【正文】 urther processing. A sensor node should be small in size, consume extremely low energy, operate in high volumetric densities, be autonomous and operate unattended, and be adaptive to the environment. As wireless sensor nodes are typically very small electronic devices, they can only be equipped with a limited power source of less than amperehour and volts. Sensors are classified into three categories: passive Omnidirectional sensors。 passive narrowbeam sensors。 and active sensors [3]. The sensors are implemented in this system placed beneath the roads in an intersection or on the lane dividers on each road. The sensors are active obstacle detectors that detect the presence of vehicles in their vicinity. The sensors are set in four levels on each road signifying four levels of traffic from starting from the STOP line. The fourth level indicates high density traffic and signifies higher priority for the road to the controller. The sensors required for obstacle detection can be either ultrasonic or Infrared LASER based sensors for better higher efficiency. B. Motes A mote, also known as a sensor node is a node in a wireless sensor work that is capable of performing some processing, gathering sensory information and municating with other connected nodes in the work. The main ponents of a sensor node are a microcontroller, transceiver, external memory, power source and one or more sensors [3]. Fig. 1 Block Diagram of a Mote C. Need for Motes The primary responsibility of a Mote is to collect information from the various distributed sensors in any area and to transmit the collected information to the central controller for processing. Any type of sensors can be incorporated with these Motes based on the requirements. It is a pletely new paradigm for distributed sensing and it opens up a fascinating new way to look at sensor works. D. Advantages of Motes ? The core of a mote is a small, lowcost, lowpower controller. ? The controller monitors one or more sensors. It is easy to interface all sorts of sensors, including sensors for temperature, light, sound, position, acceleration, vibration, stress, weight, pressure, humidity, etc. with the mote. ? The controller connects to the central controller with a radio link. The most mon radio links allow a mote to transmit at a distance of about 3 to 61 meters. Power consumption, size and cost are the barriers to longer distances. Since a fundamental concept with motes is tiny size and associated tiny cost, small and lowpower radios are normal. ? As motes shrink in size and power consumption, it is possible to imagine solar power or even something exotic like vibration power to keep them running. It is hard to imagine something as small and innocuous as a mote sparking a revolution, but that39。s exactly what they have done. ? Motes are also easy to program, either by using serial or Ether cable to connect to the programming board or by using Over the Air Programming (OTAP). Fig. 2 Block Diagram of the Proposed System E. Transceivers Sensor nodes often make use of ISM band, which gives free radio, spectrum allocation and global availability. The possible choices of wireless transmission media are radio frequency (RF), optical munication and infrared. Lasers require less energy, but need lineofsight for munication and are sensitive to atmospheric conditions. Infrared, like lasers, needs no antenna but it is limited in its broadcasting capacity. Radio frequencybased munication is the most relevant that fits most of the WSN applications. WSNs tend to use licensefree munication frequencies: 173, 433, 868, and 915 MHz。 and GHz. The functionality of bothtransmitter and receiver are bined into a single deviceknown as a transceiver [3]. To bring about uniqueness in transmitting and receiving toany particular device various protocols/algorithms are devised. The Motes are often are often provided with powerful transmitters and receivers collectively known as transceivers for better long range operation and also toachieve better quality of transmission/reception in any environmental conditions. F. Power Source The sensor node consumes power for sensing, municating and data processing. More energy is required for data munication than any other process. Power is stored either in batteries or capacitors. Batteries, both rechargeable and nonrechargeable, are the main source of power supply for sensor nodes. Current sensors are able to renew their energy from solar sources, temperature differences, or vibration. Two power saving policies used are Dynamic Power Management (DPM) and Dynamic Voltage Scaling (DVS). DPM conserves power by shutting down parts of the sensor node which are not currently used or active. A DVS scheme varies the power levels within the sensor node depending on the nondeterministic workload. By varying the voltage along with the frequency, it is possible to obtain quadratic reduction in power consumption. G. Tmote Sky Tmote Sky is an ultra low power wireless module for use in sensor works, monitoring applications, and rapid application prototyping. Tmote Sky leverages industry standards like USB and to interoperate seamlessly with other devices. By using industry standards, integrating humidity, temperature, and light sensors, and providing flexible interconnection with peripherals, Tmote Sky enables a wide range of mesh work applications [4]. The TMote is one of the most monly used motes in wireless sensor technology. Any type of sensor can be used