Compulsory third party (CTP) insurance premiums in the Australian Capital Territory have risen for the second time this year.

From this weekend, Canberrans will pay $448.60 in CTP for a private car. The rate had already increased to $416 in March from $385 last October.

The ACT Department of Treasury says CTP premiums charged by NRMA Insurance will increase by an average of 7.8%.

"This increase is due to the collapse in investment markets as a result of the global financial crisis which means that insurers will achieve lower investment returns," the department said.