The legislation permits visual obstructions only within certain boundaries and is defined under § 35b of the StVZO. These boundaries are determined using the 24m-measurement circle, as shown in the figure. The most important demands are:
The frontal visibility limit is to lie within a semicircle of 12 m radius.
The frontal "Visibility wedge" is to cut a chord > 9.5 m on the circle.
Obstructions may not exceed the limits defined in the graph on the right side.
When vision obstructing sections of width > 80 mm are present, the minimum centre distance measured as a chord on the vision semi-circle is to be at least 2.5m.
A maximum of 2 coverings within the visibility wedge,
A maximum of 6 coverings on the visibility semi-circle.