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CROSS-REFERENCE TO RELATED APPLICATIONS 
     STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH 
     Not applicable. 
     BACKGROUND OF THE INVENTION 
     Highway snow and ice control frequently is carried out by governmental authorities with the use of dump trucks, which are seasonally modified by the addition of snow-ice treatment components. These components will include forwardly-mounted plows and rearwardly-mounted mechanisms for broadcasting materials such as salt or salt-aggregate mixtures. The classic configuration for the latter broadcasting mechanism includes a feed auger extending along the back edge of the dump bed of a truck. This hydraulically driven auger effects a metered movement of material from the bed of the truck into a rotating spreader disc or “spinner” which functions to broadcast the salt across the pavement being treated. To maneuver the salt-based material into the auger, the dump bed of the truck is progressively elevated as the truck moves along the highway or pavement to be treated. 
     Operating systems employed for these snow and ice control implements have been substantially improved over the past decade. An initial such improvement has been achieved through the utilization of microprocessor driven controls over the hydraulics employed with the seasonally modified dump trucks. See Kime, et al., U.S. Pat. No. Re 33,835, entitled “Hydraulic Systems Used with Snow-Ice Removal Vehicle, reissued Mar. 3, 1992. This Kime, et al. patent describes a microprocessor-driven hydraulic system for such trucks with a provision for digital hydraulic valving control which is responsive to the instantaneous speed of the truck. With the hydraulic system, improved controls over the extent of deposition of snow-ice materials is achieved. 
     This form of control has been employed to control the rate of salt deposition such that the granular material may be ejected from a delivery vehicle at a rate commensurate with the trucks forward speed. Such an arrangement conserves snow-ice materials and permits deposition at desirably higher truck speeds. See in this regard, Kime, et al, U.S. Pat. No. 5,318,226 entitled “Deposition of Snow-Ice Treatment Material from a Vehicle with Controlled Scatter”, issued Jun. 7, 1994. This approach is sometimes referred to as a “zero-velocity” method for salt distribution. 
     Investigations into the chemical-physical phenomena of pavement borne ice formation have recognized the importance of salt in the form of a salt brine in breaking the bond of ice with underlying pavement. It is this brine, as opposed to mere granular salt, which reacts to attack ice formations. This phenomenon has lead to the development of improved techniques for generating brine of sufficient concentration to break the ice-pavement bond. For example, Kime in U.S. Pat. No. 5,988,535 entitled “Method and Apparatus for Depositing Snow-Ice Treatment Material on Pavement”; issued Nov. 23, 1999 describes the deposition of a granular salt-brine material on pavement as a continuous narrow band. The result of such deposition is a highly effective snowice treatment procedure with an efficient utilization of salt materials. An improvement in this technique is described in application for U.S. patent application Ser. No. 09/512,199 entitled “Method and Apparatus for Depositing Snow-Ice Treatment Material on Pavement” by Kime, filed Feb. 24, 2000 in which narrow band ejection of salt and brine is provided in a manner wherein it is encountered by the rear drive wheels of a dump truck. For both approaches of the above-described narrow band deposition, the dump truck structuring is such that use may be made of them for purposes other than snow-ice control during winter seasons. In this regard, highway maintenance organizations require that the dump trucks be capable of being used for such purposes as hauling gravel and/or pothole repair materials. 
     While substantial improvements have been recognized as with these brine formation snow-ice control systems, the majority of highway maintenance organizations continue to employ conventional highway maintenance dump trucks which are retrofitted each season with plows, a cross-bed auger which typically is bolted to the truck bed beneath the bed tailgate and a hydraulically driven spinner. Control over the rate of material feed generally is by the truck operator. When these trucks are utilized for winter maintenance purposes, the plows are uncoupled; the augers are covered with a plate arrangement and the spinner may be removed or pivoted out of the way. With the emergence of the above-rioted ice-pavement bond studies, the ubiquitous snow-ice control retrofit approaches now are called upon to additionally mount relatively large brine tanks which permit a substantially increased utilization of brine in combination with granular salt. The brine preferred, in terms of cost, is a sodium chloride solution. However, the amount of this form of brine called for in snow-ice treatment is quite substantial compared to alternate brines, such as calcium chloride based solutions which typically are orders of magnitude greater in cost but lower in amounts or volumetric requirements. Typically, the only practical location for the brine tanks is at the rear of these trucks, regions between the axles exhibiting little or no space for tank mounting. These polymeric tanks, in addition to being bulksome, when filled with brine solution are quite heavy and difficult to maneuver on and off trucks. 
