Around the world, only eight cities have implemented a congestion charge as a way of helping ease gridlocked traffic, reduce transport-related carbon emissions and improve air quality.

With Aotearoa New Zealand having one of the highest rates of car ownership in the OECD, our two biggest cities - Tāmaki Makaurau Auckland and Te Whanganui-a-Tara Wellington - will likely be next in line.

Overseas experience shows that, implemented alongside other urban transport policies, congestion charging is a useful tool for reducing traffic and emissions. But it's important we make sure any congestion charging scheme doesn't disproportionately affect those already experiencing transport disadvantage.

In this report from WSP and the Helen Clark Foundation, Research Fellow Tom James recommends how any congestion charging policy implemented here can be made as fair as possible.

His report examines the potential equity impacts of congestion charging in Auckland and Wellington and sets out specific design considerations and principles that could be applied to any congestion charging scheme.

The report contains a range of recommendations for transport decision-makers, including:

• There should be key principles in legislation that any scheme must meet before being enacted,
• Robust community engagement is needed to gain support and combat misinformation,
• The design of the policy needs to consider those who have to come and go from the charging zone often, those who work irregular hours, and the unintended consequences on local streets,
• There should be a demonstration project or smaller initial rollout to build public confidence and monitor equity impacts,
• Exemptions should be limited to public transport, emergency vehicles, and those who provide mobility for disabled people,
• Other mitigation proposed by others or used in different jurisdictions can undermine the goals of the policy.