|Environmental Handbook Volume I: Introduction, Cross-sectoral Planning, Infrastructure (GTZ/BMZ, 1995, 592 pages)|
|16. Road building and maintenance, building of rural roads|
The term "road building" covers public roads and footways of all kinds inside and outside built-up areas that are used for the movement of persons and goods.
The roads involved will generally be two-lane rural roads or single or two-lane rural footways that are intended to establish a traffic link between two specified points or to open up a region in a practical way by providing a new or expanded transport network. For this reason we will not be considering here the special problems of urban roads or developments of the motorway type (such as the stress on the population in centres of population).
As dictated by purpose, volume of traffic, and the given natural morphological conditions in the landscapes to be crossed, the design standards (right-of-way width, vertical and horizontal alignment, structures, and carriageway pavements) that the planners elect to adopt in the light of vehicle characteristics will be more or less generous.
Despite the wide variations in topography, climate, hydrography, soil types and vegetation that exist, there are relatively standard rules for planning and construction that govern the three main stages of building a road:
- deposit a fill of the minimum height required using suitable soil that if possible is available from nearby sources,
- protect this fill with a system of passages through it and ditches to drain away rainwater and any constantly occurring surface water,
- pave the carriageway with bound (with cement, bituminous material, etc.) or unbound mineral layers in a manner suited to the wheel loads anticipated and their frequency of passage.
All roads require constant maintenance, though the amount will vary with heaviness of use (crown to be kept free of vegetation, drainage system to be kept fully operational, erosive damage to be made good where cut and fill methods were employed, carriageway to be repaired).