Patent Publication Number: US-6905281-B2

Title: Vehicular impact absorbing apparatus having cushion pins

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a safety guard installed on a roadway at which a vehicular impact is expected, and more particularly to a vehicular impact absorbing apparatus having cushion pins, which ensure effective arrest of vehicle impacts. 
     2. Description of the Prior Art 
     There are several general types of roadway safety facilities, including for example, guard rails for protecting vehicles from deviating from the road and median dividers for preventing intrusion of a vehicle into the opposite lane. Further, safety guards or crash cushions are installed alongside roadways in front of obstructions such as concrete walls, the ends of dividers, toll booths and the like for protecting them against vehicular impact as well as protecting passengers during a car crash. 
     The guard rail and the median divider seldom collide head-on with a vehicle as they are disposed along by the road. However, the safe guard is apt to collide head-on with vehicles since it is located infront of the driving direction of oncoming automobiles. 
     In the event of a head-on collision with the safe guard, enormous impact energy is applied to the vehicle which can result in a fatal blow to the vehicle and passenger. Therefore, it is desirable that the safe guard effectively absorbs kinetic energy of an impacting vehicle to minimize injury of passengers and to reduce damage to roadway facilities as well as the vehicle. 
     A common type of safety guard is formed by a concrete structure or a cushion using worn tires or polyurethane foam. The safety guard on a concrete structure may protect roadway facilities using a simple construction at low cost, however it does not function to absorb vehicular impacts at all. As a result, it presents a serious roadway hazard to vehicles. In the case of the cushion safety guard, it is good at absorbing impact energy, however it returns the impact energy as repulsive power which sends the impacting vehicle back into traffic at a steep angle. This may cause secondary collisions on the roadway with other vehicles. 
     To overcome these problems of the conventional safety guard, various vehicular impact absorbing apparatuseshave been proposed, for example, in Korean Patent No. 0348707, U.S. Pat. No. 5,868,521, and PCT International Publication No. WO 00/52267. 
     Korean Patent No. 0348707 discloses a vehicular impact absorbing apparatus having an array of rubber barrels filled with a cushioning material. The rubber barrels are supported by a steel plates buried in each barrel and slidably mounted on a single centered rail. The barrels following the front barrel are provided at an inner side thereof with a wave-shaped steel plate. The rear end of barrel array is fixed to a roadway obstruction by anchor bolts. In a crash, the barrels are retracted along the rail and compressively transformed to absorb the kinetic energy of an impacting vehicle. The wave-shaped steel plate restrains the repulsive force resulting from the impact energy. 
     However, since the cushioning simply depends on the physical transformation of the cushioning material, the cushioning effect may be affected by the characteristics of the cushioning material, and it is difficult to fully cushion several tons of kinetic energy. 
     Although this may be overcome by extending the length of the barrel array, it may be limited by conditions of the roadway. Further, since the barrel array is fixed to the concrete wall, it can not be installed at the location where concrete walls do not exist, such as the ends of median dividers and the front of simple branched roads. 
     U.S. Pat. No. 5,868,521 discloses a highway crash cushion including an array of diaphragms each of which has a guide slidably mounted on a single central guide rail, a plurality of energy absorbing elements disposed between the diaphragms, and an array of fender panels extending alongside the diaphragms. In axial collapse, the diaphragms move closer to one another, the fender panels telescope over one another, and the energy absorbing elements are compressed. Since this crash cushion also absorbs the kinetic energy of an impacting vehicle as the crash cushion collapses axially, it may require a considerable axial length of the crash cushion in order to absorb several hundred tons of kinetic energy. Also, it is costly to repair and rebuild the energy absorbing elements following a collision. 
     PCT Publication WO 00/52267 discloses a crash cushion formed by a pipe rack frame that retains a number of axially disposed cushion barrels. The pipe frame is provided with a slider which constrains the barrels. The barrels are crushed to absorb a vehicular impact. Using such a crash cushion, it is also difficult to fully absorb several tons of impact energy. 
     SUMMARY OF THE INVENTION 
     Accordingly, the present invention has been made keeping the above problems occurring in the prior art in mind. An object of the present invention is to provide a vehicular impact absorbing apparatus which can effectively absorb the kinetic energy of an impacting vehicle. 
