The 35W bridge collapse is bringing renewed attention to the country's aging roads and bridges. Investigators will consider many factors as they determine why the bridge came down. One of those is the increased traffic over the bridge in the past 40 years. During that time there's been a dramatic increase in the number of trucks on the road and those trucks are heavier. Experts say that combination can significantly reduce the life of roads and bridges. Minnesota Public Radio's Dan Gunderson explains.