Abstract:
An energy absorbing system having a stanchion, a linearly extendable energy absorber coupled to the stanchion, a net coupled to the energy absorber, wherein the net transfers force to the energy absorber, and a securing mechanism that maintains tension between the net and the energy absorber until acted upon by tensile forces of at least a minimum threshold force, wherein at least a portion of the system is retractable into the ground.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of Ser. No. 10/504,068, entitled “Energy Absorbing System”, filed Aug. 10, 2005, issued as U.S. Pat. No. 7,785,031, which is the national stage filing of PCT/US03/03586, entitled “Energy Absorbing System”, filed Feb. 6, 2003, which claims priority from U.S. Non-provisional application Ser. No. 10/359,666, now U.S. Pat. No. 6,843,613, entitled “Energy Absorbing System”, filed Feb. 6, 2003, which claims priority from U.S. Provisional Application Ser. No. 60/421,144, entitled “Energy Absorbing System”, filed on Feb. 7, 2002 and converted to a provisional application on Feb. 5, 2003. International Application No. PCT/US03/03586 also claims priority from U.S. Provisional Application Ser. No. 60/421,144 filed on Feb. 7, 2002. 
    
    
     BACKGROUND OF THE INVENTION 
     This invention relates to an energy absorbing system that can be used to dissipate unwanted energy such as, e.g., the energy of an errant vehicle. The system can be used in a variety of applications, including HOV lane traffic control, drawbridges, security gates, or crash cushion applications. In one application, the system is used to prevent a vehicle from crossing a railroad track while the warning gates are down or there is a train in the area. 
     The problem of vehicles improperly crossing railroad tracks is becoming more pronounced due to a rise in both the average speed of trains and in the number of vehicles on the roads. For example, a new high speed rail line has recently been put into service on the east coast of the United States, which passes through densely populated areas. Traditional systems for preventing vehicles from crossing the tracks at inopportune times have proved less than fully satisfactory. Traditional gates can be bypassed by impatient drivers who don&#39;t yet see a train coming, and, in any event, will not stop a vehicle that is out of control. 
     Other vehicle barriers have been proposed, but none have solved the problem in a manner that is both feasible and commercially practical. Thus, old-fashioned gates are still the most common system for protecting railroad crossings. 
     SUMMARY OF THE INVENTION 
     In one aspect, an energy absorbing system according to the present invention includes a stanchion, a bearing sleeve rotatable around the stanchion, one or more hydraulic shock absorbers in its compressed state connected to the sleeve, a threshold force securing mechanism connected to the shock absorbers, and a ground retractable restraining net connected to the shock absorbers, wherein the securing mechanism prevents expansion of the shock absorbers until acted upon by tensile forces of at least a minimum threshold force, wherein the minimum threshold force exceeds a static tensile force exerted by the restraining net in a quiescent state upon the shock absorber, and wherein the minimum threshold force is less than dynamic tensile forces that the net would exert on the shock absorber when an automobile collides with the net at substantial speed. 
     In another aspect, an energy absorbing system according to the present invention includes a fixing means for fixing a vertical axis, a shock absorbing means connected to the fixing means, for absorbing tensile forces while rotating around the vertical axis, and a threshold force securing means connected to the shock absorbing means, for preventing expansion of the shock absorbing means until acted upon by tensile forces of at least a minimum threshold force. Preferably, the shock absorbing means is connected to a rotating means for rotating about the fixing means and/or axis. The rotating means may he a bearing sleeve, for example. The energy absorbing system may further comprise a torque protection means for adding structural strength to the shock absorbing means to resist deformation due to the torque upon the shock absorbing means. A restraining means may be connected to the shock absorbing means, for absorbing forces and for transferring forces to the shock absorbing means, and through the shock absorbing means to the support means. The restraining means may include a restraining net or net means. It preferably comprises horseshoe cable, or cable extending substantially horizontally in a wave pattern with vertical amplitude, having peaks, valleys and midpoints, wherein tangents of the wave midpoints are at least 90 degrees from tangents of the peaks and valleys. 
