This invention relates to {HEAD ~ traffic control systems} primarily for controlling city traffic, in a grid of streets, secondarily, for {TAIL ~ street and road intersections} presently controlled by stop signs 
secondarily for
This invention relates to { HEAD ~ traffic control systems } primarily for controlling city traffic , in a grid of streets , secondarily , for { TAIL ~ street and road intersections } presently controlled by stop signs
OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH REL OTH REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH