The Autobahn 7, Germany's longest highway, runs straight through Hamburg. Over the years, it's grown more and more congested, now carrying about 152,000 cars and trucks per day.

To deal with the increasing traffic, the city is turning to a pretty conventional solution: widening virtually the entire stretch of the highway that runs through the city.

But to deal with the noise — and the way that the highway has severed neighborhoods that were connected before it was built in the 1980s — Fast Company reports that the city has come to a pretty interesting solution: they're burying a few miles of the highway and covering it with parks, community gardens, and housing development.

The project, which is called the Hamburger Deckel and is projected to cost $800 million, comes after 20 years of lobbying from a local residents' initiative called "Ohne Dach ist Krach" (German for "No Roof, Too Much Racket"). Burying the highway is a practical way to meet a city noise abatement ordinance passed in 2005, as the sound barriers built in most places (including virtually everywhere in the US) can only cut down on noise by a factor of about half.

The tunnel project also has some other benefits: in covering what will be an eight-lane freeway, it'll provide a substantial amount of new parkland, along with space to build a neighborhood of 1700 homes. At its northern end, the new park will also link existing parkland, establishing a new greenbelt. Work is starting this year, and it's projected to be finished in 2022.

Of course, there's also another solution to eliminating traffic noise: tearing out urban highways entirely. In the US, Seattle is burying a downtown waterfront highway at a cost of $4.2 billion (and counting), and there's a pretty good case to be made that the city would have been better off removing the highway and replacing it with parks or pedestrian-friendly development.

But there are significant differences between the Hamburg and Seattle projects. One is that the Autobahn 7 is a crucial national highway that carries lots of traffic across the country — something that isn't true for Seattle's Alaskan Way Viaduct — making it much harder to tear down without major disruptions.

Additionally, Hamburg's project is less ambitious, in an engineering sense. Its highway is simply being slightly lowered, with a six-to-ten foot cap placed on top of it. Seattle is taking on the huge challenge of digging the widest deep-bore tunnel ever, 120 feet underground — which explains why the boring machine got stuck last year, halting construction until April at soonest and leading to cost over-runs.

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