It's one of the fastest ways to ruin your day. Flashing lights fill the rear view mirror, an icy feeling pierces your chest and that mixture of guilt, frustration and anger curdles as the officer strides toward your door.
There is plenty of conjecture surrounding speed in Australia. The government will tell you speed is a killer and that you are risking life and limb by travelling a few kilometres per hour more than its limits.
You may have heard it all before - the police are out to get you, they need to fill their quotas and keep state accounts running smoothly. Their equipment is infallible, you can't fight fines and a clean record will do nothing for you if the radar says you've done the wrong thing.
The myths, misconceptions and old wives' tales surrounding speed are numerous. We spoke with authorities, consulted police equipment manuals and talked to speed experts in order to break down myths and reinforce 10 truths you can take to the bank.
Police radar and laser equipment does not work over the horizon
It's an old common spot of advice that motorists crossing the red centre may hear – "be careful on the road, police can book you several kilometres away, you won't even see them".
That's not true as police speed detection equipment needs a direct, uninterrupted line of sight to its target. Special military radars can look over the horizon, but they are not used to keep track of speeding motorists.
Speed guns don't work well in the rain
Speed detection equipment works by sending a series of signals from a device, bouncing that signal off a target vehicle, and measuring the distance it travels in a set time.
Poor weather can affect the accuracy of radar and laser-based speed detection equipment.
Operating guidelines for the Stalker brand of speed gun say "Rain absorbs and scatters the LIDAR signal. This reduces the range and increases the possibility of obtaining readings from the speed of the raindrops".
The operator's manual for another common brand of speed gun says "visibility conditions also affect the performance of the ProLaser III ... atmospheric or climatic conditions that impair vision also adversely affect the operation".
A Victoria Police spokesman told Drive "certain weather conditions may have an impact on the speed detector's effective operational range".
"Operators trained to use speed detectors are instructed on the impact of weather and can identify adverse effects caused by weather conditions," he says.
Speed detection equipment is always accurate
Speed guns must be calibrated to standards monitored by the National Association of Testing Authorities. Victorian police calibrate speed guns annually to make sure they meet legislative requirements.
NSW police say "all speed measuring devices comply with Australian and national standards", but as with most states they do not publish acceptable margins for error.
Victorian legislation states analogue roadside speed cameras must have a margin for error of less than 3km/h or 3 per cent of a given speed, which drops to 2 per cent or 2km/h for digital devices, such as handheld laser speed guns.
While police equipment must be accurate, operational errors can have a negative effect for motorists. An instruction manual for one type of speed device says failing to hold the laser gun steady can exacerbate readings, and that a twitch that moves the laser beam from a car's grille to the passenger compartment can increase speed readings by more than 10km/h.
Speeding fines consultant Scott Cooper says it is easy for police to fine the wrong car at long distances.
"Any tremor of the human hand will make this thing cover half a football field – in multiple vehicle situations, [police] will not know which vehicle returned a reading," he says.
"There is nothing that device can do in court to prove when, where or what vehicle that came from."
Equipment can dob in the wrong car
Cooper says police equipment is not as accurate as people expect it to be.
"Everyone expects when they hear the word 'laser' that this thing is firing a pinpoint, thin red beam at massive distances. I'm here to tell you it does not," he says.
"It fires a beam that spreads out like a torch, and at 300 metres the beam width on a ProLaser III is 1.2 metres, that's a massive circle."
An operator's manual for the Stalker speed measurement laser says police need to be careful when booking motorists in traffic.
It says that over distance, "the beam becomes wide enough that some separation between targets is necessary to insure accurate target identification".
"The beam does get proportionally wider as distances increase. It is suggested, in heavy traffic and multi-lane usage, that speeds be obtained at the shorter distances to assure proper target identification."
Drivers can ask to see evidence used against them
Police are not always required to show exactly what their equipment has recorded, but may do so to demonstrate why a motorist has been stopped.
