Turn right... but not so much!

In his excellent blog, Jeff Atwood already talked several times about road signs in the perspective of user interface design. Indeed, as a professional software developer, I have occasionally to design interfaces (end-user panels, API, or frameworks); and I share the fascination of Jeff for road signs and for symbols usage in general.

In a previous article, I already made an analogy between road signs and software interfaces, about the necessity to design consistent models.

But even though you follow your own design rules and make a consistent interface, you still have make a proper usage of it. Let's continue our analogy with traffic signs and look at the following picture I took recently there.

So what? Obviously, you must turn right soon. But why installing two nearly identical traffic signs located at 10 meters from each other. The first sign indicates that the road turns 90° right; but a few meters later, it's only 45°.

According to the local driving rules (Page 121), the two signs have actually the same meaning: they indicate to the drivers the obligatory way(s) to follow according to the direction indicated by the arrow. So in fact, I cannot see any logical nor legal reason for the presence of those signs with a different arrow.

This example is a perfect illustration of an interface with a good design (simple sign intuitively understandable) but used improperly or inconsistently. Or did I miss something ?