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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Video gamer Felix Kjellberg, known as PewDiePie, suggested changes to YouTube's algorithms had affected the discoverability of creators' content.
On Tuesday, a Forbes report named the Swedish gamer who now lives in the UK as the highest-earning YouTuber.
YouTube told the BBC it had not made any changes to its "suggested videos" algorithms.
However, other video-makers have reported the same problem, with new videos being viewed fewer times than old content.
The "suggested videos" feed appears when a video is being watched, and recommends more content to watch.
Mr Kjellberg said the feed usually accounted for more than 30% of his video traffic, but in recent weeks it had suddenly fallen to under 1%, signalling an undisclosed algorithm change.
Other criticisms aimed at YouTube included suggestions that:
Film-makers have argued that YouTube has made it more difficult for fans to keep track of their latest uploads, and for new viewers to discover their content, since the platform was acquired by Google.
In a video uploaded on Friday, video gamer Mr Kjellberg said he would delete his channel when it reached 50 million subscribers as a result of his frustration with the platform.
His channel, currently the most-followed on the video-sharing site, is about 200,000 subscribers short of that target.
However, when asked by the BBC, YouTube denied that it had made any changes to its algorithms in recent months.
It added that it had found no evidence that people were being unsubscribed from channels they followed.
A spokeswoman said: "Some creators have expressed concerns around a drop in their subscriber numbers.
"We've done an extensive review and found there have been no decreases in creators' subscriber numbers beyond what normally happens when viewers either unsubscribe from a creator's channel or when YouTube removes spammed subscribers."
Mr Kjellberg is currently producing new episodes of his YouTube-financed series Scare PewDiePie, and on Tuesday topped Forbes' list of highest-paid YouTube stars for the second year in a row.
His PewDiePie gaming channel is likely to reach 50 million subscribers in a matter of days.
Mr Kjellberg suggested at that stage he would "start fresh" with a new channel, although some have taken his claim as light-hearted.
Source: Forbes
A global map of areas without roads shows large tracts of wilderness remain unprotected.
[NEXT_CONCEPT]
YouTube has denied making changes to its algorithms, after its most popular star said he would delete his channel.