continuous or interrupted embedded within the painted stripes are tags or labels 20 such as the one shown in fig2 each tag 20 comprises a helical antenna etched from thin aluminum or other suitable material bonded to a piece of paper at the end of the antenna is a small diode or rc network that causes the tag to emit an rf signal in response to an rf signal it receives vehicle 18 has sensors 22 24 installed as described above a processor 26 is associated with the sensors each sensor emits an rf signal at some frequency which can be the same for both sensors depending on the particular characteristic of a particular tag a particular code sometimes called backscatter will be returned to the respective sensor the particular return code can be used to identify a particular type of pavement marking such as a cross stripe ahead of an intersection a lane boundary etc the tags in stripe 12 are tuned to respond to sensor 22 while the tags in stripe 14 are tuned to respond to sensor 24 fig3 shows how a tag is embedded in a paint stripe such that the cured paint both separates the bottom face of the tag from the pavement and covers the top face of the tag as vehicle 18 is traveling sensors 22 24 are emitting low power rf signals as long as the vehicle remains within the lane sufficiently distant from the two stripes on either side the tags in the stripes will not return signals that can be detected by the sensors but if the vehicle strays to one side the corresponding sensor will begin to the receive a.