When it comes to the colors of bridges owned by the Illinois Department of Transportation (IDOT), there are only a few options available. Most steel beams supporting bridge decks are painted blue, green, gray, or brown. The official names for these colors are Interstate Green, Munsell Gray, Reddish Brown, and simply “blue.”
Mark D. Shaffer, Engineer of Bridge Design in IDOT’s Bureau of Bridges and Structures, explained that the use of four standard colors is based on their availability and prior testing and approval. He added an unofficial explanation: “I have been told the reason why we have those specific colors is that they are supposed to stand for sky, grass, clouds, and earth,” Shaffer said. “That always seemed kind of far-fetched to me, but that is what I have been told.”
The choice of color for a particular bridge is determined by the district where it is located. “Usually, the districts have a color that they like and that is what they use,” Shaffer said.
According to American Association of State Highway and Transportation Officials code cited by Shaffer, bridges are expected to be repainted twice during their anticipated 75-year lifespan—about every 25 years on average—but this can vary depending on conditions. “We expect them to be repainted every 25 years; however, we don’t normally repaint them unless they need it,” he said. For some structures this may happen sooner or later than average.
Sun exposure often leads to repainting front-facing beams due to ultraviolet light damage over time. Beam ends near joints may also require repainting because salty runoff from snow and ice control efforts can cause corrosion. Full repainting occurs when corrosion spreads further along the beams.
“When beam ends are repainted, the inspectors will note how much of the beam end is corroded. We will set up a painting contract to ensure that all the corrosion is removed,” Shaffer said. “Usually this is the last 5 or 10 feet of beams.”
There are exceptions regarding river crossings in Illinois where other colors might be used based on function or local preference.
For example, in 2022 the Interstate 255 Jefferson Barracks Bridge over the Mississippi River changed from reddish brown to gray under a project managed by Missouri’s Department of Transportation St. Louis District. Joseph J. Molinaro explained that gray was chosen because it makes inspections easier and helps identify issues more readily.
In Peoria’s District 4 area along I-74 Murray Baker Bridge over the Illinois River—which underwent major reconstruction as part of a $460 million upgrade in the early 2000s—the bridge color shifted from salmon to warm gray after community input favored something distinct from IDOT’s usual palette. Mark Eckhoff noted designers were not limited by standard choices given “a project of this magnificence should have its own unique color for its bridges.” The warm gray has since been used on other local bridges such as I-474 Shade-Lohmann bridges (repainted in 2017) with plans for Cedar Street Bridge as well.
Looking ahead at La Salle’s I-39 Abraham Lincoln Memorial Bridge—the state’s longest—District 3 Operations Engineer Junior Senat stated: “We do not plan on changing the color… It will remain green.”
