Concerns over air pollution in the city centre means Cardiff will hold its first car-free day on Thursday.
But only Park Place in Cathays will be closed to all traffic until 00:00 BST on Friday.
It will become a street market and host a transport exhibition giving information on sustainable travel.
While all commuters will be encouraged to leave their cars at home in a move designed to combat air pollution, no other areas will be closed off.
Jane Lorimer, director of cycle charity Sustrans Cymru said it was a “positive first step”.
Councillors backed plans to ban cars in the city centre for one day each year, to cut air pollution, last October.
But cabinet member Ramesh Patel said it would be “grossly irresponsible” to widen the area before the first plan had been reviewed.
He added: “With the new bus interchange developing, a cycling strategy being produced, planned investment in our railways and future plans for the metro, sustainable transport is a major priority for the council.
“Making walking, cycling and public transport more attractive and viable options for commuters and residents are integral to Cardiff’s continued development and achieving our aspiration to become Europe’s most liveable capital city.”
Car-free days already take place in Delhi, Paris and London.
It is claimed air pollution is linked to tens of thousands of deaths in the UK annually.