Will a wooden fence really sort out the noise pollution?
If only Alton had thought of that. They could've built one around the Roper's house.
Well... acoustics is complicated. That's as far as I can manage to boil it down. I took an acoustics course in university, but it's two years ago now. Let's see if I can remember the relevant bits...
Basically, sound is emitted as waves, like when you throw stones into quiet water. If the waves hit a hard enough surface, they will bounce back, otherwise they will propagate through whatever medium you put in front of them. Wood alone is not a very good "insulator", the sound waves will simply agitate the wood and continue the wave motion on the other side. A more porous material will dampen high-frequency sound waves a lot (since the wave motion will involve pushing air back and forth through lots of small pores, which creates friction that steals energy from the wave). A heavy, stiff material will dampen low-frequency waves (since the wave motion will transfer its energy to the material, whose stiffness will work against the motion and steal energy). Insulating against sound is all about stealing energy from the sound wave, really. There's a third method too that works with resonnance, but it's too complicated for me to explain here (especially when it's around midnight).
The closer to the source you put the sound insulation, the better. It's the same as blocking light, you need less effort to keep your room dark the closer to the lamp you put the cover. You can, of course, try to encapsulate the recipient of the noise (which is what is done with control rooms in noisy industry halls, for instance), but usually it's way more practical to insulate the source. At the source, you can even manipulate the direction of the sound (which is why trumpets look like they do), but only a few metres away, the waves would have bounced off enough surfaces to become omnidirectional and diffuse.
So in this case, the wooden fence serves two purposes: To give the sound source (the coaster train and its passengers) some insulation in one direction, and to "bounce back" the sound the fence can't absorb. In a closed environment, a one-sided sound barrier wouldn't work, the sound wave would simply bounce off some other surface and back in its original direction, but in open air, it will just dissipate away before it hits anything.
Also, it seems like the fence is covered with something on the "coaster side". Probably a material to enhance the reflectivity of sound, since again, wood on its own tends to absorb and re-emit a lot of the energy. This will have the side effect of making the coaster a lot louder to riders, though. Block sound from escaping in one direction, and you'll have twice as much of it going the other way.
Hope any of that made sense.
