The big signs along the highway—the ones announcing the next exit—are mounted on big bolts that are designed to split off if they're hit by a car going fast enough [1].
Our civilization is so complex that, not only do we have an extensive road system, to carry truckloads of Barbie dolls, laptops, and coffee beans, but we also have special infrastructure (signage) to support the road system. And that supporting signage infrastructure is sufficiently complex and important that there people dedicated to designing the posts that hold the signs, designing them so as to reduce the chance of death when something goes wrong and flies off the road.
Of course, the people who design the roads and the signs use tools, like CAD/CAM tools (not to mention email) which themselves constitute an infrastructure.
And as I mentioned the other day, the people who make things like email and CAD/CAM software, are in turn using tools: mainly programming languages (and their attendant compilers), but also IDEs, code-analysis tools, code generators, and so on. I like to think that we who design this class of product are building infrastructure for infrastructure for infrastructure for the modern world.
Of course, I work only on the theory of such infrastructure3, but I'm contributing nonetheless.
[1] Hayes, Brian. "Infrastructure: The Book of Everything for the Industrial Landscape."