Conventionally, speed estimation from inductive loop detector is calculated by assuming a fixed effective vehicle length and dividing it with the occupancy (time). With the proposed new system, we could use a synchronized node pair with known separation to estimate the speed of a vehicle WITHOUT assuming a fixed effective length. Moreover, magnetic vehicle length could be estimated simply with the estimated speed and occupancy from each node.

Although the sensitivity of magnetometer could be slightly difference in each node, its effect could be cancelled out by taking average of the speed estimated from the Up-time pair and Down-time pair. So the major error left behind is the time synchronization between the node pair and the resolution of estimation according to the sampling rate and node separation.

A real time experiment had been conducted with 104 vehicles on local traffic for vehicle detection and speed estimation. Ground truth was provided by a video recorded during the experiment. The statistics and correlation plot are shown below: