Many rural roads are normally passable for maybe 95% of their length but may then turn into an impassable quagmire for the remaining 5% where they are crossed by watercourses or at low points in the alignment in wet weather.
Drainage and water crossing structures form a major part of the construction cost of a road which, depending on the topography, may account for up to 40% of the total cost. Once a road has been constructed the passability and maintenance cost are closely linked to the quality of the cross drainage provision for the road.
There are established reference sources for structures using the normal reinforced concrete techniques. However, little guidance is available concerning small structures, with respect to the optimum use of resources such as labour, local skills (which may include masonry and carpentry) and local materials and small enterprises, yet still achieving durable and adequate structures. Intelligent use of these resources will often produce the lowest cost structures in both initial and whole life cost terms. It is certainly inadvisable to blindly apply standards, practices and ‘rules of thumb’ derived from rich economies for use in developing countries where the balance of influential factors such as labour wage rates, availability and cost of standard materials and equipment, skills, access to finance and the support environment can be very different.
The Guide for Small Structures for Rural Roads (in 4 volumes) provides a review of proven alternative techniques optimising the use of local resources.
Many of the alternative techniques will have much lower Green House Gas emissions than reinforced concrete structures, which depend on significant amounts of high carbon dioxide equivalent (CO2e) inputs of cement and reinforcing steel, as well as often imported shuttering and steel fixing skills to a rural location.
