In suburban areas, traffic issues are generally related to elevated speeds and volumes and a perceived reduction in personal safety. In response, traffic engineers have designed and implemented a variety of traffic calming measures for local and collector streets, with significant speed reductions and other benefits. Less common are measures to address traffic issues on arterials which (if implemented) might reduce speeds, thereby encouraging more sustainable transportation modes and lessening automobile dependence. A geographic information system (GIS) based tool has been developed to provide decision support for the development of neighbourhood traffic calming plans for all street types. This tool is potentially useful because of the increased use of traffic calming measures and the growing public desire for safer streets. Decision support (provided by the tool) is dependent upon measured or perceived problems, roadway type, and user objectives, as well as the potential impacts and current installation costs of traffic calming measures. An application to suburban Hamilton demonstrates the functionality of this tool.Key words: traffic calming, suburban retrofitting, urban sustainability, decision support system.