Research into anxiety levels of motorists on the M25 suggests the Dartford Crossing in Kent is the most stressful section of the motorway.
Drivers' stress levels rise when approaching the tolls, a survey says
Drivers have been compiling a "stress map" and travelling around the 117-mile orbital route to gauge which are the most frustrating stretches.
They found the Dartford Crossing was worst because motorists worried about having the right money for the toll.
Stress levels began to rise on the approach to the tunnel and the bridge.
'Road to Hell'
At Dartford, anxiety is said to increase as three lanes of traffic suddenly expand into eight lanes for the kiosks - and rises further as vehicles race away from the tolls.
The six drivers taking part in the study, including one woman, have already completed 32 circuits of the M25, which carries 200,000 vehicles each day.
The London orbital is said to have inspired the title track of guitarist Chris Rea's album, Road to Hell.
But Paul Watters, AA spokesman, said: "The M25 is badly maligned, but it has been a victim of its own success.
"It's brought vastly better journey times for people.
"Everyone forgets that before the M25 you had to travel through central London to drive from Kent to the Midlands."
Initial findings suggest driving clockwise around the M25 may be marginally less worrying than driving anti-clockwise, possibly because most drivers are right-handed and feel more comfortable turning the wheel in that direction.