The core activity of road construction consists of lifting and moving large quantities of earth over distances varying from a few meters to up to a kilometre or more. Technological advance has provided workers with increasingly powerful tools to lift, transport, spread, shape and compact earth and gravel. This mechanisation of construction, involving the replacement of shovels, wheelbarrows and animal carts, by bulldozers, scrapers, graders and trucks and of course, ways to manage them, took about fifty years, and was essentially terminated before the second world war. It was stimulated by the scarcity and rising costs of labour, by the need to complete large infrastructure projects within short periods of time, and by advances in engine and power transmission design. Road construction technology is now mature, aimed to maximise the productivity of labour costing over thirty dollars an hour.
The problem is that in many developing countries today the conditions which forced this technological development no longer exist. Labour was in fact scarce and relatively expensive for a while in some countries in the 1950's (for example, 0,20 GBP per day in Ghana or about 12 GBP in today's purchasing power), so the desire to rapidly modernise infrastructure in the newly independent countries forced the perhaps premature transplantation of mechanised methods. Rapid population growth since then has now rendered labour abundant and wages have shrunk to a few dollars per day in many countries, far below those at the turn of the last century when the substitution of machinery for labour in western countries was most rapid. Sadly, in many developing countries they are also less than those of a couple of generations ago .
It should be added that road improvement projects in rural areas are small and remote. Heavy equipment is expensive to mobilise, difficult to deploy on site without causing excessive environmental damage and subject to excessive downtime due to delays in obtaining spares and fuel from the captal or even overseas. Finally, machinery, parts and fuel require foreign exchange which could be better spent on vital imports.
It is really rather absurd to persist in investing in labour-saving technology in developing countries, certainly at the level of low-volume rural roads. They are of course fully justified for large projects. For this reason construction techniques have been developed during the past thirty years which substitute labour for machinery when it is feasible to do so. This does not mean a return to pre-mechanised techniques but rather using technical ingenuity to seek an appropriate mixture of machinery and people, which unlike in conventional projects, can be men or women, taking account of their availability and wage levels, while drawing on modern construction management techniques to deploy them effectively.
Resistance to change has been fierce and the diffusion of labour-based methods has been slow. Modern construction technology is already mastered by public administrations and contractors in most countries while these new methods, involving the management of a much larger labour force, require changes in attitude as well as training. Large equipment fleets are owned by the public sector , relics of forgotten projects, old and in varying states of disrepair but still mutely clamouring to be used. Frequent breakdowns cause low productivity yet this, as well as the need to budget for their replacement, is often ignored in their comparing costs with those of labour-based methods. Contractors also tend to cling to their aging heavy equipment and the methods they impose. Sometimes they lease from the public sector, which does not always help.
All this all results in a strong bias towards preserving the status quo. Accepting new techniques requires an open mind and a willingness to learn among the engineers who must apply it. It also requires political will to resist pressure from vested interests and make the best use of the human resources they have at their disposal.