Abstract:
A detectable warning system, for tactily signaling the presence of a terrain transition to a pedestrian, using a plurality of detectable warning domes that are arranged in a grid within a detectable warning carrier assembly. The detectable warning carrier assembly comprises a carrier layer being one of a top layer and a base layer of thermoplastic material with heat resistant detectable warning domes therebetween. The carrier layer is heated and adhered to a pavement surface. The detectable warning domes protrude from the pavement surface in an evenly spaced pattern that is detectable by the pedestrian using a cane or other guidance instrument.

Description:
CROSS REFERENCES AND RELATED SUBJECT MATTER 
   This application is a continuation-in-part of patent application Ser. No. 10/716,155, filed in the United States Patent Office on Nov. 18, 2003 now U.S. Pat. No. 6,960,989. 

   BACKGROUND OF THE INVENTION 
   The invention relates to a detectable warning system. More particularly, the invention relates to a system for easily and effectively applying prefabricated detectable warnings to pavement to provide a tactile warning to pedestrians regarding a hazardous transition. 
   It is well known that persons with little or no usable vision depend upon environmental cues—ambient sounds, edges and other physical elements that can be sensed by a cane, and texture changes underfoot—for safe and independent travel. People with low vision can also use color contrast as a navigation aid. When raised curbs do not mark and separate the pedestrian route on a sidewalk from the vehicular way, as at curb ramps, vehicle drop-offs, or depressed corners at intersections, it is difficult for some pedestrians to discern the boundary between pedestrian safety and hazard. 
   Because of the inherent danger caused by transitions without textural changes, the Americans with Disabilities Act Accessibility Guidelines (ADAAG) requires that detectable warnings be installed onto pavement or ground surfaces at certain hazardous junctures. The detectable warnings provide a contrasting texture that signals a hazardous condition to the pedestrian, and thereby informs the pedestrian to exercise care. In particular, the current regulation requires that the detectable warning consist of truncated domes having a nominal diameter of 0.9 inches, protruding from the ground surface to a height of 0.2 inches, and having a center-to-center spacing of 2.35 inches. In addition, the warning should be of contrasting color to effectively warn those who have greatly reduced vision. 
   In many cases, the warnings must be retrofitted onto existing ground surfaces. Further, the installation of such warnings is not readily compatible with standard paving techniques. Accordingly, the detectable warnings are most typically installed onto already existing pavement surfaces. 
   Some have proposed systems for the creation and installation of the domes. Generally these systems involve the use of templates to create the dome “in place”. Others have proposed systems of prefabricated warning domes. For example, TOPMARK proposes a system of preformed thermoplastic detectable warnings that is installed in sheets that have a plurality of thermoplastic domes. Unfortunately, the use of thermoplastic warning domes makes the system extremely difficult to install, since heat must be used to install the sheets, but heat will deform or destroy the thermoplastic domes. 
   My previous patent application described a system wherein warning domes are encapsulated between a top layer and a base layer of thermoplastic. The present invention contemplates a single attachment layer that both maintains the warning domes in position and adheres the dome carrier assembly to the recipient pavement surface. 
   While these units may be suitable for the particular purpose employed, or for general use, they would not be as suitable for the purposes of the present invention as disclosed hereafter. 
   SUMMARY OF THE INVENTION 
   It is an object of the invention to provide a system for allowing the effective installation of detectable warnings upon a pavement surface using heat, wherein the warning domes are not harmed during application to said pavement surface. Accordingly, the detectable warnings are made of a heat resistant casting material that is joined to a layer of thermoplastic. The thermoplastic allows the warnings to be effectively mounted and evenly distributed on the pavement surface. 
   It is another object of the invention to provide a system for allowing the easy fabrication of detectable warning dome carriers for quick and easy subsequent installation of a plurality of domes simultaneously. Accordingly, by a first embodiment, a mold is used to initially create a top layer of thermoplastic material and create the detectable warning domes thereupon. Upon removal from the mold, the detectable warning dome carriers may be easily adhered to pavement surfaces by the application of heat. In particular, the thermoplastic top layer drapes over the domes and adheres to the pavement surface. The domes themselves also rest upon the pavement surface but are held thereagainst by the top layer. Further, by a second embodiment, a mold is used to initially create the detectable warning domes, and then create a base layer thereupon within which the warning domes are adhered and partially submerged. The base layer is adhered to the pavement surface and secures the domes thereonto. 
