Acting Sergeant Dave Stevenson of Knox highway patrol said the woman recorded a blood alcohol reading of 0.205 and lost her licence on the spot.

Operation Driftnet targeted drink-drivers around licensed premises in Rowville and Bayswater in the evening and early morning of January 27-28. Police breath-tested 272 drivers and 11 were found driving over 0.05.

The operation also caught 30 drivers for offences including overloading, not wearing seatbelts, having an unregistered or unroadworthy vehicle or being unlicensed.

Acting Sergeant Stevenson said this worked out to "around one car in 25 doing the wrong thing".

A P-plate driver had his car impounded after he was caught driving 106km/h in a 60km/h zone with passengers. Acting Sergeant Stevenson said the man's vehicle was impounded for 30 days.

A similar operation in Bayswater last Thursday night breath-tested about 45 drivers. Ten were issued with penalty notices for various offences including driving while unlicensed and speeding.

Acting Sergeant Stevenson said two drivers were caught driving with false number plates and another man would face court for driving while disqualified.

He said the high number of drivers caught breaking the law was concerning. "We caught one in 25 people [on January 27-28] doing the wrong thing. Imagine how quickly you pass 25 cars on a highway and one of them is doing the wrong thing - it's a lot."

He said highway patrol and uniform police would continue to target drink-drivers throughout Knox in February.