Wireless sensor networks (WSN) are a target technology for intelligent transport systems (ITS) because they offer benefits of low-cost, simple installation and ease of deployment. In order for WSN to achieve trademark performance in traffic monitoring, and compete effectively with present day traffic surveillance systems, certain design requirements must be met. In this study, the authors identify vital design issues that must be considered to facilitate deployment of WSN for traffic monitoring. The authors classify these design issues into four different categories namely, sensing modality, power conservation, network reliability and security. The authors conduct their investigation via extensive study of the recent literature and comprehensive survey of existing WSN-based ITS technologies. The authors conclude each discussion by presenting open research issues. The authors then discuss two promising application areas for traffic monitoring WSN namely, active traffic management and integrated traffic management.