Photo taken by David Backlin in February 2011
BH Photo #193525
I think that placing a roof and sides over an otherwise plain structure is a nice way to dress it up. It also helps to keep large truck traffic off of the roadways and keep the neighborhood quiet and traffic levels down. I noticed from Photo #2 that modern steel stringers are supporting the roadway, and the sides are essentially fences that support the roof and provide a small amount of protection to traffic. It does not appear to be a truss of any kind, however.