here is a need for at least 3 kinds of electronic sensors inside the beams. They would communicate with passing propulsion cars and exchange relevant information. This would serve 3 different purposes:	Figure 2:1

One group of sensors would be placed at strategic points and at regular intervals along the beams, to enable the nodes to keep track of the vehicles that move in their respective areas. These sensors will note time, speed, travelling direction and identity of every passing car, and report this to the node in charge (To be more precise, the node computer will put a time stamp on the report when it arrives, and then it will be logged in the node with that time). This would serve 2 important purposes: to quickly localize a faulty vehicle, so that other vehicles may be warned and so that rescue vehicles could be directed to the right place, if needed to serve as booking points in the point-synchronous network, for vehicles approaching a weaving node. Read more at "Emergency breaking". The second group of sensors are for vehicles looking for their berths of destination. There would be one sensor above every berth, to tell the car when it is in exactly the right position to lower the lift, as indicated by the blue dots in the illustration above (figure 2:1). Also, the buffering areas, where the cars are parked in wait for assignments, need sensors (B in the figure) to tell them when they have arrived. These sensors all need addresses, as explained elsewhere. In addition, these sensors need to be complemented by "alert sensors", indirectly telling the car how far it is to the berth of destination, so that the car won´t overshoot the berth. One such sensor would be sufficient for a station area, as indicated by A in figure 2:1 above. Since the car need to be able to identify these "alert sensors", they need addresses as well. You can read more about this on the webpage "Berthing at a stop".

Figure 2:2 The third kind of sensor is needed at every single shunt to tell the car when to lift which wheel and when to put it down. Regarding this function, see further down on this page; "the shunting". The other illustration above (figure 2:2) gives an idea how a beamcar´s positioning above a berth would be facilitated with the aid of a sensor. The sensors transmit carrier waves in the microwave-range. These would both serve to transmit data and function as radar. The range is very short, about 10-15 yards, as these waves are quickly attenuated as a function of the square of the distance from the transmitter. When a car approaches, it will be detected by this radar, and the sensor would identify itself and send a "who-are-you?" request. The car would identify itself. This identification of the car is not necessary if this is a sensor above a berth, but if it is the first kind of sensor among those listed above, this beamcar-identity would be relayed to the local node. However, the car has 2 transponders, one at each end of the propulsion car. As the car nears the sensor, those transponders will register a gradually stronger signal from the sensor. As the car slowly passes the sensor, the fore transponder will register a weaker signal, while the aft transponder will still register increasing signal strength. When both transponders get the same signal strength from the sensor, the car is in the right position.