     The Ohio Department of Transportation (ODOT) developed a combination tailgate assembly for winter season use. This assembly mounts the brine tanks at the rear of a tailgate and couples both the spinner and auger at the bottom of the tailgate. The combinational assembly then is mounted on a truck utilizing a conventional front-end loader. The maximum available brine tank capacity for the assemblies is about 70 gallons. An undesirable aspect of these devices resides in a rearward diversion of the center of gravity of the tailgate to the extent that, when the dump bed is raised, the tailgate will open only a few inches when the brine tanks are empty and not at all should they be filled. However, these combinational tailgate assemblies represent a substantial improvement in terms of convenience of mounting over the conventional bed-mounted auger-spinner approach. 
     On occasion, the dump trucks will be loaded with both salt and brine and sent out on patrol prior to the commencement of inclement weather. Where such weather fails to materialize, then these trucks will return to base at which point in time it is necessary that the salt load be dumped. Because the tailgates cannot be opened, it then becomes necessary to again use the front-end loader approach to remove the combinational tailgates entirely in order to carry out necessary salt dumping. The same problem is encountered where the trucks, for example, are dispatched to carry out plowing alone without salt treatment. To achieve necessary traction, the trucks are loaded with salt notwithstanding the fact that such salt is not dispersed. Accordingly, as the trucks return, again it is necessary to dump the salt, which cannot be carried out without removal of these non-pivoting combinational tailgates. 
     BRIEF SUMMARY OF THE INVENTION 
     The present invention is addressed to a vehicle and associated tailgate assembly, the latter being configured for snow-ice control procedures. Employing a tailgate frame supporting brine supply tanks which extend through that frame and pivotally mounting the frame rearwardly of a normal pivot position, the tailgate functions in a manner wherein its center of gravity resides at a vertical plane passing through the rearwardly disposed pivot connection. Thus, the tailgate assembly may pivot open when the vehicle dump bed to which it is attached is raised, having been unlatched by the operator. This opening occurs even though the tailgate carrying brine tanks may be full of brine fluid. 
     Liquid brine fluid weight distribution achieving the desired tailgate center of gravity is developed through the use of a tank cross section resembling an inverted, truncated right triangle. Thus configured and oriented, the tank assembly extends inwardly through the tailgate frame. With this arrangement, substantial enhancement of the volumetric capacity also is realized while desired opening pivoting performance of the tailgate is achieved. In this regard, for a preferred embodiment, tank capacity is elevated from about 70 gallons to about 140 gallons and this enhancement is evolved with a desired truck rear end tank mounting. 
     Carried by the tailgate frame beneath the brine tank assembly is a cross transport mechanism implemented as an auger carrying a sequence of flights which are driven from first to last to maneuver particulate material essentially across the widthwise extent of the vehicle dump bed into an outlet . From this outlet the material passes to a broadcasting assembly implemented as a hydraulically driven spinner. The feed opening of this auger is an elongate one generally presented to the widthwise extent of the dump bed of the vehicle. Ingress of the salt material into the auger for distribution to the outlet is made possible and facilitated by the noted sloping forward wall of the brine tank assemblage. That sloping wall serves to overcome any tendency of the granular salt materials to “bridge” or coalesce and fail to move towards the auger-based transport mechanism. 
     Because it is desirable to admix a substantial amount of brine fluid with particulate salt materials, fluid brine from the brine tank assemblage is introduced to that granular salt at a location adjacent the noted last flight of the auger assembly. Thus, the last flight is utilized as a mixing device for developing a brine-salt slurry ultimately to be deposited or broadcast from the spinner assembly. 
     Simple mounting of the tailgate assembly to the rims of the dump bed walls at the rearward portion of the dump bed is carried out utilizing two links, one positioned at each side of the tailgate and having rearward apertures formed therein pivotally coupled with the upper region of the tailgate frame. Each link additionally contains a medial aperture and a forward aperture. In this regard, medial aperture is connected with the “normal” tailgate pivoting mechanism attached to the dump bed rims. The forward aperture is coupled with an installed stabilizing bracket through the utilization of pin connections for the latter two apertures. Mounting of the tailgate assembly to the dump bed readily is carried out utilizing, for example, a front end loader. 
