Two of the 13 speed bumps or ''speed cushions'' will be removed from Flinders Way in Griffith after a review found they were not effective in reducing speed.

The modifications - which also include reducing others in size to improve bicycle safety - are expected to cost $50,000.

The speed cushions were installed on Flinders Way in May last year to help reduce traffic speeds and improve safety.

But a new survey shows only 22 per cent of respondents support the devices being there.

Territory and Municipal Services Minister Shane Rattenbury said since the installation of the devices, average speeds in sections of Flinders Way had decreased between 10 and 18 kilometres an hour, to be below 60km/h.

Traffic volumes had also decreased between 8 and 32 per cent ''without pushing the traffic volumes on identified alternative routes beyond their acceptable road limit''. That acceptable limit was 3000 vehicles a day for residential streets.

''Short term data indicates improved road safety with a decrease in the number of crashes when comparing the 10-month periods before and after the installation of the speed cushions,'' Mr Rattenbury said.

The government earlier this year sought community feedback on the effectiveness of the speed cushions. Roads ACT director Tony Gill said on Friday that 55 per cent of people surveyed felt they had reduced the speed of traffic on Flinders Way.

But 76 per cent of respondents believed the speed cushions had not improved safety on the road.

Problems identified included vehicles swerving to miss the road cushions and risking a head-on collision, cyclists frustrated by not having a clear way past them, and motorists parking their vehicles on top of the cushions. Some respondents also believed there were too many of the cushions.

Mr Gill said two sets of the cushions would be removed, one near Murray Crescent, the other near Hayes Crescent, because they had not proved to be effective.

Mr Rattenbury said there would also be changes to their size and spacing of the cushions. The distance between the devices and parked cars would also be modified to improve bicycle safety.

The work would be done this month.

Mr Rattenbury said the devices were initially installed in response to residents' complaints about speeding traffic.

''The results of the review show that the speed cushions have effectively achieved the desired outcomes by decreasing average speeds, increasing road safety and decreasing traffic,'' he said.