   The invention is a detectable warning system, for tactily signaling the presence of a terrain transition to a pedestrian, using a plurality of detectable warning domes that are arranged in a grid within a detectable warning carrier assembly. The detectable warning carrier assembly comprises heat resistant detectable warning domes and an attachment layer that may be one of a top layer and a base layer. The attachment layer is heated and adhered to a pavement surface. The detectable warning domes protrude from the pavement surface in an evenly spaced pattern that is detectable by the pedestrian using a cane or other guidance instrument. 
   To the accomplishment of the above and related objects the invention may be embodied in the form illustrated in the accompanying drawings. Attention is called to the fact, however, that the drawings are illustrative only. Variations are contemplated as being part of the invention, limited only by the scope of the claims. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     In the drawings, like elements are depicted by like reference numerals. The drawings are briefly described as follows. 
       FIG. 1  is a diagrammatic perspective view illustrating a first embodiment of a detectable warning carrier assembly, having a plurality of detectable warning domes below a top layer of thermoplastic. 
       FIG. 2  is a cross sectional view of a mold used in the creation of the detectable warning carrier assembly, wherein a thermoplastic sheet has been placed to span the mold and extend across a plurality of dome forming cavities. 
       FIG. 3  is a cross sectional view similar to  FIG. 2 , except wherein heat is applied to melt the thermoplastic sheet so that it conforms to contours of the mold. 
       FIG. 4  is a cross sectional view, similar to  FIG. 3 , except wherein a heat resistant casting material has been added to the mold to form detectable warning domes within the dome forming cavities. 
       FIG. 5  diagrammatic perspective view illustrating the first embodiment of the invention installed onto a pavement surface. 
       FIG. 6  is a cross sectional view of the detectable warning carrier assembly installed on the pavement surface, as indicated by line  6 — 6  in  FIG. 5 , showing the domes resting upon the pavement surface and the top layer adhered to the pavement around the domes, holding the domes securely against the pavement surface. 
       FIG. 7  is a cross sectional view of a mold used in the creation of a second embodiment of the detectable warning carrier assembly, wherein a heat resistant casting material has been introduced into the dome forming cavities. 
       FIG. 8  is a cross sectional view of the second embodiment, wherein a sheet of thermoplastic material has covered the domes created within the dome forming cavities. 
       FIG. 9  is a cross sectional view of the second embodiment, wherein heat is applied to conform the thermoplastic materials to the domes and to adhere the thermoplastic material to the domes. 
       FIG. 10  is a diagrammatic perspective view, wherein the detectable warning carrier assembly of the second embodiment has been applied to the pavement surface. 
       FIG. 11  is a cross sectional view, taken generally in the area of line  11 — 11  in  FIG. 10 , illustrating the base layer adhered to the pavement surface, with the domes exposed thereabove and held to the pavement surface with the base layer. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   In the present application, both a first embodiment and second embodiment of the detachable warning carrier assembly,  101  and  102 , are presented.  FIGS. 1–6  illustrate the first embodiment, and  FIGS. 7–11  illustrate the second embodiment. Each of the embodiments include an attachment layer of thermoplastic material. 
     FIG. 1  illustrates a first embodiment of a detectable warning carrier assembly  101  comprising a plurality of detectable warning domes  12  arranged in an evenly spaced, grid-like pattern, and covered beneath a top layer  16 . The top layer  16  is the attachment layer in the first embodiment. The carrier assembly  101  is substantially planar in between detectable warning domes  12 . The domes  12  are preferably truncated, such that they are flattened on top. 
   To facilitate proper application of the detectable warning carrier assembly  101 , the top layer  16  is preferably made of thermoplastic. The use of thermoplastic allows the top layer  16  to melt so as to conform to the contours of the recipient surface, and to effectively bond with said recipient surface by flowing into cracks and pores present thereon. 
