A real bridge was tested in 1973 to see how it responds to a truck driving on it. The bridge had steel boxes and a concrete slab, and was designed for two lanes. The researchers measured how the bridge moved and bent when the truck was on it. They compared this real data to computer predictions and found they were pretty close. They also looked at how the bridge reacted when the truck hit it, and calculated how much extra force the impact added. The researchers checked if the bridge behaved as expected based on its design.