     Other objects of the invention will, in part, be obvious and will, in part, appear hereinafter. 
     The invention, accordingly, comprises the apparatus possessing the construction, combination of elements and arrangement of parts which exemplify the following detailed description. 
     For a fuller understanding of the nature and objects of the invention, reference should be had to the following detailed description taken in connection with the accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a left side elevational view of a truck outfitted with apparatus according to the invention showing its tailgate assembly in a closed orientation; 
     FIG. 2 is a left side elevational view of the truck of FIG. 1 showing an elevated dump bed with the tailgate assembly in a latched orientation; 
     FIG. 3 is a left side elevational view of the truck of FIG. 1 showing an elevated dump bed and a tailgate assembly released for pivotal outward movement; 
     FIG. 4 is a left side elevational view of a truck having a modified tailgate configured in accordance with the prior art and showing the tailgate in a released orientation for opening; 
     FIG. 5 is a rear view of the truck of FIG. 1; 
     FIG. 6 is a sectional view taken through the plane  6 — 6  in FIG. 5; 
     FIG. 7 is a plan view of the forward facing side of the tailgate assembly employed with the vehicle of FIG. 1; and 
     FIG. 8 is a partial top view of the truck of FIG.  1 . 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring to FIG. 1, a utility vehicle retrofitted for the seasonal duties of snow-ice removal is revealed generally at  10 . Configured as a dump truck, vehicle  10  includes a cab  12  and hood  14  mounted upon a frame represented generally at  16 . Frame  16  is supported upon pavement represented at  18  by four wheel assemblies, two of which are revealed at  20  and  21 . At the forward end of the vehicle  10 , there is mounted a front snowplow  24  which is removed by maintenance personnel when the vehicle  10  is called upon for winter duties other than snow-ice control. The front plow  24  is elevationally maneuvered by up-down hydraulic cylinder assembly  26 . Additionally, this front plow  24  is laterally, angulary adjusted by left-and right-side hydraulic cylinder assemblies, the left side one of which is represented at  28 . Not shown in the figure is a wing plow which is mounted adjacent the right or left fender of the vehicle  10 , and which functions generally as an extension of the front plow  18 , serving to push snow off of a shoulder. Also not shown is an underbody scraper plow which is a heavy duty plowing apparatus mounted beneath the vehicle  10  and which functions to utilize the weight of the vehicle  10  to peel or remove hard packed ice or snow at the pavement  18 . Vehicle  10  supports a dump bed represented generally at  30 . Looking additionally to FIG. 8, the bed  30  is seen to be formed with oppositely disposed sides  32  and  34  which are spaced apart a bed width and extend with the bed floor  36  to a bed end  35 . These sides  32  and  34  extend upwardly from bed floor  36  to respective bed rims represented at  38  and  40 . Rims  38  and  40  are seen to be slightly elevated at rear posts adjacent the rear end of  42  of bed  30  as shown respectively at  44  and  46 . 
     As revealed additionally in FIGS. 4 and 8 rim elevated portions  44  and  46  support respective upstanding, generally u-shaped pin retention brackets  48  and  50 . Brackets  48  and  50  function with robust rigid pins or connectors shown respectively at  52  and  54  (FIG. 8) which are located to define “normal” pivot mechanisms at “normal” pivot positions which will be encountered with a standard tailgate assemblage. In this regard, the “normal” pivot position provided by the bracket and pin mechanisms  48 - 52 ,  50 - 54  are somewhat centered upon the respective elevated rim components  44  and  46 , i.e., forwardly of bed end  35 . 
     The rearward region of dump bed  30  supports a tailgate assembly represented generally at  60  within which there are integrated snow-ice control features including an auger, a spinner, and importantly, a brine tank storage arrangement having a volumetric capacity which is substantially improved over assemblies of the past. The latter feature is so integrated and configured within the frame of the tailgate assembly  60  that the tailgate will open even though the brine tanks may be full and, thus, the assembly  60  may remain in place as vehicle  10  is used for purposes other than snow-ice control, i.e., transporting gravel and/or pothole repair materials during the winter season, no temporary removal being required. 
