Up to 1.25m is being added to the width of the narrowest parts of Dyers Pass Rd, which is only about 5.5m to 6m wide in many areas.
Higgins Construction is working on behalf of Christchurch City Council to increase the width of the road to a consistent 6.75m.
"The additional road shoulder width is expected to improve everyone’s safety and reduce conflict between road users," said council acting head of transport Lynette Ellis.
The road widening work is part of a $7.2 million project to improve the safety of the road, which has a high crash rate.
"The steep terrain means that when crashes do happen they often result in severe injuries, so in addition to widening the road, we are installing guardrails in high-risk locations.
"This should reduce the severity of crashes that do occur where vehicles would have left the road," Ellis said.
Three kilometres of guardrail is being put in.
Waka Kotahi NZ Transport Agency is meeting about three-quarters of the cost of the of safety improvements as part of its Safer Networks Programme.
The safety improvements are due to be completed by the end of August.