     Another object of the present invention is to provide a vehicular impact absorbing apparatus which is free from the restraint of installation due to roadway conditions. 
     A further object of the present invention is to provide a vehicular impact absorbing apparatus which prevents an impacting vehicle from springing back due to the repulsive power thereof. 
     A further object of the present invention is to provide a vehicular impact absorbing apparatus which utilizes discarded resources as a cushion element thereby minimizing installation costs. 
     A further object of the present invention is to provide a vehicular impact absorbing apparatus which can be quickly rebuilt following a collision thereby reducing the cost to repair and rebuild the apparatus. 
     In order to accomplish the above objects, the present invention resides in a vehicular impact absorbing apparatus, which comprises: a tubular guide rail having a guide slit longitudinally formed at the upper part of the guide rail, the guide rail being fixed to the ground; a plurality of sliders movably mounted in the guide rail at predetermined intervals, the upper part of each slider being laid on the upper part of the guide rail through the guide slit; a plurality of cushion units mounted on the upper part of each slider, each cushion unit being elastically deformed by vehicular impacts to retract along the guide rail; a group of cushion pins mounted across the guide rail at predetermined intervals located between the sliders, the cushion pins being broken serially by the slider which is retracting rearward; a stopper installed around the rear end of the guide rail for stopping the retracting cushion units; and a side fence retractably mounted alongside the cushion units, the one end of the side fence being fixed to the stopper and the other to the front cushion unit. 
     In accordance with a preferred feature of this invention, the cushion unit includes a base plate mounted on the top portion of the slider, the base plate having supports fixed thereto and vertically extending along the side portion of the cushion unit; a cushion element loaded onto the supports of the base plate with a part of the cushion element protruding from the front and rear side of the base plate; and a holding cover coupled to the base plate and the top portion of the support, surrounding both sides of the cushion element. For example, the cushion element includes a stack of worn tires laid around the support. 
     In accordance with a preferred feature of this invention, the guide rail is formed with a plurality of fastening holes for receiving the cushion pins, and the fastening holesare formed in two rows such that the holes in each row cross each other. 
     In accordance with a preferred feature of this invention, the apparatus further comprises an outer cover for enclosing the components of the apparatus, the outer cover including a plurality of middle covers coupled to each cushion unit for covering the cushion units, a front cover coupled to the foremost middle cover for covering the front portion of the foremost cushion unit, and a rear cover for covering the stopper, the covers being coupled to telescope over one another. 
     Using the vehicular impact absorbing apparatus according to the present invention, an effective absorption of the kinetic energy of an impacting vehicle is possible through an elastic deformation of the cushion units and successive shear of the cushion pins. 
     Further, since the broken cushion pins interfere with the sliders after the sliders pass through the cushion pins, it is possible to prevent spring back of the cushion elements due to the repulsive power thereof and to stop the movement of the impacting vehicle. This contributes to a protection of the impacting vehicle againsta secondary collision with another vehicle. 
     Furthermore, since the amount of compressive deformation of the cushion elements is increased proceeding rearward, successive cushion and deceleration of the vehicular impact is possible, thereby absorbing the minute impact energy and minimizing the effect of the impact on vehicle passengers. 