     Integrated features of the tailgate  60  are realized through the utilization of an open rigid tailgate frame represented generally at  62 . FIGS. 5 and 6 reveal that the frame  62  includes upper and lower steel transverse box beams  64  and  66  which, in general, have a widthwise extent corresponding with the widthwise extent of the dump bed  30 . FIG. 6 and 7 reveal that the beams  64  and  66  are parallel and weldably joined to and spaced apart by an upstanding, relatively wide rearwardly opening channel-shaped side member seen in FIGS. 5 and 7 at  68 . The opposite or right side of the frame  62  is configured having an upstanding box beam (not shown) which is welded to and extends between the transverse beams  64  and  66 . Thus, a form of open frame assembly is provided. FIGS. 5,  7  and  8  reveal that the frame  62  is pivotally connected to the dump bed  30  at rear region  42  by oppositely disposed tailgate pivot mechanisms represented generally at  70  and  72 . The tailgate mounted components of these mechanisms are provided as an outwardly extending upwardly disposed shaft or pin and support plate  74  at mechanism  70  and a corresponding outwardly horizontally extending shaft or pin and support plate  76  at mechanism  72 . The pins of these assemblies  74  and  76  are seen, as represented in FIGS. 1-3 and  8 , to pivotally extend through the outboard or outer apertures of respective steel links  78  and  80 . These figures reveal that in addition to this pivotal connection with the tail gate frame  62 , the links  78  and  80  form two additional forwardly disposed connections one at a middle or medial aperture which receives an earlierdescribed “normal” pivot position located pin. In this regard, for example, “normal” pivot position pin connector  52  is elongated to extend into an auxiliary bracket  56  (FIG. 8) and through the middle aperture of link  78 , while “normal” pivot position pin  54  is elongated to extend into an auxiliary bracket  58  and through the corresponding middle aperture of link  80 . To stabilize these links  78  and  80  from rotation tendency about these central connections at pins  52  and  54 , the links  78  and  80  are each formed with an inward or forward aperture, which is engaged by respective pins  82  and  84 . Pins  82  and  84  are retained in position by virtue of their connection with respective bifurcate stabilizing brackets  86  and  88 . These brackets  86  and  88 , in turn, are weldably connected with bed rim  38  of side  32  and bed rim  40  of side  34 . With the pinned assemblage shown, the entire tailgate assembly may be pivotally mounted upon and removed from the rearward region  42  of dump bed  30 . 
     The center of gravity exhibited by the thus pivotally connected tailgate assembly  60  is developed through a combination of positioning the upper tailgate frame pivots  74  and  76  rearwardly from the normal pivoting location represented at pins  52  and  54 , and rearwardly from the bed end  35  and by supporting the brine tanks through the tailgate frame  62 . The tanks are arranged such that they extend forwardly through frame  62  and are retained therein by an assembly of brackets and side plates represented in general at  90  in the rear view shown in FIG.  5 . That bracket and side plate assembly  90 , in turn, is weldably connected to the tailgate frame structure  62 . FIG. 5 reveals the presence of three polymeric brine tanks  92 - 94  retained by this assembly of brackets, bottom support structure and side plates. That figure shows the somewhat normally vertically oriented rear walls of tanks  92 - 94  respectively at  96 - 98 . Extending from the bottom wall of each of the tanks  92 - 94  are lower disposed brine outlet port assemblies, each comprised of right and left output ports. In this regard, tank  92  is formed with left output and right output-input ports shown respectively at  100  and  101 ; tank  93  is formed with left and right output-input ports shown respectively at  102  and  103 ; and tank  94  is shown with left and right output ports  104  and  105 . Port  105  is coupled with a combined fill and drain valve  112  functioning with part  105  as an input assembly as well as a drain valve. Ports  103  and  104  are connected by a polymeric conduit  108  which functions to couple tanks  93  and  94  in fluid transfer or cascading relationship. Similarly, ports  101  and  102  are connected by a polymeric conduit  110  which serves the same fluid transfer or cascading function. That fluid transfer function performs in either of two directions. The tanks are draining in a rightward brine emptying application by opening outlet valve  112  coupled to port  105  or in a leftward sense delivering brine to the salt dispensing function via polymeric conduit  114 . The tanks are filled by injecting brine under pressure into an open valve  112 , filling being carried out in a cascading manner. Venting as described later herein facilitates the filling and draining procedure. Certain of the components of the assembly brackets, bottom support frame and side plates  90  are seen in FIG. 5 as a rearward top support bracket  120 ; right side plate assembly  122 ; left side plate assembly  124  and a bottom support frame represented generally at  126 . A downwardly sloping rearward protective metal shield is seen at  139 . 
