In an article from Spiegel Online:Controlled Chaos: European Cities Do Away with Traffic Signs Hans Monderman was able to get some press again for his idea of eliminating traffic signs.
The idea is this, eliminating signs forces drivers to be more careful, and therefore safer (they are less likely to hit someone). It also makes them slower, and therefore safer (they do less damage once they hit someone).
This is an interesting notion perhaps appropriate in some contexts (the street in front of my house e.g.). I do not believe it is a universally-applicable notion however (and I am not claiming Monderman does either).
The hierarchy of roads serves two purposes. One is access to land. I need a street in front of my property to get to and from my property (otherwise I am landlocked and require aircraft, tunnels, or boats). This street in residential areas is designed to be relatively slow moving, allowing travelers to reach their final destination (or leave their origin).
The second purpose is movement, I want to be able to go long distances between places at a low cost (time, money, etc.), and roads (e.g. highways) are important for this as well. Roads designed exclusively for this purpose include interstate highways, which are grade-separated and limited access.
The problem lies especially in roads that serve dual purposes, where non-locals want to move quickly, while locals want people to move slowly (or better yet, not at all except for the locals). Managing these roads requires especially creative solutions that are in many cases.
However, one needs to think about what problems traffic controls solved in the first place, why were they invented and deployed. A congested intersection without control, or with stop sign control, moves many fewer people per hour than one with traffic lights. If your objective is moving people, this is an important consideration.
Interestingly his ideas are supported both by liberatarians