From this article, it looks like pedestrian malls are an important piece, but they can't do all of the heavy lifting on their own. There has to be adequate dens

From this article, it looks like pedestrian malls are an important piece, but they can't do all of the heavy lifting on their own. There has to be adequate density and multiple purposes so people are organically there at different times of the day to create a sense of safety. This is addressed extensively in The Death and Life of Great American Cities.