I think it depends on the city and its particulars. This was done in Galway in Ireland in the early 1990s where the downtown section was pedestrianised. The streets were narrow and traffic had always blocked up and cluttered the whole area. Closing it to traffic and pedestrianising it did wonders for making the downtown very sporty and trendy for business and culture and helped make the city a very popular place to live, work and visit.