International recognition and protection of such areas is urgently needed to halt their continued loss, say scientists.
Roads may introduce many problems to nature, including deforestation, pollution and risks to wildlife.
Areas untouched by roads do not have adequate protection in most countries, researchers report in Science journal.
"We have produced a global map of road less areas," said lead researcher Pierre Ibisch, of Eberswalde University for Sustainable Development, in Germany.
"And this map shows that Earth's landscapes are shattered into more than 600 thousand fragments.
"We used a huge dataset of 36 million km of roads for producing this map."
Roads are important for economic development, but they have a number of potential environmental impacts, including deforestation, chemical pollution, and noise disturbance.
To gain a better understanding of the impact of road systems, scientists analysed two global datasets, OpenStreetMap and gRoads. They also reviewed 282 publications.
The map found that about 80% of the Earth's land surface remains without roads.
However, more than half of the 600,000 fragments created by roads are less than 1 sq km.
Only 7% are larger than 100 sq km (400 sq miles) - that's about the size of the island of Montserrat.
As roads continue to expand there is an urgent need for a global strategy for the conservation, restoration and monitoring of areas without roads and the ecosystems they represent, say scientists from 12 institutions in six countries.
Few countries have legislation that protects areas that are not fragmented by roads.
And in much of Europe and North America these areas have already been lost.
However, in Australia, for example, untouched landscapes such as the Blue Mountains only hours from Sydney still exist.
Dr Ibisch told BBC News: ''We see these road less areas as areas with an inherent value; something that merits being seen as a conservation target in its own right.''
Co-researcher Monika Hoffmann added: "Road less areas are still overestimated and many of them are reduced in size."
The research is published in the journal Science.
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A global map of areas without roads shows large tracts of wilderness remain unprotected.