The Road design handbook comprises four parts. `Basic criteria' addresses subjects that apply in general to the other three parts, each of which explores the design of one of the three road categories distinguished by the Sustainable safety of traffic concept, i.e. distributor roads, district access roads and estate access roads. There are two types of distributor roads: national and regional distributor roads. National distributor roads form the primary road network and are the key traffic provision for interregional movement within the country and between the associated economic and cultural centres. The regional distributor roads complement this network, ensuring a sufficiently dense network of distributor roads. Only the regional distributor roads are addressed in this Handbook, since the national distributor road is the priority of the flow function. Relatively quick flows of traffic are key to both road sections and intersections. The need to limit the number of possible traffic conflicts motivates the following requirements: split-level intersections, and preventing vehicles from crossing the traffic way reservation.