A test run for the lengthy load was carried out on State Highway 73 earlier this week.

Delays are expected on a main highway between Canterbury and the West Coast as oversized trucks move materials for a major bridge project.

From Monday, trucks will begin moving 45-metre loads from Hornby, in Christchurch, to the new Taramakau Bridge project, between Greymouth and Kumara Junction.

The trucks will be carrying steel bridge beams measuring up to 34m.

The NZ Transport Agency (NZTA) said the 44 beams needed at the Taramakau River site would be transported via State Highway 73 (Arthur's Pass) over the next three months.

READ MORE: Work to replace New Zealand's last rail-road bridge begins

One load is scheduled to leave Christchurch at 4.30am up to three times a week, arriving at Taramakau about 6pm.

Motorists are advised to expect minor delays due to the length of the load and the slow and winding nature of parts of the highway.

More significant delays of up to 20 minutes can be expected in the Porter's Pass and Otira Viaduct areas.

It is expected the load will be between Springfield and Arthur's Pass from 7.30am to 12.30pm and between Arthur's Pass and Otira about 2.30pm during each trip.

"The Transport Agency thanks all drivers heading to the West Coast on a day the long load is scheduled for being patient if they are slightly delayed," NZTA said in a statement.

The $25.8 million Taramakau Bridge project, on State Highway 6, involves building a new two-lane bridge downstream of the existing one-lane road and rail bridge. A section of SH6 will be realigned and an overpass built to take traffic over the railway line, and an off-road cycle and pedestrian link will also be built.

Motorists can visit the NZTA website – nzta.govt.nz/traffic – on the day they are travelling to see if a truck is scheduled.