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Network analyst firm Streetwave have published the results from a new study they’ve just conducted, which examined the mobile network coverage and mobile broadband (4G, 5G) performance of EE, Vodafone, Three UK and O2 across the entire M4 motorway from Cardiff to London – a 127-minute journey.
The live and admittedly somewhat anecdotal study, which used Streetwave’s portable network measurement and monitoring kit placed in a Toyota Aygo on 3rd August 2026, found that “most” of the mobile operators delivered high levels of ‘Basic Coverage‘ along the M4 motorway (see below for the definition). The M4 is the third-longest motorway in the United Kingdom, running from West London to Southwest Wales
Streetwave typically defines Basic Coverage as reflecting locations where the mobile network provides users with data speeds of above 1Mbps download, 0.5Mbps upload, and below 100ms (milliseconds) of latency (i.e. supporting only the most basic of use cases or needs).
Overall EE delivered the strongest result and were closely followed by Vodafone and Three UK, while O2 were by far the poorest. Most of the poor coverage areas for the latter came in multiple smaller segments as opposed to long stretches – particularly between Swindon and Reading.
M4 Motorway – Mobile Basic Coverage Scores
➤ EE – 97%
➤ Vodafone – 95%
➤ Three UK – 93%
➤ O2 – 78%
Time each network fell below the ‘Basic Coverage’ threshold
➤ EE – 4 minutes
➤ Vodafone – 6 minutes
➤ Three UK – 9 minutes
➤ O2 – 28 minutes
Such figures are useful for business travellers who may need to make calls or passengers who want to use the mobile broadband connectivity on their devices. But in that respect it would have been nice to see the ‘Good Coverage’ scores for each operator too, which set a higher performance bar for data connectivity.