Love this bridge! I had heard rumors that the city was going to destroy it.. Time will tell!
Might have something to do with this:
"During the construction of the viaduct (Los Angeles River), an on-site plant was used to supply the concrete for construction (of the bridge). However, the quality of the concrete turned out to have a high alkali content and lead to an alkali-silica reaction which creates cracks in the concrete and saps the strength of the structure.
Current estimates are that the viaduct has a 70% probability of collapse due to a major earthquake within 50 years. 
It is one of the only historic LA River bridges to suffer from ASR."