Smart transportation systems represent a transformative approach to managing urban mobility, leveraging advanced technologies to enhance efficiency, safety, and sustainability. Central to these systems are various types of sensors, which gather real-time data critical for informed decision-making. This chapter explores the diverse applications of sensors within smart transportation, categorizing them into traffic, environmental, vehicle, and infrastructure sensors. It delves into how these sensors are utilized for traffic management and control, public transportation optimization, autonomous and connected vehicle functionality, environmental monitoring, and smart infrastructure management. The integration of Internet of Things (IoT) technology and sophisticated communication protocols such as 5G and Dedicated Short-Range Communications (DSRC) underpins the seamless operation of these systems. Despite the promising advancements, challenges such as sensor accuracy, data security, and privacy concerns persist, necessitating ongoing research and development. Future trends point towards further integration of artificial intelligence and machine learning to enhance predictive capabilities and decision-making processes. Through detailed case studies and real-world implementations, this chapter illustrates the practical benefits and lessons learned from deploying sensor technologies in various urban settings. By synthesizing current research and technological innovations, it provides a comprehensive overview of the critical role sensors play in realizing the vision of smart transportation. The chapter concludes with an outlook on future developments, emphasizing the continuous evolution and potential of sensor applications to revolutionize urban mobility.