The new bridge took just over 2 years to complete. The finished structure is a masterpiece of urban architecture. The bridge looks nice, and it makes a statement. It is not dressed up, yet it looks very ornate. More importantly, it was built to do a job, and does that job so well that it still a key river crossing in downtown Saint Paul some 80 years later. The Robert Street Bridge was listed on the National Register of Historic Places in 1989. That same year, the bridge was extensively refurbished.
One feature of the bridge is that it appears to fit so well to its surroundings. Perhaps the reason for that is that the bridge was so difficult to fit around all the obstacles at that location. This includes having to be high enough for river boat traffic, low enough to meet the low grade south of the river without having too steep of grade (as required by street cars), it has to be high enough for trains to pass under, yet it had to match the height of Kellogg Blvd. The result is that the bridge design was dictated by each of these constraints.
The key feature of the Robert Street Bridge is the large rainbow arch. A rainbow arch has parts of the arch both below and above the traffic deck. It is a rather unusual bridge style. It was selected because concrete arches were the style of the day. But if the entire arch had been below the traffic deck, too much of the arch would have been in the way of river navigation traffic. The rainbow arch allowed the navigation channel to be maintained wider, and also put part of the arch above the traffic deck for bridge traffic to see.
The six secondary arch spans consist of five individual concrete arches, while the main span has only 2 individual arches. The reason is the rainbow style arch. There was no way to add more arches above the roadway without using up much of the width of the roadway. As a result, engineers designed a steel structure that sits under the main span to help support the roadway over the main span.
The photo above shows a good view of the main span rainbow arch. Notice that there is steel work under the bridge deck to help support the roadway. Also notice the Great Western railroad lift bridge behind the Robert Street Bridge. The railroad bridge was built many years before the Robert Street Bridge.