Transportation and Accessibility




The map of accessibility shows travel times (hours/days) between all points of the Earth to the “nearest” major city, defined as urban centres of 50 000 inhabitants or greater. It considered all modes of land and water transportation. Brighter colours indicate less time to move to urban centres, darker colours indicate more travel time. Globally, large voids correspond to circumpolar regions (e.g. Canada, Russia), rainforests (e.g. Amazon basin), high mountains (e.g. Tibetan plateau) and the arid and semi-arid regions of Africa, southwest Asia and interior Australia.
Source: Nelson A. in 14.


Infrastructure expansion is a major cause of land degradation

The imprint of the global road networks reflects a convergence of dynamic processes such as demographic changes, concentration of economies, land cover changes, and land use changes, including intensification of agriculture and urbanisation.
All of which affect the status and quality of the land and can exert combined pressures, potentially leading to land degradation.
The reach and intensity of human impacts extend over the entire planet. This is largely due to the extraordinary mobility of humans, as exemplified by economic globalisation. Local, regional and national economies are closely linked to the movement and transportation of goods and services across borders. Although other factors contribute, the geographic “connectedness” of any point on the Earth to all others is a useful indicator of its current economic standing and a predictor of future economic opportunity.
Access to basic infrastructure that sustains human wellbeing – such as water, sanitation, energy, schools, hospitals and markets – is one important measure of economic development.
Hence, nations worldwide strive to achieve a robust physical infrastructure as a basic and continuing focus of economic development. However, significant environmental costs accompany the development of physical infrastructure. Over the past century, the construction of roads and railways is one of the most widespread ways the natural landscape has been modified. Among their many impacts, roads lead to the destruction of natural vegetation, fragmentation of habitats, obstruction of animal migratory routes, the spread of exotic species, disruption of flows of rivers, alterations of natural biogeochemical cycles and increased accessibility by humans.
All these processes contribute to accumulated stress that affects the functioning of the land and can lead to degradation. Furthermore, increased human accessibility leads to an expansion of the “agriculture frontier”, especially in developing countries, since the obstacles to (e.g. cost of) marketing commodities grown in remote areas significantly decreases.
Accompanying this expansion of agricultural frontiers is the far larger infrastructure “footprint” when immigrants – often enticed by government incentives - settle to take advantage of cheap land and new economic opportunities. The development of Rondonia, Brazil, in the Amazon Basin is a well-known example of the frontier phenomenon.
In contrast to the more dramatic unfolding of agricultural frontiers, many parts of the less-developed world – such as arid and semi-arid lands – are already occupied by smallholder agriculturalists and pastoralists, but at low population densities. People there are often hugely dependent on the land and forced to overexploit the available resources. In such areas, the extension of infrastructure, especially roads, may lead to improvements in basic services to local populations and potentially enable access to local, regional and even international markets. Given the limitations of and challenges to maintaining livelihoods in remote arid and semi-arid regions, roads can also facilitate migration to urban areas where people seek employment, education and healthcare, etc.
While urbanisation generally serves national interests and there are incentives to promote it, migration to urban areas in some locations, such as sub-Saharan Africa, is often less than anticipated due to socio-economic and socio-cultural situations. Rural areas might see an increase in population but a delay in infrastructure development.
This may be related to inevitable disparities between urban and rural education opportunities as well as difficulties in returning expected remittances from urban to rural areas. However, as the economic power of globalisation increases, the pressure will likely grow to “relocate” some land uses (e.g. crop and animal agriculture) from areas with high production and environmental costs (e.g. Europe) to areas that have a comparative advantage (i.e. developing countries).

Logging and transportation roads for forest clearing visible from space in the Amazonian area of Rondonia in Brazil show a classic example of the expanding human impact along corridors. Images show a transition from 1984 to 2016.
Source: Landsat TM 1984

Logging and transportation roads for forest clearing visible from space in the Amazonian area of Rondonia in Brazil show a classic example of the expanding human impact along corridors. Images show a transition from 1984 to 2016.
Source: Landsat ETM 2001

Logging and transportation roads for forest clearing visible from space in the Amazonian area of Rondonia in Brazil show a classic example of the expanding human impact along corridors. Images show a transition from 1984 to 2016.
Source: Copernicus Sentinel 2 2016

Average accessibility time per continent.
Source: WAD3-JRC, based on A. Nelson [AP]