Visual Thinking: The Hidden Gifts of People Who Think in Pictures, Patterns, and Abstractions

by Temple Grandin

The design of the Golden Gate Bridge is far superior to that of the Tacoma Narrows Bridge, but an entirely different kind of disaster was averted in 1987, when the Golden Gate celebrated its golden anniversary. To commemorate the occasion, San Francisco allowed 300,000 people to walk across it, with 500,000 more hoping to do the same. The turnout was ten times what had been expected, and people were packed shoulder to shoulder for the entire 1.7-mile length of the bridge. As a result, the bridge deck sagged a full seven feet until the people were removed and the overflow crowd was, thankfully, turned away. The problem wasn’t poor maintenance; the bridge had been well maintained, which certainly helped to avert disaster. And it wasn’t a problem of design. As a suspension bridge, the structure was engineered to bend and move, and while this was the biggest load the bridge had seen, “it did not exceed the design load capacity of the bridge,” as engineer Mark Ketchum pointed out. In this case, the problem was the math. According to Stephen Tung of the San Jose Mercury News, while the weight of the individuals on the bridge was unknown, “if the average person weighs 150 pounds and occupies 2.5 square foot in a crowd . . . that’s more than double the weight of cars in bumper-to-bumper traffic.” Had the additional people been allowed access, there would have been a catastrophic tragedy.