     Looking momentarily to FIG. 8, right and left side plate assemblies  122  and  124  again are revealed in conjunction with top rearward support bracket  120  and top forward support bracket  128 . In the figure, the top walls of tanks  92 - 94  are shown respectively at  130 - 132 . Each of the top walls includes an upwardly disposed brine tank vent assembly, the circular openings of which are shown respectively at  134 - 136 . These vents are positioned forwardly in adjacency with the vertical wall portions of the tank forward walls. This avoids spillage when bed  30  is lifted. Note in the figure that the top walls  130 - 132  extend inwardly or forwardly from the frame  62 . With this arrangement, when the tanks  90 - 94  are filled with brine, the substantial weight represented by the loaded tanks will be partially shifted forwardly and, concomitantly the center of gravity is moved closer to a vertical plane extending through frame  62 . This forward shift is effective to permit the tailgate assembly  60  to open to an extent fully adequate to permit unfettered dumping activities. 
     A transverse cross-section revealing the profiles of tanks  92 - 94  is shown in FIG.  6 . Looking to that figure, the tank  93  again is seen to be secured along the edges of its top wall  131  by top rearward support bracket  120  and top forward support bracket  128 . The bottom wall  138  of tank  93 , incorporating the right fluid conveyance port  103 , is seen to be ultimately supported by an elevated platform portion  140  of bottom support  126 . The forward wall  143  of tank  93 , as well as the corresponding forward walls  142  and  144  of respective tanks  92  and  94 , are formed integrally with bottom walls as at  138  and top wall  131  but slope angularly forwardly from their bottom walls as at  138  to vertical portions which are formed integrally with top walls as at  131 . Thus, forward wall  143  extends to vertical wall portion  147  which, in turn, is formed integrally with top  131 . The configuration of tanks  92 - 94  wherein the inwardly facing tank walls as at  142 - 144  slope upwardly inwardly evolves two necessary aspects of the tailgate assembly of the invention. First, the inwardly depending nature of these forward walls  142 - 144  shifts the center of gravity of the tailgate assembly  60  inwardly or forwardly when the tanks are loaded with brine. Next, the slope permits and, in fact, facilitates the movement of salt within the truck bed  30  into a bed cross transport mechanism implemented as an auger. In this regard, should the tanks  92 - 94  have been provided with a rectangular cross-sectional configuration, salt would not be able to flow along the dump bed  30  into that cross transport mechanism. 
     The slope of walls  142 - 144  is about 34° with respect to vertical or 56° with respect to the tank bottom walls. Note that this figure reveals the rearward protective metal shield, as well as a downwardly sloping forward protective metal shield  141 . 
     The above-noted cross bed transport mechanism is represented in general at  160 . Mechanism  160  is implemented as an auger represented generally at  162  which extends adjacent a back plate portion  164  and bottom plate portion  166  of bottom support  126 . That bottom support  126  is seen to be weldably connected to lower transverse frame member  66 . FIG. 7 reveals that the auger  162  is comprised of two flight regions represented generally at  168  and  170  which are mounted upon a common shaft  172 . The motion of travel of granular material will be from the region  170  toward the region  168 , the latter region extending to a wetting and dispensing function. Note that a flight structure of larger diameter is provided at region  168 . Shaft  172  is supported between a bearing assembly  174  and a hydraulic motor  176 . To protect the transport mechanism  160  when the vehicle  10  is utilized for duties other than snow-ice control, the region surrounding it is enclosed by an elongate protective plate or buffer  178 . In this regard, the plate  178  is manipulated by an external arm or crank such that it is manipulated into the orientation shown in sold line fashion in FIG. 6 during active use of the transport mechanism  160  and is maneuvered to the downwardly directed orientation represented in phantom at  178 ′ when the transport mechanism  160  is not in use. To provide protection for the forward walls  142 - 144  of polymeric tanks  92 - 94 , a thin metal shield  180  is positioned in abutment with the outer surface of these inwardly directed walls. 
