The Western Cape will not build any new major roads for the next four years, Premier Helen Zille said on Wednesday.

Funds earmarked for new roads would instead be invested in public transport, she told a Cape Town summit of leaders of regional governments from several continents.

Reducing dependence on private vehicle travel was essential for reducing the traffic congestion that hampered productivity and polluted the air.

"The days of one person travelling to work by themselves in a car are numbered. It is simply unsustainable."

Rather than introduce "sticks", the province wanted to offer people "carrots" - incentives to change behaviour.

"This is why our policy in the Western Cape is designed primarily to upgrade our transport infrastructure to make it more convenient, cheaper and reliable," she said.

"The response to reduce congestion in the past was to build more lanes and roads. But international experience has shown that building new roads and adding new lanes simply encourages more cars."