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REFERENCE TO A RELATED APPLICATION AND PRIORITY CLAIM  
       [0001]     This application is a continuation-in-part of, and incorporates by reference, pending Application No. 11/055,502, filed 10 Feb. 2005, while claiming priority of that pending application, which an Issue Notification has advised will issue as U.S. Pat. No. 7,140,803 on 28 Nov. 2006. 
     
    
     FIELD OF THE INVENTION  
       [0002]     This invention relates to a passive pavement marking system that enables a motor vehicle having on-board detection equipment to detect roadway and traffic control features, such as traffic lane boundaries, intersection approaches, stop signs, and yield signs for example, and to promptly alert the driver of the vehicle and/or pedestrians and drivers of other vehicles in the immediate vicinity to the existence of potentially dangerous situations where an appropriate response to such situations may be urgently needed.  
       BACKGROUND OF THE INVENTION  
       [0003]     As discussed in the Background of the priority application, various types of traffic lane marking systems are shown in different U.S. Patents. Some use active markers, meaning markers that emit a signal of some sort, while others use passive ones, meaning that they are detected by some form of detection equipment.  
         [0004]     Examples of various systems are shown in U.S. Pat. Nos. 5,347,456; 6,411,901; 6,502,031; 6,614,469; and 6,414,606. These and other patent references are of record in the file of the priority application.  
       SUMMARY OF THE INVENTION  
       [0005]     The invention that is the subject of the priority application relates to a system and process for placement of passive markers on pavement to define traffic lane boundaries and enable a vehicle having proper detection equipment and traveling in the lane to detect the lane boundary before it is potentially violated by the moving vehicle. It is capable of providing advantages that will allow economical placement installation of passive markers on roadway surfaces, reasonable durability and life of the markers, and consequently enable economical detection systems to be used in motor vehicles.  
         [0006]     Briefly the priority application describes the use of wafer-thin elements embedded in painted traffic lane stripes such that the cured paint both separates the bottom faces of the elements from the pavement and covers the top faces of the elements. These elements utilize the same technology as used commercially in store anti-theft systems, pet identification systems, and PASS highway toll systems, and can be economically fabricated in mass-produced quantities. These elements are commonly referred to as tags or labels.  
         [0007]     On-board sensing devices are installed in motor vehicles, one on each side near the front, such as in front of each front tire at the bottom of the front bumper. The aiming of each sensing device is down and slightly outboard. Each sensing device incorporates both a transmitter and receiver. Sometimes both the transmitter and receiver are combined in one antenna frame.  
         [0008]     The wafer-thin tags or labels, which are basically miniature, disposable electronic circuits with antennas, are embedded in the paint stripes. Each tag or label responds to a radio signal of specific frequency and sufficient strength by returning a return signal. Each sensor in a vehicle emits a radio signal of predetermined frequency and strength. When such a signal is incident on an embedded tag or label, and the received strength is sufficient to cause the tag or label to issue a return signal, the return signal is picked up by the sensor receiver. Operating frequencies for RF systems generally range from 2 to 10 MHz (millions of cycles per second).  
         [0009]     The passive elements in the painted lane stripes are coded to respond based on the location of the particular stripe so that an on-board processor used for detection will be able to distinguish individual stripes on a roadway, such as distinguishing a centerline stripe that separates oncoming lanes from a shoulder stripe.  
         [0010]     When a vehicle is too close to, or actually crosses, a lane stripe, the processor detects the embedded passive elements and alerts the vehicle driver both visually, such as by flashing light, and audibly, such as by audio message. To keep the alert from coming on during turns, lane changes, and passing, the turn signals provide an input to the processor such that if the lane change/turn signal is ON, the alert is disabled.  
         [0011]     It is believed that widespread adoption of such systems can provide significant reductions in traffic accidents.  
         [0012]     Further aspects of that system and additional enhancements are the subject of this present continuation-in-part application.  
         [0013]     While roadway pavement markings that define traffic lanes are commonly referred to as paint stripes, such a paint stripe can be created, not only by painting it on a roadway surface, but also by adhering a thin strip of synthetic material to the roadway surface. The thinness of tags or labels makes them especially well suited for incorporation in such a thin piece of synthetic material.  
         [0014]     Tags may be disposed on or in such material as part of the process of fabricating roadway striping before the striping is applied to a roadway surface. For example, the striping can be a strip of plastic, or equivalent material, and the tags can be laminated within the plastic during the process of fabricating the striping at a factory. On a roadway, the striping is simply adhered to the roadway surface in conventional fashion.  
         [0015]     Tags may also be deposited on a roadway surface and then covered by the strip of plastic material as it is being laid down on and adhered to the roadway surface.  
         [0016]     Tags may also be applied to a roadway surface by mounting them on or in a small piece of plastic material that is adhered to the roadway surface. Such a piece by itself would not typically be viewed as a stripe, or ribbon, because it is not noticeably elongated. The piece however can be associated with other pieces and/or with noticeable paint stripes, either paint or plastic, to define a lane boundary or a cross stripe.  
         [0017]     A related allowed patent application, application Ser. No. 10/958,110, filed 04 Oct. 2004, relates to a stop alert warning system that is intended to alert a driver to an approaching intersection.  
         [0018]     An enhancement to that invention is provided by using tags. The tags are placed across a traffic lane that has right-of-way at an approach to an intersection where cross-traffic is obligated to stop or yield. When a vehicle having the right-of-way detects those tags, it broadcasts a short range radio signal that can received by an antenna of a vehicle in the cross-traffic roadway that is approaching or stopped at the intersection. Upon receiving the radio signal, a radio receiver in the vehicle in the cross-traffic roadway issues a visual and/or audible alert to its driver warning of the approach of the right-of-way vehicle. The received signal could also interact with the brake system of the cross-traffic vehicle to apply that vehicle&#39;s brakes with the intent of keeping the vehicle from entering the intersection. Such a system does not require any stationary active equipment in the vicinity of the intersection, such as the radar transceiver present in the system described in application Ser. No. 10/958,110.  
         [0019]     Such a system can also be used to warn a driver of a vehicle approaching an intersection upon detecting tags placed sufficiently in advance of the intersection. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0020]      FIG. 1  is a plan view of a roadway showing a single traffic lane with a motor vehicle traveling in the lane, including a representation of on-board sensors and a processor.  
         [0021]      FIG. 2  is a plan view representative of passive elements that are embedded in lane stripes.  
         [0022]      FIG. 3  is a cross section view showing an embedded element in a paint stripe.  
         [0023]      FIG. 4  is a side elevation cross section view, not necessarily to scale, of another embodiment of detectable passive lane marking before mounting on a roadway pavement surface.  
         [0024]      FIG. 5  is a side elevation cross section view through still another embodiment of detectable passive lane marking.  
         [0025]      FIG. 6  is a top plan view of yet another embodiment of detectable passive lane marking.  
         [0026]      FIG. 7  is a schematic portrayal of a roadway intersection. 
     
