More than 8,000 drivers were caught speeding on an eight-mile stretch of the M1 in Derbyshire last year, statistics show.
Four cameras located between Tibshelf services and junction 29a were the county's most profitable in 2017 - with a total of 8,382 motorists caught breaking the speed limit on that section of the motorway.
The figures from Derbyshire Constabulary also show last year's fastest speeds were recorded on the same stretch, with the highest clocked at an eye-watering 128mph.
The minimum penalty for speeding is a £100 fine, meaning the four cameras generated at least £838,300 in 2017.
The maximum fine can be as high as £2,500 for the most serious offences so this figure could be much larger.
Cash raised from speeding fines goes directly to the Government.
A spokesman for IAM RoadSmart, a road safety charity, said: "In our view, the only numbers that should be important in relation to speed cameras are how many lives have they saved or whether crashes have been reduced.
"The job of a camera is to change driver behaviour not raise cash via a letter in the post days after the event.
"The best cameras catch no one because their message is self-explanatory and drivers can see instantly that there is a road safety problem that they should slow down for.
"Any camera consistently catching thousands of drivers should be reviewed immediately to ensure it is clearly signed, well-located and to identify a long-term engineering solution that will actually allow it to be removed.
"For motorway roadworks, average speed cameras tend to be far more effective than fixed ones as the vast majority of drivers comply with the temporary limits since they all know there is no escape."
Meanwhile, Darren Roberts, manager of the Casualty Reduction Enforcement Support Team for Derbyshire Constabulary, has confirmed new speed cameras on the M1 'smart motorway' in the county are switched on permanently - even when the illuminated warning signs are not.
Many motorists believe the cameras are only switched on when there is a variable speed limit in force.
Mr Roberts warned drivers they will be prosecuted if they are caught speeding above the normal 70mph limit or the reduced variable limits.