These problems will only get worse as skies get more crowded.

上述的这些问题会随着飞机越来越多而变得更严重。

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Science has made our lives more comfortable and our machines more efficient, but it has also made our streets and skies more crowded and our wars more deadly.

科学使我们的生活更加美好，使我们的机器更加有效，但是，科学也使我们的街道和天空更加拥挤，使我们的战争具有更大的杀伤性。

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MARK: But it's a crowded city, with grey skies. It's expensive. It rains. But it's beautiful. Everything here's cheaper and we've got great weather.

但是这是个拥挤的城市，伴随着灰色的天空。很贵。下雨了。但是很漂亮。这里的一切都很便宜，而且我们拥有很好的天气。

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President Bush said other steps were under consideration to reduce crowded skies, such as charging airlines higher landing and takeoff fees at peak hours, and auctioning off landing and takeoff rights to the highest bidder.

NPR: Bush Announces Plans to Ease Air Travel Delays

The decline in travel because of the recession made airports and the skies less crowded, reducing flight delays and cancellations when bad weather or other problems forced airlines to thin out schedules.

WSJ: An Airline Report Card: Fewer Delays, Hassles Last Year, but Bumpy Times May Be Ahead

As the skies become more crowded, technology could be used to enable the size of such "safety spheres" to be reduced - or rather, to allow planes to fly closer to each other.

BBC: Sowing the seeds of tomorrow's aircraft