     Cross bed transport mechanism  160  feeds granular salt material, i.e., salt, into a broadcasting assembly represented in general at  182 . Looking to FIG. 5, assembly  182  is seen to comprise a cylindrically shaped feed input chamber  184  pivotally mounted over shaft  172 . Downwardly depending from the input chamber  184  and pivotal therewith is a feed chute  186  extending to a chute opening  188 . Mounted upon the chute  186  at a location just below opening  188  is a drivably rotatable disc or “spinner”  190 . Disc  190  supports a plurality of vanes two of which are shown at  192  and  194 . The disc  190  is rotatably mounted upon a disc platform  196  which, in turn, is supported from the feed chute  186  by brackets  198  and  200 . A hydraulic motor  202  is supported upon the underside of platform  196  and is coupled in driving relationship with the disc  190 . Accordingly, with the maneuvering of granular material into the feed input chamber  184 , such material drops upon the rotating disc  190  and is broadcast upon the roadway or pavement  18 . 
     In keeping with current procedures calling for the utilization of substantial amounts of brine in combination with granular salt material to attack the ice-pavement bond, brine from the enhanced capacity tanks  92 - 94  is delivered to the feed input chamber  184 , whereupon it is directed via a rigid polymeric pipe seen in phantom at  210  to be expressed into the final flight components of the auger  162 . This provides for an improved mixing of the brine with particulate salt material and the result is a form of granular salt and brine slurry which is delivered into the chamber  184 , through chute  186  and on to the disc  190  for broadcasting. This brine fluid is drawn from conduit  114  through a check valve (not shown) by a hydraulic pump  212  which is driven, in turn, by a hydraulic motor  214 . Motor  214  and pump  212  are mounted upon a bracket  216  which in turn, is weldably connected to left side plate assembly  124 . Driven association between the motor  214  and pump  212  is through a coupling  218 . Additionally, coupled to conduit  214  is a shutoff valve, the hand actuated lever for which is represented at  219 . The output of pump  212  is provided at a flexible conduit  220  extending to the input of pipe  210 . 
     The control system for operating hydraulic motors  176  and  214  as well as spinner motor  202 , in general, may be combined with the overall vehicle hydraulic system. That system also will control plow orientations and the dump bed. A variety of these systems are available. However, a preferred arrangement is the microprocessor driven system described in U.S. Pat. No. Re 33,835 (supra) which is incorporated herein by reference. 
     FIGS. 5 and 7 further reveal that the tailgate frame  62  supports two, oppositely disposed closure assemblies  230  and  232  which are provided for the present embodiment, as outwardly extending latching pins configured in conventional manner. These pins  230  and  232  are engagable by a conventional bayonet-type quick disconnect cam latch or tailgate latch. In this regard, tailgate latch  234  is shown engaging latching pin  230  and tailgate latch  236  is shown engaging latching pin  232 . In conventional fashion, these latches  234  and  236  are actuated to open and closed orientations by an operator lever (not shown) typically located upon the bed  30  adjacent cab  12 . 
     FIGS. 5 and 7 further reveal the presence of two, spaced apart lift connectors  238  and  240  which are welded to transverse box beam  64 . These connector devices are utilized in conjunction with, for example, a front end loader to maneuver the tailgate assembly  60  on to and off of dump bed  30 . 
     Returning to FIG. 1, the dump bed  30  is shown in its down position preparatory to being loaded with snow-ice control material. A lever  242  coupled to baffle or protective plate  178  (FIG. 6) is shown in an orientation wherein that plate  178  is in its upper or solid line orientation shown in the latter figure. Feed chute  186  is shown in a vertical orientation and disc  190  is in a horizontal orientation. The latches as at  234  and  236  have engaged the latching pins  230  and  232  to retain the tailgate assembly  60  in securement against the rear region  42  of dump bed  30 . 
     Looking to FIG. 2, dump bed  30  is shown in an orientation having been elevated by a hydraulic cylinder arrangement  244  in the course of salt deposition. In this regard, the latches  234  and  236  remain in engagement with respective latching pins  230  and  232 . Note that the feed chute  186  remains in a vertical orientation and disc  190  remains in a horizontal orientation. 
