Worldwide traffic problems are becoming manifest in different forms. Densely populated countries regularly have to struggle with large traffic volumes on roads with capacities that are too low, causing large traffic jams. On the other hand, problems of mobility and inaccessibility are created because of low population densities and different settlement patterns in remote areas. In African and Asian countries, road planning is usually a part of an integrated development program in order to advance the common welfare and living conditions. For this purpose, plans for mobility within and accessibility of the countryside are integrated in the development program.
Traditionally, road planning focused on the construction of new roads and on the modernization of existing ones, in order to satisfy traffic demands. However, gradually it became clear that this way of planning insufficiently considers side effects of roads and traffic. Technological, economic, and social developments have caused new trends in the planning of roads , such as
• the importance of safety and consistency in design in each road category;
• the harmonization of the service conditions offered by different networks and road categories;
• the inclusion of side effects of traffic for local people (livability, which is negatively affected by noise and pollution) and for flora and fauna (habitat fragmentation by roads and their traffic).
Today, safety generally is considered to be one of the most important traffic issues. In the United States and in western European countries, traffic safety has increased significantly over the past decades, despite a considerable growth of traffic volume. However, this increase has slowed recently. The number of victims is still much too high. Differences between countries are considerable. A substantial further increase in safety requires an entirely new approach . In countries in transition, the number of traffic victims is relatively high, and traffic safety in these countries has worsened. The standard of the existing road network fails to cope with the present rapid growth of car ownership and the simultaneous technical upgrading of cars. Developing countries are well known by their relatively unfavorable traffic safety situation.
Emissions problems have diminished with the introduction of catalytic converters, especially in industrialized countries, but growing volumes of motor vehicles have increased the problem of traffic noise. This is mainly, but not only, an urban problem.
Outside of built-up areas, roads and traffic cause habitat fragmentation for flora and fauna. Four aspects of this habitat fragmentation are important :
1. destruction or alteration of habitat due to construction works;
2. disturbance of habitat along the roads by noise, etc.;
3. hindrance of movements caused by physical barriers related to the presence of roads;
For LTRs, aspects 3 and 4 are considered to be the most important ones . Both are barrier effects, especially affecting fauna. They force a separation of functional areas, such as living and reproduction areas or rest and food areas as well as kill the crossing animals. Both an increase of the overall stock of roads and growing traffic volumes intensify habitat fragmentation.
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