More than half of Britain's A roads have failed to be rated as safe in a study of 28,000 roads and motorways.
A quarter of motorways also rated poorly, the European road assessment programme (EuroRAP) found.
Single carriageway A roads were rated to be the most dangerous, with experts calling for better signs, lines, junctions and road surfaces.
The Department of Transport said its new road safety strategy would cut speed limits on dangerous roads.
The programme found that 58% of A roads it assessed were found to be either neutral for safety or poor.
Some roads have a persistently bad record, such as the winding A537 from Macclesfield to Buxton which had 27 accidents resulting in deaths or serious injuries over two years, many of them involving motorbikes.
A four-mile stretch on the A675 between Higher Walton and the M65 at junction three, in Lancashire, was also highlighted, with more than half of all fatal or serious collisions occurring at junctions.
Of the "persistently higher risk roads", eight out of 10 were around the Buxton, Sheffield, Macclesfield and Yorkshire and Humberside areas.
The report also noted the improvement made on a 27-mile stretch of road between Carmarthen and Llandovery in Wales where accidents were cut by more than 80%.
Dr Joanne Hill, director of the Road Safety Foundation which manages EuroRAP's work in the UK and Ireland, said: "It is the busy non-primary routes - the ones that take volumes of traffic at all hours between towns and villages across Britain - that the new survey shows represent the highest risk, accounting for 62% of all road deaths."
The Institute of Advanced Motorists said the design of many rural A roads actually made small errors in driving more likely to lead to accidents and fatalities.
Spokesman for the IAM Peter Rodger told the BBC News website there were lots of things that could be done to improve safety through good design.
"If you've got a reasonably wide single lane road with a junction, you can paint a section in the middle solely for people who want to turn right," he said.
"That way they're removed from the main flow of traffic.
"You can also install barriers along the sides of roads. Trees are particularly unforgiving if you crash into them, so if you've got a corner where you know lots of people leave the road you can install barriers in front of the trees to absorb the energy of an accident much more safely.
"You can also build roads to discourage overtaking. The crudest, most effective thing, like they do in Norway and Sweden, is simply to put barriers down the centre of the road."
Figures released on Thursday show that the number of deaths on UK roads fell to 2,538 last year - the lowest level since records began in 1926.
A Department for Transport spokesman said: "We've cut the number of people killed or seriously injured on the roads by more than a third since the mid-1990s.
"That means almost 17,000 fewer deaths or serious injuries in a year.
"But we know that safety on single carriageway A roads remains a problem, which is why our new road safety strategy sets out plans for local authorities to reduce the speed limit on the most dangerous of these roads where this will have the greatest impact on fatal crashes."