   Referring to  FIG. 2 , formation of the first embodiment of the detectable warning carrier assembly centers upon a mold  20  having a top surface  22  and a plurality of dome forming cavities  24  extending downwardly from the top surface  22 . The dome forming cavities  24  are shaped like inverted truncated warning domes and are spaced apart as required by regulations such as ADAAG 4.29.2, and to otherwise function as an effective detectable warning. The dome forming cavities  24  are dimensionally modified to accommodate a coating of thermoplastic as will be apparent hereinafter. 
   A first sheet of thermoplastic  26  is illustrated extending across the top surface  22 , spanning the mold  20 , and thereby extending across all dome forming cavities  24 . The first sheet of thermoplastic  26  may actually be numerous sheets of thermoplastic that are adjacent and/or overlap each other so that they together substantially span the top surface  22  of the mold  20 . 
   Referring now to  FIG. 3 , heat  28  is applied to the thermoplastic sheet  26  to a temperature sufficient to substantially melt the first sheet of thermoplastic, so that it forms a one-piece, continuous, top layer  16  of the detectable warning carrier assembly  101  being formed. Accordingly the top layer  16  flows into the dome forming cavities  24  where it conforms to the mold  20 , taking the shape of the dome forming cavities  24 , and spanning the top surface  22  with one continuous piece. The top layer  16 , however, is substantially thin, and thus does not fill the dome forming cavities  24 , nor does it substantially obscure the topography thereof. 
   Referring now to  FIG. 4 , heat resistant casting material  30  has been added to substantially fill each of the dome forming cavities  24 . In particular, the dome forming cavities  24  have been filled to a height substantially equivalent to the top surface  22 , or more particularly—to substantially the height of the top layer  16  as it extends across the top surface  22 . The heat resistant casting material is flowable but settable, hardens in time, and is preferably a masonry material such as concrete. Note that the casting material is shown as uneven at its uppermost surface—this is to emphasize its flowability and viscosity. The casting material will, however, settle and form a substantially flat dome base surface  12 A, as seen in  FIG. 6 . Preferably the dome base surface  12 A is substantially coplanar with the top layer  16 . Note that prior to the addition of the casting material, sand may optionally be sprinkled into the mold, while the thermoplastic is still hot, to adhere to the not-yet-cured top layer. Such sand may be added to facilitate a strong bond between the casting material and the thermoplastic top layer. Alternatively, formable heat resistant plastic, such as thermosetting plastic, may be introduced into the mold to form the domes. Once set, such plastic will resist subsequent melting, but may melt slightly on the surface sufficient to establish a strong bond between the dome and top layer  16 . In general, a variety of heat resistant materials can be used for the domes  12 , including chemical compounds, mixtures, resins, polymers, glass, organic or inorganic substances, metals or other materials that have heat resistant properties. An important parameter of the heat resistant casting material is that it can resist temperatures of approximately 300–500 degrees Fahrenheit, so as to endure the bonding process that will be subsequently described. 
   If additional strength is desired, a strengthening grid, such as a mesh material, can be introduced at this point. Accordingly, such a mesh grid can be placed upon the top layer  16  so that it substantially spans the mold, and adheres to all domes. The additional strength provided by the strengthening grid helps make the invention more suitable for use on a surface where vehicles or other heavy equipment might be used. 
   In this regard, rather than casting the domes in place, performed domes can be introduced into the mold, with or without a pre-existing mesh grid holding a plurality of domes together. For example, the domes may be injection molded in a group, wherein members that connect the domes together are simultaneously formed during the injection molding process. The entire grouping of domes can then be placed within the dome forming cavities with the connecting members extending parallel to the top surface  22  of the mold  20 . In such a case, the domes are made of a heat resistant plastic material. In addition, a plurality of domes can be joined and mounted upon a veneer of brick or other earthen material. The domes and veneer are then placed into the mold, with the domes resting against the top layer  16  within the dome forming cavities. The domes and veneer (along with adjacent veneers holding their own domes) are then adhered to the thermoplastic material by any suitable means. 