     In addition, since the cushion units are elastically deformed as they move along the guide rails, the cushion units can be reused and only a simple replacing operation of the broken cushion pins is required. This contributes to reduction in maintenance and repair costs. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The above and other objects, features and advantages of the present invention will be more clearly understood from the following detailed description taken in conjunction with the accompanying drawings, in which: 
         FIG. 1  is a perspective view of a vehicular impact absorbing apparatus according to the present invention; 
         FIG. 2  is a partial exploded perspective view of the vehicular impact absorbing apparatus shown in  FIG. 1 , with its cover removed from the apparatus; 
         FIG. 3  is a cross-sectional view taken along line III—III of  FIG. 1 ; 
         FIG. 4  is a cross-sectional view taken along line IV—IV of  FIG. 3 ; 
         FIG. 5  is an exploded perspective view of a slide cushion unit extracted from the apparatus of the present invention; 
         FIG. 6  is a partial enlarged front view showing the assembled state of the slide cushion unit shown in  FIG. 5 ; 
         FIG. 7  is a partial cross-sectional view taken along line VII—VII of  FIG. 6 ; 
         FIG. 8  is an exploded perspective view of a cover assembly of the vehicular impact absorbing apparatus of  FIG. 1 ; 
         FIGS. 9A  to  9 C are side views schematically illustrating the cushioning operation of the apparatus according to the present invention; 
         FIGS. 10A and 10B  are partial plan sectional views showing the energy absorbing operation of the slide cushion unit of this invention; 
         FIG. 11  is a cross-sectional view of a vehicular impact absorbing apparatus according to another embodiment of the present invention; and 
         FIGS. 12A and 12B  are plan views schematically showing an example of installation of the vehicular impact absorbing apparatus according to the present invention, each of which are installed in front of a branch road and at an end of a median divider, respectively. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     This invention will be described in further detail by way of exemplary embodiments with reference to the accompanying drawings. 
     Referring to  FIG. 1 , there is shown a safety guard including a vehicular impact absorbing apparatus according to the present invention. The impact absorbing apparatus is covered with a cover assembly  70 , which includes a front cover  72 , a middle cover  71 , and a rear cover  73 . The covers  71 ,  72  and  73  are adapted to telescope over one another in an axial collapse. The details of the cover assembly  70  will be described hereinafter with reference to FIG.  8 . 
     As shown in  FIGS. 2 and 4 , the vehicular impact absorbing apparatus includes a plurality of cushion units  30  arranged in the form of an array. The cushion units  30  are to absorb vehicular impacts in a more effective way. Each cushion unit  30  has a slider  20  movably mounted onto a guide rail  10 , which is fixed to the ground. The guide rail  10  is provided with a group of cushion pins  40  fixed across the guide rail  10 . Each group of cushion pins  40  is disposed at a predetermined interval along the guide rail  10 . The apparatus further includes a stopper  50  provided at the rear end of the guide rail  10  and a pair of side fences  60  provided alongside the cushion units  30 . The side fence  60  is comprised of a plurality of retractable bars  61 . 
     The guide rail  10  is formed by a hollow rectangular metal tube and is provided at its upper center surface with a guide slit  11  formed along the length thereof. Also, the guide rail  10  has a plurality of mounting plates  12  provided along both sides thereof at intervals so as to fix the guide rail  10  on the ground “R” by anchor bolts  13 . 
     Further, the guide rail  10  is formed with a plurality of fastening holes  14  for receiving the cushion pins  40 . The fastening holes  14  are formed in two rows such that the holes  14  in each row cross each other. This will allow the cushion pins  40  to be densely disposed within the designated section of the guide rail  10 . 
     Preferably, each cushion pin  40  consists of a bolt  41  and a nut  42 . The number of cushion pins  40  as well as their diameter is determined by considering the amount of expected impact energy and allowable shearing stress of the material. 
     Preferably, as shown in detail in  FIG. 5 , the guide rail  10  is manufactured from a pair of channel-type steel frames  15  in such a way that the frames  15  face each other with a desired space and are fixed to the mounting plates  12  by a welding process. 
     Preferably, as shown in  FIG. 4 , the guide rail  10  is provided in parallel pairs having a desired interval, so that they stably support the cushion units  30  thereon and double the amount of cushion pins  40  being provided in the guide rail  10 . With this, the cushion effect is increased enough to reduce the size of the cushion unit array to almost half of its longitudinal length, as compared to the one without the cushion pins  40 . 
     Inside the guide rail  10 , the slider  20  is movably mounted at predetermined intervals. As apparent in  FIGS. 5  to  7 , the slider  20  is formed into an I-beam member having a web  21  and a pair of flanges  22 ,  23  formed at upper and lower ends of the web  21 . The web  21  of the slider  20  is inserted into the guide slit  11  of the rail  10 , with the upper flange  22  being placed over the outer side of the guide rail  10 . 
     Referring to  FIGS. 6 and 7 , the slider  20  is provided at its front and rear portion with a pair of anti-shaking members  24  which pass through the web  21  of the slider  20 . The top portion of each anti-shaking member  24  abuts against the inner top surface of the guide rail  10 . 
