I'll tell you why, that bridge is at the lowest part of two hills, there is also a depression that's wider that the width of the bridge, too. As that truck goes under the bridge the rear tandems go into that depression this making the front of the trailer clear the bridge until those tandems get out of that and start climbing up the incline just passed the bridge, and therefore making the middle of the van hit the bridge because the trailer's axels are still descending and haven't reach that depression under the bridge. If he kept going the rear of the trailer would clear (that also depends how far forward the trailer axels where put) and when he (Theoretically) got on the other side of the bridge only the middle part of the trailer would have been damaged! Understand? :)
