As one of the essential parts of the smart city concept, the realization of intelligent transportation has become a trendy topic, and one of the fundamental ways to realize intelligent transportation is to introduce intelligent street lights. This paper mainly presents a design of a rear-mountable intelligent street light which can be installed on light posts easily. On one hand, based on the original street lights, it can fulfill all the functions of a street light after installation without the costs of replacing existing street lights. On the other hand, our approach can eliminate a lot of disassembly and installation procedures, which typically involve many engineering costs. On top of the functions provided by traditional street lights, we propose to include a AI-supported camera for traffic and parking monitoring, a full-coverage Wi-Fi access point, a laser sensor for intelligent monitoring of pedestrians crossing the road, and an electric car charging point. The co-development of the companion app can operate selected functions, for example, parking reservation and electric car charging, of the intelligent street lights. This proposal has been tested in a controlled lab environment which shows the feasibility of hardware selection, welding approaches, and the companion app design. Our future work aims to test our proposal against real-world environments and actual road conditions.