    
     DESCRIPTION OF THE INVENTION  
       [0027]      FIG. 1  shows a roadway  10  with painted stripes  12  and  14  defining a single travel lane  16 . A motor vehicle  18  is shown traveling in lane  16 . Each stripe  12 ,  14  may be continuous or interrupted. Embedded within the painted stripes are tags or labels  20 , such as the one shown in  FIG. 2 .  
         [0028]     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.  
         [0029]     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 .  
         [0030]      FIG. 3  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.  
         [0031]     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 return signal from the stripe toward which the vehicle is straying. The on-board system will then issue an ALERT to the driver.  
         [0032]     To keep the alert from coming on during turns, lane changes, and passing, the turn signals  28  provide an input to processor  26  such that if the lane change/turn signal is ON, the alert is disabled.  
         [0033]      FIG. 4  shows a modified construction for a stripe. Tags  20  are embedded at intervals along the length of a synthetic strip  30 . Strip  30  is fabricated by laminating the tags between layers  32  of strip  30  that are joined together in any suitable way such as by adhesive or heat bonding. The widths of the layers are greater than that of the tags so that confronting margins of the strips can be joined together along the sides of the tags thereby fully enclosing the tags within the strip. The material of the layers, plastic for example, is transparent to radio frequencies used to detect the tags and is fabricated in any suitable way, such as by cutting from thin strip material or by extrusion of plastic. Strip  30  can be applied to a roadway surface in any suitable way such as by adhesive applied to the face of the strip to be adhered to the roadway surface.  
         [0034]      FIG. 5  shows an alternate construction where the tags  20  are disposed against one face of the strip  30  rather than being laminated within the strip as in  FIG. 4 . When the strip of  FIG. 5  is applied to a roadway surface, the strip fully covers each tag, with margins of the strip extending beyond sides of the tags so that they can be adhered to the roadway surface.  
         [0035]      FIG. 6  shows another alternate construction where a tag  30  is either laminated within a small piece  34  of plastic or disposed on the lower face of the piece. Piece  34  by itself would not typically be viewed as a stripe, or ribbon, because it is not noticeably elongated. It however can be associated with other pieces and/or with noticeable paint stripes, either paint or plastic, to define a lane boundary or a cross stripe.  
         [0036]      FIG. 7  is a schematic portrayal of a roadway intersection  40  where a roadway  42  that has the right-of-way intersects one  44  on which traffic must either stop or yield to traffic on roadway  42  by virtue of a posted sign or traffic control device. One or more tags  20  are disposed on roadway  42  sufficiently in advance of intersection  40  using any one or more of the embodiments described above.  
         [0037]     Vehicles that are equipped with suitable radio apparatus are capable of utilizing tags  20  in the following way.  
         [0038]     When a vehicle  46  on roadway  42  approaching intersection  40  detects tags  20 , its radio apparatus broadcasts a short range radio signal that can received by an antenna of a vehicle  48  on roadway  44  that is approaching or stopped at the intersection. Upon receiving the radio signal, a radio receiver in vehicle  48  issues a visual and/or audible alert to its driver warning of the approach of the right-of-way vehicle. The received signal could also interact with the brake system of vehicle  48  to apply that vehicle&#39;s brakes with the intent of keeping the vehicle from entering the intersection.  
         [0039]     Rather than having two separate sensors  22 ,  24  as described above, a vehicle could have a single sensor with two antennas aimed to either side for detecting lane boundaries. In any vehicle, the antenna or antennas point in a direction or directions of interest for particular type of pavement marking being detected.  
         [0040]     While a presently preferred embodiment of the invention has been illustrated and described, it should be appreciated that principles of the invention apply to all embodiments falling within the scope of the following claims.

Summary:
Various embodiments of detectable passive markings are disclosed for application to a roadway pavement surface. Also disclosed are a system and method, using the markings, for warning cross-traffic on a roadway not having the right of way at an intersection of approaching traffic on a roadway that has the right-of-way at the intersection.