The most congested stretch of motorway in the UK is the M1 through Hertfordshire and Bedfordshire, a report has found.
Satellite navigation firm Trafficmaster blamed work to widen the M1 for serious traffic hold ups between J6A at Bricket Wood, Herts and J11 near Luton, Beds.
It said more than half of the M25 was also a congestion hotspot, particularly through Surrey to J20 for Watford.
It named J21 to J28 at Brentwood in Essex as the third worst for hold ups.
Congestion was measured in the 12 months up to April 2007 for the report by Trafficmaster.
RAC Foundation executive director Edmund King urged drivers to "get smarter" by using traffic information and in-car technology to avoid jams.
TOP FIVE CONGESTION HOTSPOTS
"Travelling out of the peak or working from home one day a week can have great benefits for the economy and environment," he added.
Trafficmaster spokesman Philip Hale said: "We all know where our local congestion blackspots are.
"The problem is we all continue to use these roads when they're most congested, despite knowing we're likely to hit a traffic jam."
The report also highlighted how using alternative routes can save time.
Mr Hale said the first step in tackling the problem was to identify it and avoid it.
"You can use alternative routes to literally save hours," he said.
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