Why Did Engineers Fly From Around the World to Study This One Chicago Bridge? | The Why Behind It Ep

At 1440 West Cortland Street, where a modest road crosses the North Branch of the Chicago River, there is a bridge that changed how cities around the world cross their waterways. It doesn't look like a revolution. It has a wooden bridge-tender's tower. Its gear rack is exposed on the outside of the trusses. It has decorative finials and ornate plaques that later bridges in the same city would abandon for something more restrained. It looks, in other words, like exactly what it is: a prototype. This episode tells the story of how that prototype came to be — and why it mattered so far beyond the river it crosses. In the late 1890s, Chicago was a city with a problem. Its existing movable bridges were destroying their own foundations. The soft, swampy ground that Chicago is built on couldn't handle the shifting loads that the popular Scherzer rolling-lift bascule design placed on its abutments. And every time the city built one of those bridges, it paid royalties to a patent holder. Chicago needed a better design — one suited to its geology, and one it could build without writing a check to a competitor. City Engineer John Ericson directed a thorough international survey of movable bridge technology. His team — including Edward Wilmann, Alexander von Babo, Karl Lehman, and Thomas Pihlfeldt — studied what was being built in the United States and in Europe, including London's Tower Bridge, which had demonstrated the fixed-trunnion bascule principle in a high-profile, patent-free application. A Board of Consulting Engineers, including the prominent Ralph Modjeski, provided independent review. The result was a fixed-trunnion bascule design: a bridge whose moving leaf rotates around a fixed pin rather than rolling back on a curved track, keeping the center of gravity stable and placing consistent, predictable loads on the foundations. It was mechanically better suited to Chicago's soil. And it was designed around a principle the city's engineers believed they could build without paying royalties. The first bridge built to that design opened at Cortland Street in 1902. According to the American Society of Civil Engineers, it became the model for 53 of Chicago's 54 movable bridges. Engineers from around the world came to study it. The design spread to cities on multiple continents. But the story has complications. Milwaukee completed a bascule bridge weeks earlier. A patent lawsuit from engineer Joseph Strauss — later famous as the lead engineer of the Golden Gate Bridge — eventually cost Chicago $350,000, a painful irony for a design built specifically to avoid patent fees. And von Babo, one of the original designers, later patented an improvement to the very bridge type he helped create — moving the gear rack from the outside of the trusses to the inside. The exposed rack on Cortland Street is the artifact of a moment before that insight arrived. The bridge was designated an ASCE Civil Engineering Landmark in 1981 and a Chicago Landmark in 1991. It is currently undergoing a major restoration, closed since late 2025 with reopening expected in 2027. This is the why behind the Cortland Street Drawbridge: a city tried to save money on patent royalties, commissioned its engineers to do something better, and accidentally produced a global standard for movable bridge design. The bridge that started it all is still there — still opening for river traffic, still carrying the visible marks of being first. --- Sources & further reading [ASCE Historic Landmark – Cortland Street Drawbridge](https://www.asce.org/about-civil-engi...) [Wikipedia – Cortland Street Drawbridge](https://en.wikipedia.org/wiki/Cortlan...) [Wikipedia – Bascule bridge](https://en.wikipedia.org/wiki/Bascule...) [Chicago Landmarks designation](https://webapps1.chicago.gov/landmark...) [Structurae – Cortland Street Bridge](https://structurae.net/en/structures/...) [Historic Bridges – Cortland Street](https://historicbridges.org/bridges/b...) [Preservation Chicago – Cortland Street Bridge restoration](https://www.preservationchicago.org/w...) [Chicago Architecture Center – Chicago's movable bridges](https://www.architecture.org/online-r...) [Block Club Chicago – Bridge closing until 2027](https://blockclubchicago.org/2025/09/...)