英语听力：自然百科 廊桥遗梦

Like dovetailed joints connected to the past, covered bridges line in the rivers in Vermont. Originally they were developed in Germany, Austria, and Switzerland centuries ago, when all bridges were made of wood, and those without roofs rotted away in the weather. Today Jan Levandowski restores those that still survive, and builds new ones.

"This is one of the five new ones I've built, but I've restored probably thirty. I think everyone finds bridges appealing though. Um, they like the idea of standing over water, gives them a romantic appeal that they’re nice to be in, they're cool, they're breezy and they're fun to beunderneath."

"Covered bridges are natural, I think, in Vermont, because of all the timber that the state had, and in most cases it's very easy to build, and local builders could construct these bridges. And that was important, because the towns didn’t have a lot of money, and they needed to do, be able to do everything pretty much themselves, which they did. You want something is going to last. The early bridges in Vermont were open-deck wooden structures, and they are fine, except they are going to rot. But the bridges are currently in its new as you know, but it replaced the bridges that are near 116 years. And as long as you keep it covered, and keep the rain and storms out of the, out of the truss work, it can last indefinitely."

They are remarkably strong. They can outlast even modern steel bridges which aresusceptible to rust, and their design remains unique. They are supported by wooden trusses that form interlocking systems of triangles that distribute the load and stiffen the bridge.

"To think of a truss, you must think of carrying a load from above rather than from underneath. It is a far more practical way of carrying the load, because you are able to control the exposure of thosestructural elements to the elements of the weather."

"Wooden bridges cost more initially than steel or concrete bridges, but cheaper than stone bridges. The other hand, they probably last, on the average, three times as long. So I think they are a good buy."

The old covered bridges of the countryside are disappearing, falling to age, flooding, even the occasional act of arson. Here and there however, a few keep standing through the seasons in years, spanning rivers and oceans of time.