The application and research of wireless sensors have received increasing attention. This paper details the application of wireless sensors in intelligent transportation systems (ITS), and discusses the design of wireless sensor networks based on typical applications within ITS. With technological development and maturity, wireless sensor network technology can be applied in more critical scenarios within ITS, such as electronic toll collection, traffic safety and autonomous driving, parking management, and traffic guidance systems, further promoting the development of ITS. Wireless Sensor Networks Promote the Development of Intelligent Transportation Intelligent Transportation Systems (ITS) in urban transportation are mainly reflected in micro-level traffic information collection, traffic control, and guidance. They improve the efficiency of the transportation system by enhancing the effective use and management of traffic information. ITS primarily consists of subsystems such as information collection input, strategy control, output execution, and data transmission and communication between subsystems. The information collection subsystem collects vehicle and road information through sensors. The strategy control subsystem calculates the optimal solution based on set objectives (such as maximizing traffic volume or minimizing average waiting time) using computational methods (such as fuzzy control and genetic algorithms), and outputs control signals to the execution subsystem (generally a traffic signal controller) to guide and control vehicle traffic to achieve the preset objectives. Wireless sensor networks (WSNs) are a new technology that integrates short-range wireless communication, microelectronic sensors, and embedded systems, and are increasingly being used in fields requiring data acquisition and detection, such as intelligent transportation systems. Based on the IEEE 802.15.4 standard, ZigBee technology possesses the following advantages: ① Low power consumption: two standard AA batteries can support one node for 6-24 months; ② Strong networking capability: networks can support up to [number] nodes and various networking methods such as tree, star, and mesh; ③ Long transmission distance: outdoor transmission distance between two nodes can reach hundreds of meters, and can reach several kilometers with increased transmission power; ④ High reliability: multi-level security modes are available; ⑤ Low cost: an open and simplified ZigBee protocol stack operates in the license-free 2.4GHz ISM band. WSNs offer excellent characteristics and provide an effective means of information acquisition for intelligent transportation systems. They can monitor vehicles in all directions at intersections, and based on the monitoring results, improve and simplify signal control algorithms to increase traffic efficiency. WSNs can be applied to control and guidance subsystems within execution subsystems. For example, this technology can be used to improve signal controllers and implement bus priority functions in intelligent public transportation systems. Construction of Wireless Sensor Networks for ITS As shown in Figure 1, in the wireless sensor network structure, aggregation nodes installed along both sides of the road form a self-organizing multi-hop mesh basic network architecture. Dedicated sensor terminal nodes for traffic information collection communicate with each nearby aggregation node in a star network. The final data is aggregated to the gateway node. The gateway node can be installed as a module within the traffic signal controller at an intersection, transmitting the collected data to the traffic management center for further processing via the signal controller's dedicated network. In the deployment of the wireless sensor network, aggregation nodes can be installed on roadside pillars, crossbars, and other traffic facilities. The gateway node can be integrated into the traffic signal controller at the intersection. Dedicated sensor terminal nodes can be buried under the road surface or installed along the roadside. Moving vehicles on the road can also dynamically join the sensor network by installing sensor nodes. The wireless sensor network structure uses wireless sensor networks for traffic information collection . In traffic information collection, terminal nodes can use non-contact geomagnetic sensors to periodically collect and sense information such as vehicle speed and distance within the area. When a vehicle enters the sensor's monitoring range, the terminal node collects important information such as the vehicle's speed using a magnetic sensor and transmits this information to the next node that wakes up at a set time. When the next node senses the vehicle, it estimates the vehicle's average speed by combining the estimated travel time between the two sensor nodes. Multiple terminal nodes collect and process their information, which is then aggregated at the gateway node via a convergence node for data fusion. This process yields information such as road traffic flow and vehicle speed, providing accurate input information for intersection traffic signal control. By installing various sensors such as temperature, humidity, illuminance, and gas detectors on the terminal nodes, it is also possible to detect road conditions, visibility, and vehicle exhaust pollution. [align=center]Deployment of Wireless Sensor Networks for Traffic Information Collection[/align] Application of Wireless Sensor Networks in ITS Implementing the bus priority function in an intelligent public transportation system requires modifying existing traffic signal controllers. By adding auxiliary equipment such as sensors, traffic signal controllers can estimate the arrival time (travel time) of buses at intersections, calculate whether buses need priority at intersections (passenger numbers can be selected as the priority weight), and then select an appropriate priority control strategy, prioritizing buses by adjusting the green light ratio. The modification of the traffic signal controller includes: ① onboard wireless communication terminal nodes; ② integration of a wireless