If in fact the police are going to go to a zero tolerance policy they are using a blunt instrument which wont improve road safety one iota.

What follows are my observations and other posters may have different experiences. I drive around 30,000 per year which is less than many drivers but, I suspect, still a lot more than most. A big percentage of this is on open roads. I generally set the cruise control and drive at a constant speed. The constant speed helps achieve a better fuel consumption.

Do I drive fast, no I don't. I drive to the conditions. Sometimes 100 kph is too fast on the open road. Do I break the speed limit while over taking, Yes, sometimes, to reduce the time exposed to danger. Without driving stupidly I can maintain a good average speed and a good fuel consumption.

With one exception the speedometer on every vehicle I have driven over the past few years has under read. The one exception was always correct compared the a GPS.

For the vehicles I drive, I nearly always check the indicated speed against a GPS, note the difference and then adjust my speed to allow for that difference.

Due to over reading speedometers and in some case lack of confidence a lot of drivers travel below the speed limit when it is quite safe to travel at the speed limit. They drive blissfully along at 90 to 95 kph often slowing well below this on hills or bends where it is still well and truly safe to drive at 100 kph.

Not only are these slow drivers unwittingly travelling below the speed limit many of them seem to think that since they are travelling at "the limit" they have the right to "police" the speed of the drivers following behind and not enable these drivers to pass when it's safe to do so. As a result they impede the travel of those travelling at the speed limit. 

To pass a vehicle within a reasonable distance (reduce the time in the on coming lane) you need to be travelling at least 10 kph faster than the vehicle you are passing. With the proposal for zero tolerance you will not be able to over take in what was previously a good safe overtaking space and/or you will be in the on coming lane for much longer then was previously the case. If using a passing lane fewer cars will be able to pass. All of this will increase the length of the line of traffic banked up up behind a slow driver thus increasing the frustration factor, which will lead to more accidents.

Also drivers will be watching their speedometer much more rather than the road and whats going on around them. As it is now some drivers (particularly slow drivers) struggle to be properly aware of their surroundings, particularly not being aware of what's going on behind them.

One thing I have noticed is that when I am following a slow vehicle that as a rule my fuel consumption increases markedly. This is because the slow vehicle doesn't maintain a steady speed, constantly accelerating and decelerating wasting fuel.