What is the design I can use for the strongest bridge under this criteria?

Now for a project I have to build a bridge with popsicle sticks and the max number sticks I can use is 40. The bridge has to span over a 6 inch river and a 2 inch tall boat has to be able to pass under it. We are only allowed to used popsicle sticks provided for us already and white Elmer's glue. The record weight that a bridge held a few years back was 280 pounds. What should my design include so I can at least make a bridge that can hold 70 pounds at least?