Infrastructure

I've always been fascinated by how things work--what happens to the water from your bath after it goes down the drain, how do little rods of enriched uranium make the TV work and the lights turn on, how do enormous heavy airplanes get themselves, their passengers, and (in bygone days) their highly improbable food up in the air, and so on. I've found that other people tend to be interested in this sort of thing as well, although perhaps less enthusiastic than myself, so I'll share one of the interesting how-it's-done stories I've recently come across.

In the past weeks on my commute to and from work and school I've watched Martin Luther King Boulevard slowly but surely being repaved.

This kind of thing only happens at night, for obvious reasons: one, there are fewer people needing to use the road while it's being worked on, and two, the machines they use are far too cool to see the light of day. If you've never seen how it's done, the magical disappearance and reappearance of the road surface can be pretty puzzling. Allow me to explain.

Those of you who've ever kept an aquarium containing an algae-eating snail employed to keep the glass clean will already understand the process by which the road surface is removed. Remember watching the snail's bizarre little mouthparts scraping a clean line along the glass? It (and its friends the rest of the gastropods, including the Giant African Land Snail and the conch) is equipped with a thing called a radula which is basically a small organic emery board, with which it scrape-scrape-scrapes its dinner off whatever it happens to be walking on at the time. If you ever pick up a snail in the garden or at the seashore and wait for it to chill out enough to come back out of its shell, you will feel the radula scraping away at your hand. It tickles. I would not, however, recommend trying this with a large snail; they can be quite forceful in their radulation.

The machine that takes off the top two inches of the road surface is doing exactly the same thing as the snail. It crawls along not on a muscular head-foot but on two impressive-looking tank tracks, and between these a grinding mechanism is dragged along the road, scraping off the asphalt in a strip the width of a lane as it goes. The bits of road are then spat out via an overhead conveyor belt into a dump truck rumbling along at walking pace in front of the machine. It's a pretty powerful sight.

Once the radulation of a lane is complete, then the shiny new asphalt is laid down. This is done by a sort of modified and heated dump truck which dribbles the hot tar-and-gravel mix behind it, followed by a machine that presses down and smoothes over the new road surface. Voilà: beautiful smooth black road, laid down lane by lane, night by night. There's a bit in the movie Cars where a character has just completed repaving a damaged stretch of road, and the beauty of the new surface inspires Luigi the Fiat to exclaim "It's like it was paved by angels!"

Angels with a radula.