   Referring now to  FIG. 5 , to install the detectable warning carrier assembly  101 , the top layer  16  is placed upon a pavement surface  40  near a hazardous transition point  42 , which also places the dome base surfaces  12 A upon the pavement surface (best seen in  FIG. 6 ). In the environmental context provided within  FIG. 5 , a curb cut  44  creates the transition point  42  at which it is necessary to provide a textured, tactile warning. When suitably positioned adjacent to the hazardous transition point, and trimmed to fit, heat is applied to partially melt the top layer  16 . A simple torch may be used to supply the necessary heat. As the top layer  16  melts, it will flow into cracks, crevices, and pores of the pavement  40 . Once it has been allowed to cool, it remains permanently attached to the pavement  40 , and the domes  12  will provide tactile feedback to any pedestrian approaching the transition point  42 . 
   Referring to  FIG. 6 , the substantially flat dome base surfaces  12 A of each dome rest upon the pavement surface. The top layer  16  both covers and drapes downwardly over each of the domes  12  and then extends substantially coplanar with their base surfaces  12 A, such that the top layer  16  can adhere to the pavement surface  40  and hold the domes  12  downwardly thereagainst. 
     FIGS. 7  thru  11  illustrate a second embodiment of the detectable warning carrier assembly  102 . In the second embodiment, a base layer  14  is employed as the attachment layer—to both maintain the positioning of the domes  12  and to adhere to a recipient pavement surface. 
   Formation of the second embodiment is illustrated in  FIGS. 7  thru  9 . In  FIG. 7 , the heat resistant casting material  30  has been added directly into the mold to partially fill the dome forming cavities  24  of the mold  20 . In particular, the heat resistant casting material  30  is added until it substantially reaches the top surface  22  of the mold  20 . What will become the dome base surfaces  12 A are shown as uneven in an exaggerated sense to emphasize the flowability of the casting material. The dome base surfaces  12 A are still, in fact, preferably somewhat uneven to facilitate secure attachment to the base layer  14  as will be illustrated hereinafter. 
   In  FIG. 8  a second sheet of thermoplastic material  32  has been overlaid upon the mold, spanning the top surface thereof, to coat the detectable warning domes  12  and with a continuous piece of thermoplastic material to form the base layer  14 . In particular, the second sheet of thermoplastic material  32  spans the mold  20 , covers all the detectable warning domes  12  (inverted and within the dome forming cavities). Then in  FIG. 9 , heat  28  is applied to bring the second sheet of thermoplastic material  32  into a melted or plastic state so that it flows to adhere to the base surface  12 A of the detectable warning domes  12 . Thus, the second sheet of thermoplastic material  32  becomes the base layer  14  of the detectable warning carrier assembly  102 . To facilitate the adhering to the base surface  12 A, sand may be sprinkled over the domes  12 , or other means employed to facilitate a secure joint between the domes  12  and base layer  14 . 
   After cooling, the detectable warning carrier assembly  102  may be removed from the mold—by separating the base layer  14  from the mold. The carrier assembly  102  is then inverted. As seen in  FIG. 11 , when fabricated carefully, the base layer  14  is substantially planar, and the domes  12  are mounted thereon. 
   Referring to  FIG. 10 , to install the second embodiment of the detectable warning carrier assembly  102 , the base layer  14  is placed upon the pavement surface  40  near the hazardous transition point  42  created by the curb cut  44 . When suitably positioned adjacent to the hazardous transition point, and trimmed to fit, heat is applied to partially melt the base layer  14 . A simple torch may be used to supply the necessary heat. As the base layer  14  melts, it will flow into cracks, crevices, and pores of the pavement  40 . Once it has been allowed to cool, it remains permanently attached to the pavement  40 , and the domes  12  provide tactile feedback to any pedestrian approaching the transition point  42 . The domes  12  are exposed above the base layer  14 . As illustrated in  FIG. 11 , the base layer  14  rests upon the pavement surface  40  to which it is adhered, the domes  12  are themselves adhered to the base layer  14 . 
   In conclusion, herein is presented a detectable warning system for use on a pavement surface. The invention is illustrated by example in the drawing figures, and throughout the written description. It should be understood that numerous variations are possible, while adhering to the inventive concept. Such variations are contemplated as being a part of the present invention.