When speeding motorists are caught in NSW, drivers can later visit a police station and view footage of the incident.
Victoria police say "motorists are entitled to ask for a speed readout and officers are encouraged to invite drivers to inspect the speed reading, but they are not legally required to do so before issuing a ticket".
Highway patrol do not operate on a quota system
Some police agencies deny there is a quota system compelling officers to book a set number of people each month.
But Australian governments budget on receiving about $2 billion in traffic fines each year, money that is relied upon by state treasuries.
NSW Police did not address Drive's question asking whether quotas are in place, while a Victoria Police spokesman insists quotas are not used.
"Quotas for vehicle stops are a common misconception, there are no and never have been quotas in place for the highway patrol," he says.
"Motorists can be stopped anywhere, at any time, by any member of Victoria Police and be asked to do a breath test and licence check."
An Adelaide newspaper recently published a police email exchange that hinted at a quota arrangement.
"We fell below our expected returns for traffic contacts for the last reporting period," an email said.
"We'll hammer those poor people who choose to drive when we're night shift."
South Australian Police Commissioner Gary Burns responded by saying "there are no quotas", but there were benchmarks for the minimum number of people police should interact with.
"However, I, and the executive, make no secret of the fact that we have broad road safety benchmarks. These are not quotas.
"The most important issue is that a driver who has done the wrong thing is spoken to and dealt with in some manner - documented caution, [traffic infringement notice], report or arrest."
Radar detectors can help avoid trouble
In all states except Western Australia, radar detectors are more likely to get you into trouble than out of it.
Radar detectors are illegal to use in all states and territories except WA. Many police patrol cars are equipped with sensors that seek out radar detectors or jammers, helping police to find and confiscate illegal equipment.
A small number of businesses in WA sell anti-radar devices, with one website promising its equipment is "100 per cent undetectable by all police radar detectors".
A radar detector salesman who preferred not to be named would not say how many units are shipped to eastern states, and that once units were received by customers, "what the individual does is up to the individual".
It may be possible to effectively use radar detectors east of the Nullarbor, but drivers risk losing their licence and paying thousands in fines if caught doing so.
Demerit points apply if you are booked interstate
Improved communication between state road and police authorities means that fines accrued while travelling within Australia follow drivers to their home state. If a Victorian driver is caught speeding in the Northern Territory, they pay a fine to the NT government, but demerit points are applied by the state that issues their licence.
Police can let me off with a warning
Victoria Police policy is that officers "are able to exercise discretion for breaches of a minor nature".
South Australian Police Commissioner Gary Burns says police will "always maintain the ability to apply discretion".
NSW police may be less friendly. A spokeswoman for the force says an average of more than 575 people were booked for speeding every day in July, and "those that continue to risk their own lives and those of other road users when speeding will most certainly be identified and prosecuted".
Good behaviour could get you out of trouble
In some circumstances, a proven record as a safe driver can help motorists to escape conviction for minor offences.
Victorian drivers can apply for an internal review of their alleged offence and may have fines replaced with an official warning. Drivers who are booked by multiple speed cameras in a short period, or receive a rash of fines in the mail without an adequate chance to modify their behaviour, can apply to have fines withdrawn.
Other speeding offences may require that drivers have not been issued with a traffic infringement or official warning for the past two or three years, and that they do not deny committing the offence.
NSW motorists can challenge traffic fines in court. Even if the motorist is found guilty, magistrates may apply a "section 10" legal bond, which does not record a fine, conviction or any other form of punishment against the driver. Motorists cannot apply for more than one section 10 bond during any five-year period.
Drivers who run out of demerit points in NSW can also elect to be of good behaviour for 12 months, on the proviso that accruing a further two demerit points will see their driving ban doubled.
As with NSW, South Australian and Queensland drivers who exceed the maximum permissible number of demerit points can swap a suspension for a period of good behaviour as long as they do not acquire more than a set number of demerit points over the course of a year.