     The anti-shaking member  24  is preferably made from a bolt and nut. However, the anti-shaking member  24  may have other forms, for example, a pin, a roller and so on. 
     The anti-shaking member  24  prevents up-and-down movement of the slider  20  when a vehicular impact is applied to the cushion unit  30 . 
     Referring again to  FIG. 6 , there is shown a pair of bolt heads  39   a  placed between the lower sides of the upper flange  22  of the slider  20  and the upper surface of the guide rail  10 . The bolt  39  couples the slider  20  to the cushion unit  30 . 
     The cushion unit  30  includes a base plate  31  mounted on the top portion of the sliders  20 , a pair of supports  32  fixed to the base plate  31  and vertically extending along the side portion of the cushion unit  30 , a cushion element  33  loaded onto the base plate  31 , a holding cover  34  for holding the cushion element  33  in the base plate  31 . 
     The base plate  31  is formed into a rectangular steel plate, with its corner portion being laid and fixed to the upper flange  22  of the slider  20  by bolts  39   a  and nuts  39   b  (See FIG.  5 ). The axial length of the base plate  31  is determined such that a part of the cushion element  33  protrudes from both edges of the base plate  31 . 
     Preferably, a reinforcing plate  31   a  is interposed between the lower side of the base plate  31  and the upper flange  22  of two sliders  20 . Thus, the bolt head  39   a  fixed to the upper flange  22  of slider  20  can be in contact with the upper surface of the guide rail  10 . 
     A pair of vertical supports  32  is placed on both sides of the base plate  31 , for supporting the cushion element  33 . The support  32  is formed by X-shaped crossing plates  32   a  having a desired longitudinal length. The end of each plate  32   a  is formed with a bending portion  32   b , for reinforcing the strength thereof. The support  32  may have other appropriate forms to receive the cushion element  33 . 
     The cushion element  33  is preferably formed by a stack of worn tires  33   a  placed around the support  32 . The cushion element  33  can be made of a resilient material such as rubber, polyurethane and the like. However, worn tire prevails over other materials because it has excellent elasticity and is a useful recyclable material. 
     The holding cover  34  is comprised of a pair of channel-shaped unit covers  35  and a coupling plate  36 . The holding cover  34  is fixed to both sides of the base plate  31  such that the cover  34  partly surrounds the cushion element  33  while a part of the front and rear portion of the cushion element protrude therefrom. The coupling plate  36  connects an upper portion  35   a  of the unit cover  35  to the opposing coupling plate. The lower portion  35   b  of each unit cover  35  is placed between the base plate  31  and the reinforcing plate  31   a  to be joined thereto by the bolt  39   a  and nut  39   b . Also, the upper portion  35   a  of each unit cover  35  is coupled to the coupling plate  36  and then the base plate  31  by a stay bolt  37 , which is passed through one compartment of each support  32 . 
     As can be seen in  FIG. 5 , one end of the stay bolt  37  is fixed to the base plate  31  and the other end to the coupling plate  36 . With this arrangement, the cushion element  33  can be stably supported by the holding cover  34 . Instead of the stay bolt  37  which crosses the support  32 , a short bolt can be integrally formed at the top and bottom portions of the support  32  by welding. 
     Particularly, the upper portion  35   a  of each unit cover  35  is sized such that its width is shorter than that of the lower portion  35   b  thereof, so that the exposed area of the cushion element  33  around the upper portion  35   a  of unit cover  35  is is sized such that its width is shorter than that of the lower portion  35   b  thereof, so that the exposed area of the cushion element  33  around the upper portion  35   a  of unit cover  35  is larger than that of the lower portion  35   b . This allows the cushion element  33  to have a margin for absorbing more impacts when all of the cushion units  30  are compressed to face each other by a vehicular impact. 
     At the side portion  35   c  of the unit holding cover  35 , a plurality of guide tunnels  38  are horizontally provided to movably insert a side bar  61  of the side fence  60 , which will be described hereinafter. Further, the upper and lower outlines of the guide tunnels  38 , and brackets  38   a ,  38   b  are provided to support the outer cover  70 . 
