SATRAK Vehicle Tracking analysed data from 527,000 vehicles and found that the M4 was only slightly quicker with 30mph average speeds.
Cambridge was surprisingly the slowest city in the UK with vehicles averaging 13mph, closely followed by Hereford and London.
“It’s little surprise to find that the M25 is in fact the slowest motorway,” said Dan Walton of SATRAK Vehicle Tracking.
“I’ve heard of tailbacks stretching 12 miles in my time there so it’s of little surprise to me. It’s nice to see that people are taking care in many of our cities however, as these places are often busy and above all are not environments for speeding.”
Top 10 slowest motorways