Thousands of drunk drivers who are eligible, are not getting an alcohol interlock sentence - and even if they did, they might get away with never having the device fitted to their vehicle.
Once the interlock device is fitted, the driver must breathe into it and if alcohol is detected, the vehicle will not start.
In the 2020/2021 year 4138 people received an alcohol interlock sentence, but the Automobile Association's (AA) research shows this is only about half of total number who were eligible for one, under laws that changed in 2018.
In addition, only two-thirds of those sentenced actually go on to install the device in their vehicles.
AA road safety spokesperson Dylan Thomsen said the figures were concerning.
"[It] really matters because what the figures show is for each interlock we put into a car, that prevents about 100 attempts by somebody with alcohol in their system to drive, a year.
"So interlocks are hugely effective at keeping drunk drivers off our roads."
"The biggest issue that we have with interlocks right now is that a large number of the people who are sentenced to them aren't actually getting them installed in their car and the reason for that is because there's no follow up in the system.
He said it could be easily fixed if interlock providers and authorities worked together.
"There's two companies that are interlock providers so you have to go and get it installed by one of those registered suppliers. Then people have to go back monthly to have data downloaded from the device and for it to be tested and checked. So there's great information there but we don't have good communication going on between the authorities."
"We need those two parts of the system talking to each other."
In July 2018, the Land Transport Act was amended to make alcohol interlock sentences mandatory for anyone convicted of two or more drink-driving offences within a five-year period.
The sentence also became mandatory for anyone convicted of driving with alcohol in their system that exceeded a certain threshold (800 micrograms per litre of breath or 160 milligrams per 100 millilitres of blood, which is over three times the legal limit).
Thomsen said it would be helpful if the courts collected data on why someone who was eligible, did not get sentenced.
Ministry of Justice policy manager Oliver Sanders said the law provided a number of reasons why a person might be exempt from the sentence, including medical reasons, not having a driver's licence or a car, or living in an area where an interlock provider was unavailable.
Analysis conducted by the ministry in 2019 found that the use of interlocks varied regionally. For instance, in Te Tai Tokerau 38 percent of eligible offenders were sentenced to an alcohol interlock, while in Taranaki/Whanganui that rate was 69 percent.
