Some 5,540 miles of road - representing about two per cent of all roads - do not have coverage for calls from any of the country’s four mobile networks, the RAC Foundation found.
The top 10 local authorities most affected include Highland (910 miles), Powys (411 miles) and Cumbria (296 miles). North Yorkshire weighs in at sixth place with 219 miles lacking coverage.
A further 44,368 miles of road have only partial voice coverage, with not all operators providing a signal. This is 18 per cent of all roads.
Motorists who rely on their smartphones to access the internet for route planning and to check for congestion could get into difficulty on the 5,452 miles of road with a complete absence of 3G coverage.
An additional 66,619 miles are only covered for 3G by some operators.
In terms of 4G, just 51% of the road network has full coverage.
The research was based on analysis of data published by communications regulator Ofcom.
RAC Foundation director Steve Gooding said: “The good news is that mobile coverage has improved a great deal across our road network.
“On our motorways, which carry around a fifth of all traffic, every mile should now have voice and basic data coverage plus a 4G signal for all but a couple of miles.
“As rapidly as the technology has advanced, so too have our expectations of enjoying uninterrupted connectivity.
“Hopes are high that autonomous and connected vehicles will make our roads safer and help cut congestion, but that is dependent on those vehicles being able to communicate with each other and the infrastructure around them.
“This analysis shows that there is still work to be done to make constant and comprehensive coverage a reality.”
The local authority areas with the most miles of road lacking any mobile signal are:
1. Highland (910 miles of road with no coverage)
2. Powys (411 miles)
3. Argyll & Bute (388 miles)
4. Cumbria (296 miles)
5. Dumfries & Galloway (266 miles)
6. North Yorkshire (219 miles)
7. Gwynedd (213 miles)
8. Na h-Eileanan Siar (207 miles)
9. Scottish Borders (192 miles)
10. Devon (190 miles)