The cameras work by measuring the time it takes to drive between two points and then calculating the vehicle's average speed.

If it's higher than the speed limit for the length of road the driver will cop a fine in the mail for speeding.

But, taking the cameras just out of Bathurst between Raglan and Meadow Flat on the Great Western Highway as an example, 30 seconds is the difference between being booked for speeding or getting through on time.

The cameras are about 25km apart and with an average of 100kmh, which is the speed limit on that section of road, the time allowed is 15 minutes but it's almost impossible for a truck to average 100kmh over that distance without reaching speeds of around 125kmh or 130kmh to make up for slow bends and other traffic.

If the elapsed time is only 30 seconds quicker at 14 minutes 30 seconds the average speed jumps to nearly 104kmh and you're busted but trucks can't do that.

Cover the distance 30 seconds slower in 15 minutes 30 seconds and the average drops back to just over 96kmh, meaning you're safe. Sixty seconds slower and the average drops to 94kmh.

But driving a modern car at normal highway speeds and after speeding up on divided road three or four times to pass slower vehicles or trucks while trying to keep your average on time to within a 30-second window would be like driving a stage in a timed car rally.

There's other point-to-point cameras on a 35km stretch between Bathurst and Blayney on the Mid Western Highway and another lot on the Mitchell Highway between Molong and Condumbul.

Sydney is about to get 25 new ones.

Seems a waste of money.

The Sydney co-ordinated adaptive traffic system called SCATS sets our traffic lights on a fixed-time basis where a series of signal timing plans are scheduled by the day of the week and time of day.

So in early mornings you can sit and wait at a red light with no other cars in sight in any direction while the lights go through their cycle.

Summer Street and Lords Place can be all over the place and if you're behind a truck or someone sitting there daydreaming when you get a green, you're lucky to get across before the lights change again.

The things apparently also go through a fixed cycle at Summer and Sale.

And the post office lights seem to be shonky, at night continually switching from green to red without any pedestrians or cars in sight.

It would be interesting to know just how much fuel Orange drivers waste while searching the city for a green light.

A little boy in Big W goes up to a checkout operator and says: "I've lost my Dad, can you help find him please?"

"What's he like?" says the operator.

"Beer and cricket," says the boy.