The I-235 Freeway through Des Moines, Iowa is roughly 14 miles long, and was reconfigured and repaved over six years beginning in 2002. Three basket-handle arch pedestrian bridges were added over the freeway during this reconstruction. Concurrent with the freeway reconstruction, a four-lane arterial road was also built on the city’s south side, with one basket-handle arch traffic bridge as part of that project.

 

The lighting for all four bridges consisted of metal halide floodlighting accenting the bridge structures, and providing walkway lighting on the pedestrian bridges. The total connected lighting load for all four bridges was 27,339 watts.

 

The existing lighting required ongoing maintenance, and the close placement locations of the accent lighting to the bridge yielded a non-uniform illuminance. Routine maintenance of the pedestrian bridge’s lighting over an active freeway presented additional hazards and challenges.

 

The four bridges’ relighting consisted of an LED area type luminaire with high angle lateral distribution and rated for upward aiming in a wet location. A hinged stainless steel mounting stanchion was custom designed to mount at the existing locations, with the new LED luminaires affixed to each one. Supplemental safety cables attach the luminaire and mounting to the bridge structure in the event of a catastrophic failure. The assemblies’ hinging allows the fixtures to be raised to the bridge deck for servicing.

 

The total new connected lighting load for all four bridges is 6,554 watts, representing a 76% energy reduction, with a much greater uniformity and nearly doubled illuminance values.

 

An image of a basket-handle arch bridge is a component of The City of Des Moines’ logo, and the new bridge lighting serves to reinforce that impression during hours of darkness. The bridges are highly visible to visitors and residents alike, and a source of great community pride.