The NZ Police speed enforcement guide states:
"When speed camera enforcement is taking place in the area of passing lanes, vehicles should not be targeted within 250 (two hundred and fifty) metres of the finish of any passing lane."
Paula Rose has explained it as follows:
"The policy was introduced to reduce the risk of vehicle crashes and the consequences of those crashes. The merging of vehicles at the ends of passing lanes is potentially hazardous. It requires vehicles to travel at similar speeds and merge 'like a zip'. Prior to this policy being introduced, there were reports of drivers in the process of merging suddenly braking and taking evasive action when they saw a speed camera vehicle ahead. These driver reactions led to higher risks of vehicle crashes than vehicle speeds alone. To minimise that increased crash risk, the policy was introduced to take the speed camera vehicles away from the immediate vision of drivers in the process of merging."
In another thread one of our resident traffic police officers wrote:
However, mobile radar enforcement from marked cars increases the risks Rose sought to minimise. In a country with just 2 degrees of separation it would not take many tickets to be issued in this way for word to get around. Once people become aware that marked police vehicles are deploying speed detection devices at the end of passing lanes they are likely to take the same risky evasive action rather than complete their overtaking manoeuvres safely every time such a vehicle approaches, regardless of whether it is operating a speed detection device or not. This would actually create more accident risks than operating visible speed cameras at these sites.
I have used this argument as one part of a many-faceted defense I have successfully deployed on the rare occasions of receiving speeding allegations in passing lanes. However, I do not believe it goes far enough. For a variety of reasons, safety being at the fore, I believe that the speed limit tolerance throughout entire passing lanes should be 40% higher than the actual speed limit, but what do you think?