     The upper guide tunnels  38  and brackets  38   a ,  38   b  can be made in the form of a separate unit and then fixed to the side portion  35   c  of the unit cover  35  by welding. Also, they can be formed into a corrugated integral assembly and welded to the side portion  35   c.    
     As shown in  FIG. 7 , a group of cushion pins  40  are mounted to the guide rail  10  such that they are disposed at a predetermined interval alongside the guide rail  10 . The cushion pins  40  are arranged in two rows, corresponding to the fastening holes  14  formed in the guide rail  10 . As mentioned before, the cushion pins  40  in each row are placed to cross each other. This allows the cushion pins  40  to be densely disposed in the designated section of the guide rail  10 . Every group of cushion pins  40  serially cushion vehicular impacts as the cushion units  30  collapse axially. 
     Referring to  FIG. 3 , the widths b 1 , b 2 , . . . b 5  of each holding cover  34  are determined such that they are gradually decreased proceeding in the rearward direction (b 1 &gt;b 2 &gt;b 3 &gt;b 4 &gt;b 5 ). This provides for a sufficient installing space for a group of cushion pins  40  and reduced total length of the cushion unit array. As a result, the safety guard can be adequately installed in a limited area such as a ‘safety zone’ which is in front of a roadway branch, for example. 
     Accordingly, the size of the exposed portions of each cushion element  33  is increased as they proceed in the rearward direction, which allows cushion element  33  to have an increased amount of elastic deformation. This contributes to a smooth absorption of the kinetic energy of an impacting vehicle and minimizes shock for the passenger. 
     Also, because the kinetic energy of an impacting vehicle is decreased as it proceeds in the rearward direction, it has been determined that the spaces S 1 , S 2 , . . . S 4  between each cushion unit  30  may gradually decrease as they proceed in the rearward direction (S 1 &gt;S 2 &gt;S 3 &gt;S 4 ), and the number of the cushion pins  40  may decrease as well. As a result, the total length of the cushion unit array can be reduced. 
     On the other hand, the front cushion unit  30   a  is comprised of two cushion units  30 , incorporated into a unit body. This is because the front cushion unit  30   a  will receive the maximum kinetic energy at the initial vehicular impact. This allows for a stable resistance to the initial impact and a smooth intrusion into the subsequent cushion unit. 
     Behind the last cushion unit, the stopper  50  is provided to limit the rearward movement of the cushion unit array. The stopper  50  is preferably formed into a truss type steel structure. As shown in  FIG. 2 , the stopper  50  includes a pair of vertical posts  51  which are supported by a slant support bar  52 , respectively. A pair of connecting bars  53  are horizontally joined between the support bars  52 . The post  51  and the slant support bar  52  are fixed to the ground by an anchor bolt  54 . 
     Referring again to  FIG. 2 , the side fence  60  is comprised of a plurality of side bars  61  horizontally disposed between the front cushion unit  30   a  and the stopper  50 . The side fence  60  is provided to cushion a lateral vehicular impact, which prevents the impacting vehicle from moving into the region between the cushion units  30  and, acting like a guard rail, redirects the impacting vehicle without sending it back into traffic. 
     In an axial vehicular impact, the side bars  61  should be compressed alongside the cushion units  30  moving rearward. To this end, each side bar  61  consists of three separate bars  62 ,  63  and  64 , coupled to one another in a telescopic form. The side bar  61  is inserted into the guide tunnels  38  provided at each side portion of the holding covers  34 . Each of the front separate bars  62  is fixed to a vertical coupling bar  65  provided at both sides of the guide tunnel  38  of the front cushion unit  30   a , by a bolt  67 . Further, each of the rear separate bars  64  is fixed to the vertical post  51  of the stopper  50  by a bolt  66 . 
     In such a side bar  61 , the length of the rear separate bar  64  corresponds to the length of the cushion unit assembly, from the post  52  of the stopper to the front cushion unit  30 , that is fully compressed by an axial vehicular impact. This will prevent the side bar  61  from intruding into the impacting vehicle. 
