WA’S controversial breath-testing system, which favours drink-drivers, will be scrapped under new “What You Blow Is What You Go” laws set for State Parliament next year.

Police Minister Michelle Roberts has vowed to get rid of the RBT loophole, saying it was time WA joined the rest of Australia and eliminated a back-calculation process that potentially reduced a drink-driver’s blood alcohol content (BAC), meaning a lesser penalty or, in some cases, allowing offenders to get off.

The move follows a Monash-Curtin University study in 2014 that slammed the current method of testing drink drivers in WA, saying back-calculation was “found to favour drink drivers and therefore should be ceased”.

“We should have accepted best practice, which is used right around Australia now,” Mrs Roberts said. “WA is the only State that is lagging behind. This is a discredited and outmoded way of calculating it.

“The fairest and best way should be that whatever people blow, that should be what they are charged with. My view is no tolerance to drink drivers.”

Under the current method, WA drivers are stopped by police and given a preliminary roadside breath test.

A further evidentiary test is then done at a booze bus or police station if drivers initially blow over the legal limit of 0.05.

Camera Icon WA’S controversial breath-testing system, which favours drink-drivers, will be scrapped under new “What You Blow Is What You Go” laws set for State Parliament next year. Credit: Lincoln Baker

But WA is the only State in Australia that back-calculates blood alcohol levels from evidentiary tests. The method is based on the premise a driver’s BAC will be on the rise when stopped for a roadside breath test and the evidentiary test reading will be higher than the actual alcohol level when motorists were driving.

To account for this presumed increase, evidentiary BAC readings are back-calculated to the driver’s “time of last drink”.

“These back-calculations are based on the formula that a BAC rises at 0.016g/100ml per hour for two hours and then falls at the rate of 0.016g/100ml per hour,” the 2014 study says.

“If a driver can prove (convincingly) that they recall their time of last drink then that is the time used in the calculations.”

The study found that of 118 drivers initially detected with an illegal BAC level over six weeks, 26 were let off the hook because of the back-calculation method. Another 65 drivers received a reduced charge.

“The back-calculation is just a way for some people to get off the hook or think that they have a way of getting off the hook,” Mrs Roberts said. “It is very difficult to ascertain if they are telling the truth.”

Mrs Roberts said she had the blessing of acting Road Safety Commissioner Iain Cameron.

Discussions with police had commenced and she hoped to “have the law changed in the first half of next year”.

Mrs Roberts said police would be “drink testing and drug testing” over Christmas:

“Think about your fellow human beings and the injury to a child or someone else’s loved one if you drink and drive”.