Left-to-Right Flipper Bridge

Time to revisit one of my favorite topics: crystal grain boundaries and the limits of annealing.

Of course you know what I’m really talking about is driving. Specifically: which side of the road do you drive on? Driving standards (any standards, really) make me think of polycrystalline solids, because they are assembled from an earlier chaotic and somewhat fluid state. First, people are driving all over the place, but if you and I live close to each other, then we’ll come to a social accommodation. Let’s agree to both stick to the right side of the road, and life will be much easier. Local conditions favor alignment of standards and these standards spread. But eventually you get two big pools of people, the left-drivers and the right-drivers, growing together, and they meet at a grain boundary. Despite the nuisance of life at the boundary, the standards have solidified, and it’s very difficult to change them. Behold, the grain boundaries of the driving world.

Sometimes, grains can realign in a process similar to annealing. The famous example of this in driving standards is Sweden: in 1967, they switched from left to right, bringing continental Europe under one standard. But this was just the last act in a long list of such changes. It works the other way too: Okinawa switched from right to left in 1978 and Samoa did the same thing only last year.

What happens at these grain boundaries? In a small economy without much traffic, it’s not a big deal. But it gets to be a problem as trade grows. One look at that map shows some long borders in places experiencing significant economic growth. This all brings me to Hong Kong and a report I saw on the Fast Company site: Ingenious Flipper Bridge Melds Left-Side Drivers With Right-Side Drivers. Why not just have the bridge do the flipping for you? Sadly, the bridge is notional. They didn’t win the design competition. But it’s still intriguing. And it turns out, such bridges really exist, as Wikipedia happily informs us. Here is a map of the Lotus Bridge in Macao. Trace the curves. That’s as easy as life at the crystalline grain boundary gets.

Which side of the road?

The British drive on the left; Americans drive on the right. Simple enough. Since you can’t drive directly from here to there, you don’t have to worry about switching in mid-road somewhere. The Channel Tunnel goes from England to France (where they drive on the right), but you don’t actually drive through the tunnel, so no lane-switching problems ensue. If you look at a list of all the places in the world where they drive on the left, you’ll see that it’s a fair indication of the former extent of the British Empire. Islands like New Zealand and Sri Lanka, like England itself, can be self-contained zones of left-driving. But what about India? Left-driving India is connected by the Eurasian landmass to right-driving France. If you get in a car in Hyderabad and drive to Marseilles, somewhere you have to switch. What is that like?

I found the answer on an excellent site called Which side of the road do they drive on? Put together by Brian Lucas, it even has a world map that reveals the thing I was curious to see: there are enormous frontiers between countries that drive on opposite sides. At the Khyber Pass on the border between Pakistan and Afghanistan, for example, you have to switch sides. What are these border crossings like? Lucas is kind enough to have compiled some answers.

It’s so satisfying to be puzzled about an obscure topic and find an extensively documented well-maintained web page about that very thing.