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Originally Posted by hiker47
The diameter is too small, especially for large trucks or trailers, and the use of the cobblestone is both contradiction to safety and traffic movement. The idea is great but the design faulty.
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The cobblestone truck apron is a fairly standard design, and is addressed in every design guideline that I have ever seen for roundabouts.
http://www.tfhrc.gov/safety/00-0676.pdf
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In cases where right-of-way, topography, or other constraints preclude the ability to expand the inscribed circle diameter, a mountable apron may be added to the outer edge of the central island. This provides additional paved area to allow the over-tracking of large semi-trailer vehicles on the central island without compromising the deflection for smaller vehicles. Exhibit 6-23 shows a typical central island with a traversable apron.
Where aprons are used, they should be designed so that they are traversable by trucks, but discourage passenger vehicles from using them. They should generally be 1 to 4 m (3 to 13 ft) wide and have a cross slope of 3 to 4 percent away from the central island. To discourage use by passenger vehicles, the outer edge of the apron should be raised a minimum of 30 mm (1.2 in) above the circulatory roadway surface (6). The apron should be constructed of colored and/or textured paving materials to differentiate it from the circulatory roadway. Care must be taken to ensure that delivery trucks will not experience load shifting as their rear trailer wheels track across the apron.
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