Roundabouts, small structures and small details

Solutions to road engineering problems involve how to conserve space, harmonize with the site and provide cheap and safe traffic solution. Since the contruction of the carrefour de l'arc the Triomphe (Paris) at the dawning of the 20th century, roundabouts are thought to be safer than both traffic circles and traditional intersections but they require a lot of space and here comes the task of the structural engineer.

The first example is a roundabout over a stream in a dense urban area. In this case the drainage requirements, a poor DPSH resistance of the soil and how to mix the bad quality old structure and the new one were the main causes of my headaches during the project phase.

The second example is placed in a rural landscape so I chose a green wall to respect the environment. The cost of this wall is about 120 € per square meter of covered surface which is more or less the cost of reinforced earth.

If Mies van Rohe is right, God is in the details and I totally agree in this case. A well designed roundabout can result in a complete disaster without the appropriate structures, lateral protection barriers and traffic signals. As for the last point, I encourage to borrow some of the ideas about signalling from the web site of Prof. Manuel Mateos and to use bigger and more understandable road signs.

Although the galvanized steel barrier (left) is the preferred solution by our administations, it seems clear that the classical New Jersey made of concrete (right) is safer in most of the accidents.

Left: Speed limit for roundabouts found in the Spanish norm 8.1 IC. Right: Alternative fonts proposed by Manuel Mateo.

Note: All the comments - even the caustic criticism - can be valuable on this point.