But the Department of Transport and Main Roads has defended the proposal to expand the existing security camera regime, saying audio recordings would help criminal courts assess the events leading up to assaults on drivers or passengers.

The department says the element of workplace risk for taxi drivers is very high as they work alone and might pick up a group of drunken revellers late at night and then suffer an attack.

Queenslanders are being asked for their opinions on the taxi audio-capture plans, which were first floated by the Bligh government last year.

In a new issues paper designed to spark public comment, the department suggests in-cab security cameras would capture and store video and audio on a 72-hour loop.

Queensland Privacy Commissioner Lemm Ex argues expanding the video recording scheme to include audio takes the collection of personal information in taxis "to a whole new level".

Mr Ex argues the government has provided little information to justify the expansion and the only guarantee information can be secured from abuse and misuse is not to store it in the first place.

Compared with video, audio allows the capture of personal information that is "potentially limitless both in breadth and sensitivity".

Mr Ex argues people will have to endure having their conversations recorded or avoid using taxi services altogether.

The commissioner notes passengers may have conversations with the taxi driver, other passengers or to a person over the phone on topics such as health details, business information, political opinions, philosophical beliefs and "intensely private information such as sexual preference or practices".

"The biggest concern is who can access the record and for what reasons," Mr Ex says.

The commissioner says the information paper outlines clear checks and balances surrounding offences committed in taxis, but restrictions on third party use of the audio record are unclear.

"Audio records of conversations in taxis are in effect a 'wire-tapping library' which will be a far more valuable resource for the [Queensland Police Service] than the current video record," Mr Ex says.

Current legislation for "authorised purpose" for accessing cab video recordings includes the open-ended criterion of "another purpose relating to a police officer's performance of duties as a police officer".

"Accordingly, this proposal that would give QPS carte blanche freedom to eavesdrop on the Queensland community without any accountability mechanisms is, from a privacy perspective, both alarming and disturbing," Mr Ex says.

But the Department of Transport and Main Roads mounts a strong defence in the issues paper, saying the QPS would have no new level of access to recordings from taxi security cameras because of the addition of audio.

"The concept of a 'wire tapping library' is not realistic in that QPS are required to have an understanding that a targeted subject has travelled in a specific taxi, become in contact with that taxi within 72 hours and additionally have a justified purpose for downloading recordings," the department says.

It points to a case that went before the Court of Appeal where audio would have come in handy.

The department says a 28-year-old taxi driver was charged with two counts of indecent treatment of a child under 16. The child was 14 at the time and the matter is currently awaiting a retrial.

"In summary, the footage from the approved taxi security camera system could not verify or disprove the allegations or the truthfulness of statements made by the complainant or the appellant," the department says.

The department outlines a range of crimes where audio and video footage "could be invaluable to determining the offence".

In cases of rape, attempted rape and sexual assault, audio would give a clearer indication on whether the victim gave consent and if they had the capacity to give consent.

In assault cases, audio would confirm whether there was prior provocation or verbal argument.

Sound recordings could also confirm whether a verbal threat was made.

The department says taxi drivers' work environment "can be dangerous and confronting" and there is a risk of a passenger stabbing them to death.

"This may seem like an extreme example; however, these types of incidents unfortunately happen as evidenced by the tragic death of a Melbourne taxi driver earlier this month," it says.

The department says the recording of audio with images is already prevalent in many buses fitted with CCTV systems in Queensland.

It says security cameras do not necessarily stop crime but their presence can deter it and enhance safety perceptions.

"In 2011, there were more than 217 downloads made from taxi security cameras as a result of an assault against a taxi driver. That equates to more than one physical assault every second day.

"For the same period, 199 downloads were made from taxi security cameras as a result of a police investigation."

The department says under the proposal, the encrypted data will be automatically wiped after 72 hours unless downloaded for an authorised purpose.

Under current laws, video is only retained for 32 hours before being wiped.

If the plans are implemented, stickers inside and outside the taxi would inform passengers about the audio recording.

"While it is acknowledged that taxis are sometimes treated similar to a confession booth, they are public passenger vehicles and the inclusion of audio recording is proposed primarily in the interests of passenger and driver safety," the department says.

The department says taxi booking companies and the QPS are the only ones currently in possession of the software to download taxi recordings.

The department is notified within one working day and conducts audits to ensure the law is being followed.

Transport Minister Scott Emerson said audio was recorded in taxis in Western Australia and in South Australia in emergency situations.

"While the use of audio recordings will further improve driver and passenger safety and complement video recordings, it's important that we consider feedback from passengers and drivers," he said in a statement.

Mr Emerson, who raised privacy concerns when he was in opposition, had previously been tight-lipped about whether the Newman government would push ahead with the plans.

When Fairfax Media asked him about the issue six months ago, Mr Emerson did not respond directly to questions about his stance, but said he would properly consider privacy issues.

“I've asked that this proposal be considered by the Privacy Commissioner and their feedback incorporated in the department's policy paper when it's presented to me," he said in May.

The idea of recording audio in cabs was recommended in a security camera discussion paper released by the Department of Transport and Main Roads under the Bligh government last year.

In May, Mr Ex, the then-Acting Queensland Privacy Commissioner, told Fairfax Media such proposals always had pros and cons and it was crucial people were made “well aware” before the journey began that audio recording would be undertaken.

“There might be such things as two people from an organisation who might be discussing commercial-in-confidence material or it might be office gossip so people should be aware that any discussion they might have will be recorded,” he said, calling for adequate signage if the proposal was adopted.

The second concern was how the material would be stored and accessed.

“These were covered off to a large degree in the previous discussion paper so I would anticipate that those similar issues would be addressed on any new proposal going forward,” he said at the time.