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FIELD 
     The present disclosure relates to depressible, reflective pavement markers for delineating the traffic lanes on roadways, and to a method of installing the pavement markers into a roadway that minimizes damage due to common external forces. 
     BACKGROUND 
     The statements in this section merely provide background information related to the present disclosure and may not constitute prior art. 
     The benefits of roadway lane markers to delineate traffic paths for drivers are unquestioned. Reflective pavement markers are more desirable than the usual painted dividing lines because such reflective markers can be seen over a greater distance and are easier to see in poor light or weather conditions such as rain, snow or fog. 
     Depressible pavement markers are more desirable than rigid, surface mounted markers because they are resistant to damaging impacts and shearing forces caused by vehicle tires and snowplow blades. Retractable markers have been developed to minimize damage to the reflectors. Although it protrudes above the road surface, the retractable marker may be depressed by a blow from a snowplow blade or vehicle tire. Typically, a beveled upper surface formed on the reflector protrusion provides an inclined plane across which the blade or tire rides, deflecting the protruding reflector portion of the marker downwardly into its housing. The retractable marker may include a removable retainer to enable maintenance without having to remove the entire assembly. 
     SUMMARY 
     The present invention comprises improvements to prior known pavement markers and a method of installing a resilient pavement marker able to withstand the forces of traffic and snowplows that allows for simple repair in the event of damage to the marker. 
     The resilient pavement marker of the present invention includes a housing, which may be securely imbedded within an opening in the pavement, a piston which carries a replaceable reflector assembly, and resilient biasing means urging the piston upwardly to raise the reflector assembly above the road surface. A retainer threadably engages the housing and cooperates therewith to enclose the piston and biasing means. The retainer has an aperture through which the piston may extend to raise the reflector assembly. 
     An adhesive bonds the housing within the opening in the pavement. An outer surface of the housing and a circumferential surface of the opening are contoured, and cooperate with each other to form a mechanical adhesive lock. The adhesive lock strengthens the bonding ability of the adhesive and prevents road traffic impacts and vibrations from extracting the housing. In a preferred embodiment, the adhesive is compliant and energy absorbing, to mitigate spalling around the edge of the opening in the pavement. The opening may also include a chamfer at the pavement surface to further reduce pavement spalling. 
     The retainer may include a plurality of lead-in threads. The pitch of the threads may be substantially coarser than prior known markers. The plurality of lead-in threads provides for sufficient thread engagement while substantially decreasing the number of rotations required to fully fasten the retainer to the housing, thereby facilitating quick and easy maintenance. 
     Further areas of applicability will become apparent from the description provided herein. It should be understood that the description and specific examples are intended for purposes of illustration only and are not intended to limit the scope of the present disclosure. 
    
    
     
       DRAWINGS 
       The drawings described herein are for illustration purposes only and are not intended to limit the scope of the present disclosure in any way. 
         FIG. 1  is an exploded view of a resilient pavement marker; 
         FIG. 2  is cross-sectional view of the marker of  FIG. 1 , imbedded within a roadway according to the principles of the present disclosure; 
         FIG. 3  is a cross-sectional view of a marker imbedded in a pavement opening; 
         FIG. 4  is a cross-sectional view of an imbedded marker according to the present disclosure; 
         FIG. 5  is a cross-sectional view of an another embodiment of the imbedded marker; 
         FIG. 6  is a cross-sectional view of yet another embodiment of the imbedded marker; and 
         FIG. 7  is a cross-sectional view of still another embodiment of the imbedded marker. 
     
    
    
