A well-designed regional road network consists of several mutually related hierarchical networks. First, there is the network of high-quality roads, such as motorways, to provide long-distance connections with high-speed travel. This is mostly a national network. Second, the network of regional highways connects regions with each other and with the first network. In countries of the Organization for Economic Cooperation and Development (OECD), these major roads only represent some 20% to 40% of the overall stock. In developing countries, this is much lower—some 5% [2]. So, the network of high-quality trunk roads only includes a relatively small part of a country's total road network. The majority of this network is the so-called low-traffic network, embracing the low-traffic roads (LTRs). Other terms, such as low-volume roads and minor rural roads, are also in use. In the following sections, LTR is used to mean roads with lower functions than the trunk roads. Both one-lane and two-lane LTRs and paved as well as unpaved LTRs appear. In developing countries, unpaved roads represent about two-thirds of the


= Motoway trunk Roads

Rural highway J - Low-Traffic Road

Figure 3.1. Coherence between networks of trunk roads and LTRs. Source: Reprinted by permission of the Wageningen Agricultural University.

network, excluding tracks that cannot be defined as roads [2]. Figure 3.1 illustrates the coherence between the networks of trunk roads and LTRs.

LTRs play a major role in the industrialized countries in promoting and facilitating the proper development of land and natural resources, serving the needs of local industry and promoting commercial, social, and cultural activity at both local and regional levels. In developing countries, roads are designed essentially to open up new resources, develop agriculture and mining, promote industry and commerce, and stimulate the social and cultural life of the regions [2].

In defining an LTR, several criteria may be used, including traffic volume, road function, administrative classification, and management and financing arrangements. LTRs are mainly local collector and access roads but they might also be of a higher road class. Traffic volumes on these roads is less than 1,500 (2,000 in certain exceptional cases) motor vehicles per day [2]. Among the network of LTRs, there are mainly local

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