     Referring to  FIG. 8 , the vehicular impact absorbing apparatus of this invention preferably includes an outer cover  70 , which can be compressed simultaneously with the cushion units  30  and allows for good appearance of the safety guard. The outer cover  70  consists of a plurality of middle covers  71  for covering the cushion unit array, a front cover  72 , and a rear cover  73  for covering the stopper  50 . These covers are coupled to telescope over one another, so that each unit of middle cover  71  can be overlapped successively and retracted to the rearward middle cover. To this end, each of the middle covers  71  is fixed to the bracket  38   a  of the corresponding cushion unit  30  by a screw  74 , and the front cover  72  is fixed to the front middle cover. The rear cover  73  is also fixed to the rearward middle cover by screws. In this embodiment, the middle cover  71  is horizontally divided into at least two panels  71   a ,  71   b  which acts as a fender panel. To couple the divided panels to each other, one of the panels  71   a ,  71   b  is provided at the top end part thereof with a rise portion  75 , on which the other top end part is fitted. The panels  71   a ,  71   b  are coupled to each other by screws  76 . 
     Further, a guide bead  77  is outwardly formed at the upper portion of the middle cover  71  to secure a space for the top end of the stay bolt  37 . Also, a plurality of reinforcing beads  78  are outwardly formed at each side of the middle cover  71 . 
     The surface of the front cover  72  is attached with a safety sign  72   a , preferably made of a light-reflective material. The rear cover  73  is provided at its center portion with a door  73   a  for communicating with a box “B” placed on the space of the stopper  50 . The box “B” receives for example sand bags and the like. 
     The outer cover or cover assembly  70  may be manufactured from high strength synthetic resins, such as fiber glass reinforced plastics (FRP). 
     The operation of the above vehicular impact absorbing apparatus will be described with reference to  FIG. 9A  to FIG.  10 B. The vehicular impact absorbing apparatus of this invention is installed on a site as shown in FIG.  3 . The cushion units  30  are positioned maintaining a predetermined space S 1 , S 2 , S 3  and S 4  relative to each other. The side bar  61  and the outer cover  70  are at their fully extended state. 
     In this state, when the front of the cover assembly  70  collides with a vehicle “V”, as shown in  FIG. 9A , the foremost cushion unit  30   a  is tilted rearward (shown as imaginary lines) and the exposed portion of the cushion element  33  is elastically deformed to absorb the initial vehicular impact, which is considered the largest kinetic energy of the impact. 
     At the same time, as the foremost cushion unit  30   a  moves rearward by the remaining kinetic energy, the sliders  20  joined to the bottom portion of the cushion unit  30   a  begin to move quickly in the rearward direction. 
     As the sliders  20  move rearward along the guide rail  10 , the cushion pins  40  mounted over the designated space between the foremost cushion unit  30   a  and the subsequent cushion unit  30  will be broken one by one, by colliding with the web  21  of the slider  20 , as shown in  FIGS. 10A and 10B . 
     The cushion pins  40  will resist against the striking force of the slider  20  due to its impact strength, and finally be broken. This process contributes to a smooth absorption operation of the present invention. Furthermore, since the cushion pins  40  are mounted in a group at every location between the subsequent cushion units  30 , the kinetic energy of the impacting vehicle will gradually decrease due to breaking of the cushion pins  40 . 
     Thus, kinetic energy can be absorbed by a group of cushion pins  40  and the speed of the impacting vehicle will decrease. 
     As shown in  FIG. 9   b , as the foremost cushion unit  30   a  moves to the subsequent cushion unit  30  while breaking the cushion pins  40  located at the front area, the exposed cushion element  33  of the cushion unit  30  is also elastically deformed by the successive vehicular impact. This cushion unit  30  also begins to move quickly in the rearward direction along the guide rail  10 . Accordingly, the cushion pins  40  mounted over the designated space between the subsequent cushion units  30  will be broken serially with a resistance against the strike of the second slider. With this, the kinetic energy of the impacting vehicle and the speed of the impacting vehicle is further decreased. 
     Lastly, as shown in  FIG. 9C , as all the cushion units  30  move closer to the rear end portion of the cushion unit array, the movement of cushion units  30  are restrained by the stopper  50  with each cushion unit  30  being closer to one another in the elastically deformed state. Thus, the kinetic energy of the impacting vehicle is eliminated and the impacting vehicle is stopped. 
