Perth's notoriously bad mergers have been guided down the right path, with the WA government's freeway merge lines improving traffic flow and cutting journey times.

Average travel speeds have increased by nine per cent on Kwinana Freeway northbound, by 28 per cent on Stock Road, by 31 per cent on Orrong Road and by 22 per cent on Great Eastern Highway.

"Installation of merge lines across the freeway network has noticeably improved journey times, and the state government is also planning an educational campaign to assist drivers to merge safely," WA Transport Minister Bill Marmion said on Thursday.

Mr Marmion said merge lines would be rolled out on the Reid, Roe, Tonkin and Leach highways.

He said the traffic signal timing project had also reduced congestion for road users and would be expanded to cover all 400 sets of traffic lights on the metropolitan road network.