Highway construction occurs nowadays mainly through widening of existing roads rather than building new roads. This article documents that highway widenings considerably reduce congestion in the short run, defined here as 6 years. Using longitudinal microdata from highway detector loops in the Netherlands, we find substantial travel time savings. These savings occur despite strong increases in traffic flow. The welfare benefits in the short run already cover 40% of the widenings’ investment costs. Our article contributes to an explanation why countries invest in roadworks even when the fundamental law of congestion predicts that travel savings disappear in the long run.

中文翻译：

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高速公路拓宽会减少拥堵吗？

现在的高速公路建设主要是通过拓宽现有道路而不是建造新道路。这篇文章记录了高速公路拓宽在短期内显着减少拥堵，这里定义为 6 年。使用来自荷兰高速公路探测器环路的纵向微数据，我们发现可以节省大量的旅行时间。尽管交通流量大幅增加，但这些节省还是发生了。短期内的福利收益已经覆盖拓宽投资成本的40%。我们的文章有助于解释为什么即使拥堵的基本法则预测旅行节省从长远来看会消失，各国仍会投资于道路工程。