'Monofunctionality' is one of the principles of the Dutch system of Sustainable Safety.

This principle means that every single road and street in the Netherlands has to be assigned a single function, by law, either -

  • Access roads - the 'end destinations' for journeys, places where people live, work, shop, relax, and so on.
  • Through roads - for fast traffic, travelling longer distances, in large volumes. Motorways, trunk roads, bypasses, and so on.
  • Distributor roads - which connect up access roads, and link them to through roads (and vice versa).

Monofunctionality is actually a British idea, originating with 1963's Traffic in Towns report, quoted below.

The need for a hierarchy of distributors. The function of the distributory network is to canalise the longer movements from locality to locality. The links of the network should therefore be designed for swift, efficient movement. This means that they cannot also be used for giving direct access to buildings, nor even to minor roads serving the buildings, because the constant frequency of the junctions would give rise to traffic dangers and disturb the efficiency of the road. It is therefore necessary to introduce the idea of a 'hierarchy' of distributors, whereby important distributors feed down down through distributors of lesser category to the minor roads which give access to the buildings... Basically, however, there are only two kinds of roads – distributors designed for movement, and access roads to serve the buildings.