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Science and technology
科學技術
Quieter traffic
更安靜的交通
When the rubber hits the road
當橡膠遇上公路
Turning old tyres into new roads can help cut noise pollution
把舊輪胎建成新式道路可以減少噪音污染
AROUND one heart attack in 50 in rich European countries is caused by chronic exposure to loud traffic, according to the World Health Organisation.
據世界衛生組織報道，在歐洲發達國家中，平均每50個人就會有一個由于持續暴露在交通噪音中而患上心臟病。
The ill-effects of noise pollution in such countries are second only to those from dirty air, says the WHO. Long-term exposure can cause hormonal imbalances as well as mental-health problems.
WHO還說，在這些國家，噪音污染產生的不良反應僅次于空氣污染，長期暴露不僅會造成激素失調，還會引發精神問題。
Roadside barriers can help dampen the racket, but they are expensive—up to $600,000 per kilometre—and they often serve as magnets for graffiti.
路邊聲屏障可以減少喧囂，但它們太貴了——每公里高達60萬美元，而且很容易變成亂涂亂畫的場所，
Besides, they work less well on windy days and are impractical along city streets. Happily, there is another option.
此外，它們在多風的時候效果并不好，更何況在城市街道邊安裝也不大現實。幸運的是，我們還有其他選擇。
By adding rubber “crumbs”, reclaimed from shredded tyres, to the bitumen and crushed stone used to make asphalt, engineers are designing quieter streets.
在瀝青和碎石里添加從輪胎碎片中回收的廢膠末，再鋪成柏油路，這樣工程師可以設計出更加安靜的街道。
First used experimentally in the 1960s, this rubberised, softer asphalt cuts traffic noise by around 25%.
第一條試驗性道路出現在20世紀60年代，這種加入橡膠而變得更柔軟的柏油路可以減少約25%的噪音，
Even better, it also lasts longer than the normal sort.
更棒的是它的壽命比普通路面更加持久。
Not surprisingly, rubberised asphalt is catching on.
參入橡膠的柏油路漸漸變得流行起來，
Enough tyres are recycled in America each year to produce 20,000 lane-miles of the stuff, enough to re-pave about 0.5% of America's roads, according to Liberty Tyre Recycling, a Pittsburgh firm that handles around a third of America's recycled tyres.
這并不奇怪，根據自由輪胎回收公司的說法，美國每年回收的輪胎足夠修建2萬英里的橡膠柏油路，足夠重新鋪設美國0.5%的公路。
Rubber roads are also popular in China, Brazil, Spain and Germany.
在中國、巴西、西班牙和德國，這種橡膠路同樣非常流行，
Their popularity could spread further, since it is now possible to make rubberised asphalt less expensively than the traditional sort.
由于現在可以把橡膠柏油路的成本控制得比傳統路面還低，所以這種趨勢會越來越流行。
That is because rubber can partially replace bitumen, the binding agent used to hold the crushed stones together in ordinary asphalt.
由于橡膠會部分替代瀝青，在傳統柏油里面，瀝青這種粘合劑的作用是把碎石裹在一起，
Bitumen is derived from oil, which means its price has risen over the past decade alongside that of crude oil.
而瀝青源于石油，這意味著過去十年其價格隨著原油價格的上漲而增加，
Discarded tyres, by contrast, are cheap and are likely to get cheaper.
相比之下，那些廢棄的輪胎不僅便宜，
In rich countries, around one tyre is thrown away per person per year.
而且會變得越來越便宜。在發達國家，平均每人每年都要扔掉一個輪胎，
They are piling up especially quickly in Europe, where dumping them into landfills was banned in 2006.
輪胎的累積在歐洲特別迅速，因為2006年歐洲禁止把它們倒入垃圾堆。
Rubberised asphalt keeps the noise down in a couple of ways.
橡膠柏油能減小噪音的兩個原因如下：
Pores between the stones in standard asphalt must be small, because if the gaps are too big the bitumen binding cannot do its job properly.
在標準柏油里，碎石之間的氣孔必須很小，如果縫隙太大，瀝青就不能正常約束碎石，
Adding rubber thickens the bitumen.
橡膠的加入可以使瀝青變厚，
That allows bigger pores, which help to trap and disperse sound waves.
允許更大的氣孔存在，這樣就有助于捕獲和分散聲波；
The rubberised bitumen itself is flexible and slightly springy, which enables it to absorb more unwanted sonic energy.
而參入了橡膠的瀝青本身也具有柔韌性和輕微的彈性，這可以使它吸收更多討厭的音波能量。
Shredded tyres are not the last word in exotic road toppings.
輪胎碎片并不是最新式的道路添加物，
A substance called PERS, or poro-elastic road surfacing, is being developed with a mix of private and public money in the European Union.
歐盟依靠公共資金和私人資金開發了一種叫PERS東西，
It is made from a blend of crushed rock, rubber and polyurethane, a synthetic plastic that replaces bitumen as the binding agent and allows even bigger pores in the road surface.
它由碎石、橡膠和聚氨酯制成，人造塑膠聚氨酯可以代替瀝青，因為這種粘合劑可以允許更大的氣孔存在于路面。
PERS is not cheap, costing around five times as much as rubberised asphalt.
PERS并不便宜，其成本幾乎是橡膠柏油的5倍，
But you get what you pay for:
但這完全物有所值，
tests suggest it can cut road noise in half.
據Luc Goubert測算，在一些特別吵鬧的地方可以減少一半的噪音。
In some particularly noisy areas, reckons Luc Goubert, who is co-ordinating the PERS project at the Belgian Road Research Centre in Brussels, the resulting boost to property values—and, therefore, land taxes—could help cover the cost.
這個結果也推動了周邊的房產價格—所以地稅或許可以幫助抵消掉成本。
