Around 130,000 vehicles daily thunder along the A7 highway north of the Elbe river tunnel in Hamburg, Germany, noisily dividing the city. To eliminate this blight, contractors are building a vegetation-covered concrete box along more than 1.4 miles of highway in the busy Altona downtown district while keeping traffic flowing.
Technically, building the roughly 20-ft-tall, 138-ft-wide box "is not difficult," says Andreas Stemmer, business manager with the northeast German unit of project contractor Hochtief Infrastructure GmbH. The challenge is casting three hefty parallel walls along the highway and roofing them with 4-ft-deep slabs while keeping eight lanes open, he adds.