After years of post-earthquake delays, Curletts Rd between Blenheim Road and Main South Road has been expanded into a four-lane carriageway with clearways to ease congestion.

One of Christchurch's most congested streets has been cleared as part of plans to improve traffic flow.

After four years of motorists having to manoeuvre through traffic cones on Curletts Rd, a $1.8 million project to transform the 800-metre section between Blenheim Rd and Main South Rd into a four-lane carriageway is complete.

The New Zealand Transport Agency estimated traffic volumes on Curletts Rd increased by 30 per cent in the aftermath of the earthquakes because of businesses relocating to the west of the city.

Clearways are in force from 7am to 9am and 3.30pm-6pm on weekdays – peak travel times along a key commuter and freight route that used to be one lane in either direction.

Traffic islands and median strips are also features of the revamp that started in January.

Pedestrians and cyclists are able to access properties on Curletts Rd through a shared pathway.

Riccarton High School deputy principal Shane Morrow was relieved the roadworks had been completed.

"We're happy it's all over and we look forward to improved access for our students and their families."

He did not expect the morning clearway to be an issue for parents.

"The clearway has only just come in though most of our parents would drop the students off into Vicki St, the Main South Rd entrance anyway," he said.

The clearway has provided an obstacle for Sarah and Wing Mo , who have owned the Curletts Road Dairy for 12 years.

Wing Mo said takings had dropped 50 per cent since the work started and doubted there would be an upswing because the clearway and newly-installed yellow lines outside the premises would deter potential customers.

"It's very bad for my business. People could get parking here easily and find something quick and go," he said.

"I've lost many customers."