Canterbury motorists are being urged to drive to the conditions as winter maintenance and planned works continue across the region’s state highway network.

NZ Transport Agency said while the summer construction season had finished, crews were still carrying out essential winter maintenance and responding to emergency works when needed.

With school holidays about to get underway, drivers travelling around the South Island are likely to encounter winter conditions, particularly on inland routes and at higher elevations.

NZTA said ice could form quickly when temperatures drop, especially on bridges, in shaded areas, and where moisture has refrozen. Black ice can be difficult to see, while frost, freezing fog and snow can reduce visibility and grip.

Drivers are being advised to slow down, increase following distances, avoid sudden braking or steering, and check road and weather conditions before travelling.

NZTA said even treated roads could still have ice or loose grit on the surface, and conditions could change throughout the day.

Crews are using a mix of grit and calcium magnesium acetate, known as CMA, to manage ice and snow. Grit helps improve tyre grip when ice has already formed, while CMA lowers the freezing point of water and is often applied before frost is expected.

NZTA said CMA was most effective when used ahead of a frost event, particularly on bridges, shaded areas, river flats and inland valleys where cold air settles.

A number of planned works are also underway or scheduled across Canterbury.

On SH1 at the Kaiapoi Bridge, a temporary 80 km/h speed limit is in place over the Kaiapoi River until Thursday 9 July. NZTA said the reduced speed limit was needed to protect concrete pours being used to strengthen the bridge. The work is being carried out underneath the highway and is expected to continue until mid-July.

On SH1 at Dunns Crossing and Walkers Roads, finishing works are continuing after the roundabout and subway opened. A 70 km/h speed limit will remain until final skid-resistant surfacing and line marking are completed in October, weather permitting.

Night works will take place on Sunday 5 and Monday 6 July from 7pm to 5am to complete road shoulder construction on the eastern approach. During that time, the highway will operate under one lane with temporary traffic lights through the roundabout.

In Timaru, work is continuing at the SH1, Grants Road and Showgrounds Shopping Centre intersection. Crews are working weekdays from 7am to 7pm, with SH1 reduced to one lane in each direction and a 30 km/h temporary speed limit in place.

For the next month, access to the Showgrounds Shopping Centre will be from Bridge Road, with the usual exit via Grants Road remaining open.

The Lyttelton Tunnel will also close overnight for essential deluge compliance testing on 15, 16 and 17 July. Closures will take place from 10pm to 5am, with short closures between 10pm and 11pm for preliminary testing. From 11pm, full 50-minute closures will be in place, with both lanes reopening on the hour to clear traffic. Normal operations will resume at 5am each day.

On SH82, work to replace the Waihao North River Bridge is continuing. A single-lane temporary bridge is in place, controlled by temporary traffic lights, with a 30 km/h speed limit applying.

NZTA said the new Elephant Hill Stream Bridge is now open. The bridge has been upgraded to two lanes and has no load restrictions.

Motorists are reminded that other less disruptive state highway works may also be taking place, and all work is weather dependent. Drivers are encouraged to check Journey Planner before travelling.