     DETAILED DESCRIPTION 
     The following description is merely exemplary in nature and is not intended to limit the present disclosure, application, or uses. It should be understood that throughout the drawings, corresponding reference numerals indicate like or corresponding parts and features. 
     Referring first to  FIGS. 1 and 2 , there is shown a reflective pavement marker  10  embodying the present invention and adapted to be fixedly mounted within an opening  102 , formed within pavement  104 , as will be subsequently described. The pavement  104  comprises a road surface  106 . The marker  10  is intended to delineate traffic lanes of the road surface  106  in a highly visible manner. 
     The marker  10  broadly comprises a housing  20 , a piston  40  reciprocally received within the housing  20 , a reflector assembly  50  mounted to piston  40 , and resiliently compressible biasing means  70  permitting depression of the piston  40  within the housing  20  in response to surface traffic forces while ensuring return of piston  40  to its normal position. The resilient pavement marker  10  of the present disclosure provides effective reflecting to delineate traffic lanes, and is capable of withstanding the impact of vehicle tires and snowplow blades by retracting into the road surface  106 . 
     A retainer  24  is threadably received within housing  20 . Retainer  24  includes a plurality of lead-in threads  27 . After lead-in threads  27  are initially mated with cooperating threads  28  of housing  20 , retainer  24  may be rotated 540 degrees along cooperating threads  28  to fully threadably engage with housing  20 . Stated another way, one and one half rotations may be sufficient to fully threadably engage retainer  24  within housing  20 . One of ordinary skill in the art will appreciate that the number of rotations of retainer  24  within housing  20  necessary to fully engage retainer  24  therein may be more or less than one and one half rotations. Although  FIG. 1  depicts the retainer  24  having four lead-in threads  27 , one or ordinary skill in the art will appreciate that the retainer  24  could have any number of lead-in threads  27 . 
     Multiple lead-in threads  27  ensure the retainer  24  is sufficiently engaged with housing to withstand road traffic forces, while minimizing the number of rotations along cooperating threads  27 ,  28 . The pitch and depth of the threads  27 ,  28  may be customized for a given application and may be based on several factors, such as the materials of the housing  20  and the retainer  24 , the manufacturing tolerances thereof, an acceptable number of turns required to fully engage the cooperating threads  27 ,  28 , and/or any other relevant parameters. 
     One of the plurality of lead-in threads  27  may be an alignment thread  29  having a different geometric configuration than the remaining one or more lead-in threads  27 . For example, the alignment thread  29  may be larger or smaller and/or have a different cross-sectional shape than the remaining one or more lead-in threads  27 . One of the plurality of mating threads  28  can be similarly configured to threadably engage the alignment thread  29 . In this manner, the plurality of lead-in threads  27  can only engage the mating threads  28  in such a manner as to place the retainer  24  and housing  20  in an appropriate orientation relative to each other. 
     Retainer  24  must be properly aligned within housing  20  in order for reflector assembly  50  to be properly oriented relative to road surface  106 . Housing  20  and retainer  24  may include grooves  23  and  25 , respectively. The alignment thread  29  can be disposed on the retainer  24  such that engagement with its corresponding mating thread  28  will place the retainer  24  in its proper orientation relative to the housing  20 , thereby appropriately orienting the reflective lenses  51  relative to the roadway and appropriately orienting the grooves  23 ,  25  relative to each other. Once retainer  24  is fully threadably engaged within housing  20  and grooves  23 ,  25  are rotationally aligned, a pin  30  may be inserted into the grooves  23 ,  25 . Once received in grooves  23 ,  25 , the pin  30  prevents retainer  24  from rotating relative to housing  20 . As a result, road traffic forces cannot threadably disengage retainer  24  from housing  20 . 
     The retainer  24  is in the form of a sleeve with an upper aperture  34  through which the piston  40  extends. In a preferred embodiment of the present invention, the upper aperture  34  includes a plurality of lobes  36  to maintain rotational alignment of piston  40  relative to retainer  24 . The piston  40  is reciprocally received within retainer  24  such that an upper end  42  of piston  40  extends above the retainer  24  and the pavement surface  106 . Piston  40  includes a lobed peripheral surface  44  with lobes  46  that cooperate with lobes  36  of retainer  24 . This configuration allows piston  40  to reciprocate within retainer  24 , while preventing rotation within housing  20 . 
     The reflector assembly  50  may be mounted to the upper end  42  of piston  40  in order to provide reflective delineation above the pavement surface  106  under normal operating conditions. The upper end  42  shields one or more reflective lenses  51  from otherwise potentially damaging impacts from a snow plow or other vehicle, for example. The reflective lenses  51  may be disposed at about a 30 degree angle relative to the surface of the road. The reflector assembly  50  can be configured substantially as shown in  FIG. 1 , or as described in U.S. Pat. No. 5,302,048, for example, or any other suitable configuration. 
     The resiliently compressible biasing means  70  allows depression of the piston  40  into the housing  20  in response to external forces such as vehicle tires or snowplow blades, yet returns the piston  40  and reflector assembly  50  to their normal reflective position to provide delineation of traffic lanes. In a preferred embodiment, the biasing means  70  comprises a lower compression member  72 , an upper compression member  74  and a center rebound spool  76 . The spool  76  extends through axial throughbores  78  and  80  formed in the lower compression member  72  and upper compression member  74 , respectively. The lower compression member  72  fills substantially all of the space within the housing  20  below retainer  24  while the upper compression member  74  fills substantially all the space within the piston  40  thereby minimizing any empty space within which moisture, ice and debris may accumulate. It should be appreciated that the resiliently compressible biasing means  70  may be otherwise suitably configured. 
