The most useful periodical for public art issues is the quarterly Public Art Review. Often issues are devoted to specific topics. Articles tend to be more relevant to programs and projects that are well established. Check out their web site (www.forecastart.org) for more details and for artist opportunity listings.
From time to time articles on public art topics will be published in contemporary art journals such as Art in America, but they tend to be about national or international issues, artists, or controversies and rarely about small-scale projects or programs. Sculpture magazine (published by the International Sculpture Center, 1050 Potomac Street NW, Washington, DC 20007) is a good resource for sculptors; often it lists public art opportunities and recently installed works throughout the country. In the past they have published special issues devoted just to public art.