M25 at 40: slowest section revealed on Britain’s busiest motorway’s anniversary

The M25 isn’t broken – it’s only a small part that gives it a bad name. That’s the view of travel analytics firm Geotab which, on the 40th anniversary of the M25, found that eight of the orbital road’s 10 busiest sections can be found in just one condensed stretch of motorway.

Across a sample of 12 weeks picked between September 2025 and August 2026, Geotab says that 46 of the M25’s 58 directional sections experienced traffic posting an average speed of 80 per cent of the imposed speed limit. Yet eight of Britain's busiest motorway’s most congested sections were found to be concentrated within one area between J10 and J20.

Perhaps unsurprisingly, the slowest slither of the M25 is the Heathrow corridor between J15 and J16; Geotab’s data reveals the average speed here is a lowly 44.6 mph – roughly 64 per cent of the 70mph speed limit. Here, Geotab claims a three-minute journey can jump all the way to nine minutes depending on the time of day. Similarly, J12 to J11 heading anticlockwise for Thorpe and heading towards Chertsey averages just 68 per cent of the speed limit, making it one of the worst pinch points.

“Between Junctions 10 and 20, the M25 meets the M3, M4 and M40 and serves Heathrow, so long-distance freight, airport traffic and commuters are all joining, leaving and changing lanes within a few miles of each other,” explained Geotab vice president, Aaron Jarvis. “That constant merging is what slows the flow.”

“The M25 is easy to complain about, but the research shows how much businesses across the South East depend on it,” Jarvis continued. “For many operators, there simply isn’t a practical alternative.” Geotab surveyed 1,000 van drivers based in the South East and found that 84 per cent said that their businesses would not operate effectively without the M25.

Yet despite the M25 not being quite as problematic on the whole as one might have thought, four in five still feel that the motorway is less reliable than it was prior to the COVID-19 pandemic. With the vast majority (80 per cent) also stating that using alternative routes is worse, Geotab claims better management could be key to keeping traffic flowing smoothly.

“The findings point towards targeted interventions: quicker responses to incidents, better information for drivers, better coordination of roadworks and particular attention to the western M25, where congestion and unreliable journey times are most concentrated,” Geotab’s report reads.

Get even more from Auto Express, follow our channels...
• Google
• Reddit 
• Whatsapp