     When piston  40  is compressed, the lower compression member  72  and the upper compression member  74  are compressed against each other, evacuating the small amount of air that exists between them. This creates an air flow through a passage  90  between the lobed peripheral surface  44  of piston  40  and the upper aperture  34  of retainer  24 . This air flow purges moisture and debris that is able to accumulate within the housing  20 . 
     Referring now to  FIGS. 2-7 , the pavement marker  10  is shown imbedded in the pavement  104 . In a preferred method of installation, marker  10  is installed as an assembled unit into opening  102 . Alternatively, housing  20  may be independently installed into opening  102  before the remaining components of marker  10  are assembled into housing  20 . 
     Opening  102  is drilled in pavement  104  and a chamfer  110  may be formed on the peripheral edge  108  of the opening  102  to reduce or eliminate spalling. A compliant adhesive  120  may then be applied within the opening  102 . Housing  20  may then be inserted into opening  102  such that the adhesive  120  fixedly bonds the housing  20  therein. It should be appreciated that an alternative method of installation could include inserting the housing  20  into the opening  102  before the adhesive  120  and subsequently applying the adhesive  120  around the housing  20 . 
     The adhesive  120  may substantially fill the gap between the outer diameter of the housing  20  and the inner diameter of the opening  102 , thereby forming a moisture impervious seal around the housing  20 . A plurality of cut-outs  21  may be disposed around the bottom of the outer diameter of the housing  20  ( FIGS. 1 and 2 ). The cut-outs  21  facilitate the flow of adhesive  120  from beneath the housing  20  around the outer diameter of the housing  20 . The outer diameter of the housing  20  may also include a plurality of longitudinally extending ribs  22  ( FIG. 1 ) to facilitate bonding of the housing  20  within the opening  102  and reduce or eliminate undesirable rotation of the housing  20  within the opening  102 . 
     The compliant adhesive  120  can be a bituminous adhesive. The compliant adhesive  120  may be sufficiently compliant and compressible to absorb external impact shock and vibration, reducing spalling of the peripheral edge  108  of opening  102 . Presently preferred adhesives include BERAM 195 (McAsphalt Industries), FLEXIBLE MARKER ADHESIVE 34270 (CRAFCO, INC.), an equivalent of these adhesives, or any other adhesive with similar specifications or characteristics. The adhesive  120  may be selected to suit the construction of the marker  10 , the opening  102 , the gap therebetween, and environmental conditions of the roadway in which the marker  10  will be installed. The adhesive may harden when exposed to colder temperatures. Accordingly, for a marker installed in a cold climate, the adhesive may be softer at room temperature than the adhesive used in a warmer climate. 
     The compliant adhesive  120  fills an adhesive lock  130  formed between a contoured outer surface  132  of housing  20  and/or a contoured circumferential surface  134  of opening  102 . A contoured surface, according to the present invention, is a surface comprising a revolved profile; wherein the profile includes a plurality of directional changes. This configuration provides retention and adhesion properties that are superior to those of a simply flared housing or opening. The contoured outer surface  132  and/or a contoured circumferential surface  134  surround the adhesive  120 , mechanically reinforcing the bond between housing and opening  102 . Further, the adhesive lock  130  has more surface area to which the adhesive  120  may bond than a marker with a straight or tapered housing. Thus, the adhesive lock  130  prevents external forces, such as impact shock or vibration, from extracting the housing  20  from the opening  102 . 
     The contoured outer surface  132  of housing  20  may include a plurality of facets  142 , as shown in  FIGS. 4, 6 and 7 . The plurality of facets  142  may form a barb protuberance  140  ( FIG. 7 ). Similarly, contoured circumferential surface  134  of opening  102  may also include a plurality of facets  144 , forming an undercut  146 . Another embodiment includes a tapered circumferential surface  148  of opening  102  and/or a tapered outer surface  150  of the housing  20 . These tapered surfaces  148 ,  150  cooperate with the retention properties of the adhesive lock  130  to further enhance adhesion and the integrity of the bond between housing  20  and opening  102 . 
     The improved reliability and effectiveness of the pavement marker  10  of the present invention provides substantial cost savings in maintaining reflective traffic lanes and the roadway  106 . The adhesive lock  130  ensures marker  10  is reliably secured into the pavement  104 . The compliant adhesive  120  and the chamfered periphery  110  of opening  102  minimize pavement spalling. As a vehicle tire or snowplow blade impacts the marker  10 , the reflector assembly  50  mounted to piston  40  is depressed into the housing  20 . The subsequent compression of lower compression member  72  and upper compression member  74  forces a pulse of air through passage  90  to evacuate any moisture and/or debris that may have accumulated within the marker  10 . These features reduce the demand for maintenance to the marker  10  and the surrounding roadway  106 . The removable retainer  24  with multiple lead-in threads  27  enable quick and easy maintenance, should any be required. 
     The description of the invention is merely exemplary in nature; therefore, variations that do not depart from the gist of the invention are intended to be within the scope of the invention. Such variations are not to be regarded as a departure from the spirit and scope of the invention.

Summary:
A retractable, reflective pavement marker for delineating traffic lanes of roadways and a method of installing the same that provides improved protection from potentially damaging vehicle tires, snowplows, and environmental conditions. The marker incorporates a reflector assembly mounted to a piston that is depressible within a housing. A biasing means returns the reflector assembly to its normal position above the road surface. A compliant adhesive cooperates with an adhesive lock formed between the housing and the opening to ensure that the marker is reliably retained within the pavement. The adhesive and a chamfered opening prevent pavement spalling due to external forces. The housing includes a removable retainer through which the piston is reciprocally received. The retainer includes a plurality of coarsely pitched lead-in threads that cooperate with a threaded housing. Multiple lead-in threads provide sufficient thread engagement, while substantially decreasing the number of rotations to achieve full engagement.