gateway on the intersection traffic signal controller; ③ terminal nodes for bus positioning; ④ the above functions can be achieved by constructing a ZigBee-based wireless sensor network. When approaching an intersection, the onboard ZigBee wireless terminal node broadcasts bus information. After the roadside wireless sensor network acquires the information, the bus positioning terminal node tracks and collects the information, which is then aggregated to the wireless sensor network gateway node. Finally, the information is transmitted to the traffic signal controller through internal connections for appropriate priority processing. Network Node and Gateway Node Design: In the design of the ITS wireless sensor network, network nodes need to be designed separately according to their functions. The software functions of the terminal node, aggregation node, and gateway node are shown in Figure 3. Terminal nodes are equipped with various sensors for collecting information on moving vehicles and acquiring road information. Their functionality can be implemented according to the Reduced Function Device (RFD) standard. Terminal nodes and aggregation nodes are networked in a star topology, waking up from sleep mode at fixed times to actively communicate with the aggregation node. Information routing is handled by the parent (aggregation) node and coordinators and routers with routing capabilities in the network, reducing node power consumption and software implementation complexity. Aggregation nodes are an extension of the terminal node software functionality, enabling network expansion and message routing, allowing more key nodes to access the network. They can be designed according to the Full Function Device (FFD) standard. [align=center] Wireless Sensor Network Node Software Functions[/align] Gateway nodes are the coordinators required in the network, responsible for starting the network, configuring network member addresses, maintaining the network, maintaining node binding tables, etc. They are also responsible for the preliminary processing of collected data and delivering it to the traffic signal controller for transmission to the next-level information center, requiring significant storage space, computing power, and communication capabilities. Network Node Hardware Functional Design There are numerous existing wireless sensor network solutions, including microcontroller-based external RF chips and single-chip solutions integrating RF and microprocessors, offered by various chip manufacturers. Commonly used ZigBee RF chips in node design include Atmel's AT86RF230, TI's CC2420, Freescale's MC1319x and MC1320x, and Microchip's MRF24J40. In addition, chip manufacturers have launched single-chip solutions, such as the TI CC2430, which uses the architecture of the CC2420 chip and integrates the ZigBee RF front-end, memory, and microcontroller on a single chip; Freescale's MC1321x/MC1322x and Jennic's JN5121/JN513x single-chip solutions, etc. ● A typical terminal node and aggregation node design based on Atmel's AT86RF230 RF chip and AVR microcontroller is shown in Figure 4. It uses Atmel's 8-bit RISC low-power ATMegal1281V MCU as the system control core. A 512KB AT45DB041D is used as external program memory. The RF module uses Atmel's AT86RF230, which supports the ZigBee protocol and has an RF power of 3dBm, enabling outdoor transmission distances of over 300 meters. The node's expansion interfaces can connect to analog inputs, digital I/O, I2C, SPI, and UART interfaces, facilitating easy connection to sensors and other peripherals, such as external sensors for light, temperature, air pressure, sound, geomagnetism, and acceleration. ● A design based on TI's CC2420 chip and ARM microcontroller requires strong data processing capabilities to implement complex routing protocols and information processing when designing a wireless sensor network gateway. As shown in Figure 5, the Crossbow imote2 node utilizes the Marvell PXA271 high-performance, low-power processor. This processor employs dynamic voltage regulation technology, operates within a frequency range of 13MHz to 416MHz, and can function in low-voltage (0.85V) and low-frequency (13MHz) modes, exhibiting excellent dynamic power management. Furthermore, the processor integrates three chips within its package: 256KB SRAM, 32MB FLASH, and 32MB SDRAM, reducing its size. By providing various I/O pins, it can flexibly support different types of sensors. The processor also supports an MMX coprocessor to enhance multimedia processing capabilities, enabling voice and image processing in wireless multimedia sensor networks. Imote2 uses TI's CC2420 ZigBee RF chip, supporting 2.4GHz, 16-channel 250kb/s data transmission, and a transmit power of -24 to 0dBm. The effective communication distance is 30 meters, which can be increased by connecting an external antenna via an SMA interface. Imote2 System Architecture ● Node Design Other Considerations When designing nodes for a dedicated wireless sensor network in an intelligent transportation system, the following considerations are necessary: ​​① Low-power node design. Terminal nodes are all battery-powered (solar batteries are also possible). ② Low node cost. Node cost will be critical for large-scale deployments such as traffic information collection. ③ Node data processing and storage capabilities. Some nodes require high-speed information collection and the execution of recognition algorithms, thus requiring data processing capabilities. It is also necessary to consider storing programs and data within a limited space, as well as supporting online code updates. ④ Furthermore, depending on the needs of different applications, wireless sensor nodes should have different sensor interfaces to connect to various external sensors. Energy management should be a key consideration. Especially for solutions using 32-bit ARM processors with external RF chips, effective reduction of node energy consumption is necessary. Further improvements to energy management at the system-level software level are required, such as optimizing the power management functions of TinyOS or embedded Linux.