     In this operation, since the widths b 1 , b 2 , . . . b 5  of each holding cover  34  of the cushion units  30  are gradually decreased and the exposed portions of the cushion elements  33  are gradually increased as they proceed in the rearward direction, the amount of compress deformation of the cushion elements  33  increases as the kinetic energy of an impacting vehicle and the vehicle speed decrease, by successive cushioning and deceleration of the vehicular impact, thereby effectively absorbing the minute impact energy and minimizing the effect of the impact on the passenger. 
     Further, since the upper portion  35   a  of the unit holding cover  35  is shorter in width than the lower portion  35   b  thereof, and the exposed area of the cushion element  33  around the upper portion  35   a  is larger than that of the lower portion  35   b , the cushion element  33  can be further compressed in the full retraction state of the cushion units  30 , thereby absorbing a marginal impact energy. 
     Therefore, according this embodiment, the kinetic energy of the impacting vehicle can be nearly removed at the time all the cushion units  30  are moved to the rear end and are halted by the stopper  50 . This will minimize injury of passengers and reduce damage of the impact absorbing apparatus itself as well as the impacting vehicle. 
     Particularly, since a group of cushion pins  40 , disposed at short intervals within a designated section, are broken upon the strike of the slider  20 , the broken cushion pins  40  interfere with the sliders  20  after passing through the cushion pins. Therefore, it is possible to prevent spring back of the cushion elements  33  due to the repulsive power thereof and to stop the impacting vehicle. This will protect the impacting vehicle against secondary collision with another vehicle. 
     Further, since the cushion units  30  are elastically deformed with the cushion elements  33  as they move along the guide rail  10 , the cushion units  30  may be reused after replacing the broken cushion pins  40 . This will contribute to saving costs for maintenance and repair. 
       FIG. 11  shows a vehicular impact absorbing apparatus according to another embodiment of this invention. 
     In this embodiment, a cushion unit  30  has only one cushion element  33 , which consists of a stack of worn tires like the previous embodiment. Thus, the width of the cushion units is narrower (almost half) than that of the previous embodiment. This arrangement can be applied to the location where the vehicle speed is restricted to a low speed and the kinetic energy of the impacting vehicle is relatively small. The rest of the components of this embodiment are the same as those of the first embodiment. Therefore, the detailed description will be omitted for brevity&#39;s sake, denoting the same reference numerals of the same components described in the first embodiment. 
       FIG. 12A  shows an example of an installation of the vehicular impact absorbing apparatus according to this invention. The safety guard “C” includes the above impact absorbing apparatus, which is installed in front of a branch road. 
       FIG. 12B  shows the invention installed in front of an end of a median divider “W” , between both ends of the guide rails to constitute a part of the median divider “W”. In this case, H-beams fixed adjacent to each end of the guide rails may be used as a stopper. 
     As described above, according to the vehicular impact absorbing apparatus of this invention, it is possible to effectively absorb kinetic energy of an impacting vehicle through elastic deformation of the cushion units and successive shear of the cushion pins. 
     Further, since the broken cushion pins interfere with the sliders after passing through the cushion pins, it is possible to prevent spring back of the cushion elements due to the repulsive power thereof and to stop the impacting vehicle, thereby protecting the impacting vehicle against secondary collision with another vehicle. 
     Furthermore, since the amount of compress deformation of the cushion elements is increased proceeding rearward, a successive cushion and deceleration of the vehicular impact is possible, thereby absorbing the minute impact energy and minimizing the effect of the impact on the passenger. 
     Further, since the cushion units are elastically deformed as they move along the guide rails, the cushion units can be reused and only replacement of the broken cushion pins is required. This contributes to reduction in maintenance and repair costs. In addition, the above allows for a reduced total length of the cushion unit array and the safety guard can be properly installed in a limited area. 
     Further, since worn tires are used as the cushion element of each cushion unit, the cost for manufacturing and repair can be reduced. After collision, the broken parts, for example the cushion pins, can be simply replaced, which contributes to saving costs for maintenance and repair. 
     Although preferred embodiments of the present invention have been described for illustrative purposes, those skilled in the art will appreciate that various modifications, additions and substitutions are possible, without departing from the scope and spirit of the invention as defined in the accompanying claims.