The Barr government Motor Accident Injury Bill passed in principle on Thursday, with the details to be debated when the Assembly resumes sitting next month.

But the ACT Law Society and ACT Bar Association have written to all parliamentarians highlighting fundamental problems with the proposed scheme.

Claimants will have choose between getting compensation for pyschological or physical injuries, meaning they cannot combine the physical and psychological injuries they suffer from the accident.

Their insurer only has to pay for one whole person impairment assessment as well, so if the injured person wants to be assessed for both physical and psychological injuries, they will have to foot the bill.

The definition of psychological injury also excludes psychiatric disorders such as depression and anxiety, meaning people can only get compensation for conditions like post-traumatic stress disorder or "mental shocks".

In a speech that drew heavily from the Law Society and Bar Association letter, Canberra Liberals leader Alistair Coe described the exclusions as "appalling".

"I cannot overstate the effect these changes would have," Mr Coe said.

"The government has not addressed the significant issues raised by stakeholders and the Assembly inquiry. The Canberra Liberals believe Canberrans should continue to have access to a comprehensive CTP scheme that supports the rights of motor vehicle accident victims."

The Law Society and Bar Association also said provisions that would allow children still getting treatment for their injuries four and a half years after their accident to pursue more benefits were easily circumvented.

"There is nothing to stop an insurer ceasing treatment and care after four years and five months and effectively avoiding the automatic consequences," they said.

However Chief Minister Andrew Barr said insurers could lose their licence if they did not follow the rules set out in the scheme which state they must provide people with reasonable access to treatment and care.

"Now of course there is no such thing as a perfect accident insurance scheme and as we've said from the start of this reform project, we're aiming to deliver a scheme that best reflects the prioirties and the values of this community," Mr Barr said.

"We have been upfront in acknowledging there will always be trade-offs and competing views when emarking on an overhaul this significant."

Mr Barr said of the 1500 people injured a year on Canberra's roads, only about 900 could access the existing, fault-based system.

"The changes we are making would mean around 600 more Canberrans would be covered," Mr Barr said.

However Mr Coe said this was only achieved by slashing the rights of not-at-fault drivers.

"Quality of life payments would be cut by 80 per cent. There'd be a 31 per cent reduction in loss of earning compensation, a 26 per cent decrease in care costs and reimbursement of private medical costs and public hosptial costs would drop 17 per cent and 6 per cent respectively," Mr Coe said.