Looking Northeast, South Side Of Plate Girder Bridge Which Carried The Interurban Line Across The Fox River. Note The Steel-Frame Supports For The Catenary.
Photo taken by Historic American Engineering Record
View photos at Library of Congress
BH Photo #117969
They didn't, based on period maps that show the interurban crossing the river at Main Street in Ottawa.
1929 Map:
http://www.historicmapworks.com/Map/US/47753/Ottawa+and+Sout...
1906 Map:
http://www.historicmapworks.com/Map/US/62659/Ottawa+and+Sout...
How did they manage to use the bridge as an electric rail and as a towpath at the same time?
To correct a comment left in 2009, the stone support are the remains of the Superior Street Bridge:
Those are not "Steel-Frame Supports For The Catenary", they are fairly new and have square lights on them. They are not even over the railroad portion of the bridge, they are over the aqueduct. The only thing left of the railroad bridge are the stone piers in the foreground.
This is actually part of the Illinois & Michigan canal aqueduct over the Fox River. The Illinois Traction System was abandoned in the 1930s, around the same time as the canal itself. The canal towpath and aqueduct are now part of a biking & hiking trail, and also used by snowmobiles. The I&M canal was designated a National Historic Landmark in 1964, and a National Heritage Corridor in 1984. The aqueduct/rail bridge can be found on Champlain St. 2 blocks south of East Norris Dr. (U.S. Rt.6) on the east side of Ottawa. As of Dec.08 there is a large amount of debris piled against the north side, due to flooding in Sept. Directly east of this bridge is the remains of a wood and concrete foot bridge that was partially demolished in the late 1970s. There are also the remnants of several bridges along the route of the I.T.S. in LaSalle County.
I'm going to retract my previous comment based on an excerpt from "The Electric Interurban Railways in America" by George Hilton and John Due