The number of vehicle collisions has dropped by more than half since the introduction of average speed cameras on the A14 in Cambridge.
Cameras on the A14 measures average speed of vehicles
The cameras work out drivers' average speed between two fixed points.
In July and August, the two-month period monitored, there were eight crashes between Huntingdon and the M11 junction.
This compares to 21 for the same period in 2006, Cambridgeshire Police said. Speeding offences have also dropped.
They have fallen from 90 a week, on average, to about 16.
No-one was seriously hurt in the two month period but 12 people were treated for minor injuries.
In the same period in 2006 there were three serious injuries and 36 minor injuries.
Insp Matt Johnson said: "We are still at the early stages of this process and it would be too soon to speculate on the long term impact of the cameras but these initial figures are encouraging.
"Installing the cameras was never about making money through speeding fines but about reducing speed to save lives and reduce serious injuries."