     Assuming that the driver of the vehicle  10  has returned to base at the end of a patrol with a quantity of granular salt material within bed  30  as well as brine within tanks  92 - 94 , then it is necessary to dump that remaining salt at the storage facility. The arrangement of tailgate  60  permits that to occur. Looking to FIG. 3, the dumping orientation for such a situation is revealed. The operator has released the cam latches  234  and  236 . Because the pivot position for the tailgate  60  has been moved to the pin position  74  spaced rearwardly from the normal position, for example, at  52 , and because the forward walls  146 - 148  of brine tanks  92 - 94  extend forwardly through the tailgate frame assembly  62 , the center of gravity of the entire assembly  60  has been moved forwardly. That center of gravity lies within a plane represented at vertical dashed line  246 . Note that the tailgate assembly  60  is adequately open to permit dumping of the remaining salt. This condition will obtain even though the brine tanks  92 - 94  are filled with brine. 
     Where the vehicle  10  is employed for purposes other than snow-ice control, for example, conveying gravel or pothole repair material, the lever  242  may be actuated to close the plate  178  (FIG. 6) to its position shown in phantom at  178 ′. Gate  60  will open to the same orientation shown in FIG. 3 to permit this supplemental use of the vehicle  10  without removal of the integrated version of the tailgate  60  described herein. As noted above, with the arrangement, the important capacity of the brine reservoir as represented at brine tanks  92 - 94  is doubled with this integrated configuration, that capacity permitting the utilization of less expensive sodium chloride salt-based brine with requisite modem mixing ratios selected to defeat the ice-pavement bond. As noted above, the capacity for the instant embodiment reaches about 140 gallons. For the noted alternate winter seasonal use of the vehicle  10  as incorporating tailgate assembly  60 , the broadcasting assembly  182  is pivoted upwardly and secured in position against the tailgate frame  62 . 
     FIG. 4 illustrates the performance of one version of the current (ODOT) approach employing a combinational tailgate assembly. An identical vehicle as represented at  10  in FIGS. 1-3 is represented in general at  50 . In view of this identity of general structure, identifying numeration for the truck components and associated bed which remain the same are provided with the same numeration as the other figure. The tailgate for utility vehicle  250  is represented generally at  252  and includes a tailgate frame represented generally at  254 . On upper sides of frame  254  there is weldably provided an upper support component one of which is represented at  256 . These components as at  256  extend to a hinge or pin connection with the “normal” pin retention bracket  48  and associated pin  52 . The oppositely disposed connection is identical. Rearwardly of the frame  254 , the tailgate  252  is configured having a transport mechanism chamber  258  of generally triangular cross section, the lower portion of which supports a bed transport mechanism implemented as an auger having a shaft  260  and a feed chamber  262 . A feed chute  264  supporting a disc or spinner assembly  266  pivots with the feed chamber  262  about the shaft  260 . Mounted upon the rearward surface  268  of transport mechanism  258  is a polymeric brine tank represented at  270 . Note that the tank  270  does not extend through the tailgate frame  254 . Mounted upon the outer surface of the middle one of the brine tank  270  is a hydraulic pump housing  272 . This arrangement provides for a brine storage capacity of about  70  gallons. When the vehicle  250  is in the dumping orientation represented in FIG. 4 which is the same orientation as shown in FIG. 3, the center of gravity of the thus mounted tailgate  252  may be represented as being present in a vertical plane represented by dashed line  274 . When the brine tank assembly  270  is essentially empty, the amount of tailgate opening will be as shown, for example, about 5½ inches. Where those brine tanks contain brine, the tailgate will not open. 
     Since certain changes can be made in the above-described apparatus and method without departing from the scope of the invention herein involved, it is intended that all matter contained in the above description or shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense.

Summary:
A dump bed highway maintenance vehicle is provided with a removable tailgate which is formed of a tailgate frame having a pivotal connection with the truck dump bed which is spaced rearwardly from a normal pivot connection and contains a brine tank assemblage extending through the frame above a cross-bed auger. By so extending the brine tank assemblage through the frame, the center of gravity of the pivot mounted tailgate resides in a vertical plane extending through the outwardly displaced frame pivot mechanism. The forward wall of the brine tank assemblage is slanted forwardly upwardly to define a cross section resembling an inverted truncated right triangle.