done this, or, for that matter, done anything unusual here at all. The median is only sixty feet and the skew angle nil, so unusually long span lengths weren't required. I don't think aesthetics was a factor, either. I'm stumped.

By way of comparison, there are a few
like this in Hawaii. Here, though, the center component is cast in place integrally with the center bent, and the spans are unusually long.
There's also
a pair of similar bridges about six miles east of Spearfish, built at the same time. I didn't thoroughly scour the state looking for more, but I had a pretty good look around and didn't see any others.
Any idea why they would've built such a thing?
