They really ramped up automated radar deployment in 2003-2007, I spent 10 minutes trying to find data that would let me see at a glance if accidents went down more than usual starting in 2003 but didn't find anything straightforward.
Anecdotally, most people who speed just slow down at the traps, then accelerate back. I'm not sure that's much safer than going steady at the higher speed.
https://hal.archives-ouvertes.fr/hal-00430965/document
> This public policy has yielded remarkable road toll statistics. The number of fatalities has diminished by over 40% since 2002, and the authorities are speaking of 12,000 lives saved since the new policy was implemented. The number of injuries avoided is also considerable, even if the fatality figures are those that draw most attention from official decision makers and the media.
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The "slowing down for camera" behaviour might be less of aproblem, if camera locations are biased towards safety critical places. But it also has a fairly simple technical solution: average speed cameras. These work by timing vehicle sightings between two cameras.
You can automate it for much less than what traditional cop labour costs, and speeding ticket revenue would pay for the automation. If there was more enforcement, people would keep to the speed limits more frequently and there would be less stops. It's a control system with a feedback loop.