     In yet another aspect, an energy absorbing system according to the present invention includes a stanchion, a bearing sleeve rotatable and optionally vertically slidable on the stanchion, a shock absorber connected to the sleeve, and a shear pin connected to the shock absorber which prevents expansion of the shock absorber until acted upon by tensile forces of at least a minimum threshold force. Preferably, the minimum threshold force is about 3,000 to about 15,000 pounds. Most preferably, the minimum threshold force is about 5,000 to about 10,000 pounds. The energy absorbing system may include wheels and a cross-bar between at least two shock absorbers on a stanchion, supporting the shock absorbers. 
     In a further aspect, an energy absorbing system according to the present invention includes a stanchion, a bearing sleeve rotatable and optionally vertically slidable on the stanchion, a shock absorber connected to the sleeve, a restraining net connected to the shock absorber, and a shear pin connected to the shock absorber which prevents expansion of the shock absorber until acted upon by tensile forces of at least a minimum threshold force. Preferably, the restraining net in a quiescent state exerts a static tensile force upon the shock absorber, and the minimum threshold force exceeds the static tensile force. The net preferably extends across a roadway and is ground retractable. The net preferably comprises horseshoe cable, or cable extending substantially horizontally in a wave pattern with vertical amplitude, having peaks, valleys and midpoints, wherein tangents of the wave midpoints are at least 90 degrees from tangents of the peaks and valleys. 
     In a still further aspect, a restraining net according to the present invention includes top, middle and bottom horizontally extending structural cables, and horseshoe cable extending along and between the horizontally extending cables, or cable extending substantially horizontally along the horizontally extending structural cables in a wave pattern with vertical amplitude, having peaks, valleys and midpoints, wherein tangents of the wave midpoints are at least 90 degrees from tangents of the peaks and valleys. 
     In yet another aspect, a railroad crossing safety system according to the present invention includes a roadway, railroad tracks crossing the roadway, first and second energy absorbing systems installed respectively on each side of the roadway, ground retractable restraining means for restraining automobiles from crossing the railroad tracks, the restraining means extending across the roadway between the first and second energy absorbing systems on each side of the railroad tracks, each of the first and second energy absorbing systems comprising supporting means for providing a rigid support for a fixing means, fixing means for rigidly fixing a vertical axis relative to the supporting means, shock absorbing means for absorbing forces applied to the shock absorbing system, the shock absorbing means being mounted on the fixing means to rotate around the vertical axis, and a threshold force securing mechanism connected to the shock absorber preventing expansion of the shock absorber until acted upon by tensile forces of at least a minimum threshold force, wherein the restraining means comprises horseshoe cable. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1A  is a perspective view which illustrates a railroad crossing for a multi-lane roadway with one embodiment of the invention installed and restraining an automobile; 
         FIG. 1B  is a perspective view which illustrates a railroad crossing for a multi-lane roadway with a preferred embodiment installed and restraining an automobile; 
         FIG. 2A  is a top view, partially cut away, of an embodiment as it would appear on one side of the railroad track; 
         FIG. 2B  is a side view, partially in section, of a net slot, a bunker, a net, a stanchion, and a net raising and lowering mechanism, which includes a pair of hydraulic shock absorbers with threshold force securing mechanism, with wheels and a vertical cross-bar to support the shock absorbers; 
         FIG. 2C  is a side view, partially in section, of a net slot, a bunker, a net, a stanchion, and a net raising and lowering mechanism, which includes a pair of hydraulic shock absorbers with threshold force securing mechanism, without wheels and a vertical cross-bar to support the shock absorbers; 
         FIG. 3A  is a top view of a second embodiment as it would appear on one side of the railroad track; 
         FIG. 3B  is a side view of a second embodiment as it would appear on one side of the railroad track, with wheels and a vertical cross-bar to support the shock absorbers; 
         FIG. 3C  is a side view of a second embodiment as it would appear on one side of the railroad track, without wheels and a vertical cross-bar to support the shock absorbers; 
         FIG. 4A  is a sectional view of a stanchion with sleeve and net raising and lowering jacks; 
         FIG. 4B  is a side view of a stanchion with sleeve and net raising and lowering jacks; 
         FIG. 5  is an exploded, perspective view of a stanchion with sleeve and shock absorbers with threshold force securing mechanism; 
         FIG. 6A  is a side view of a preferred embodiment of a hydraulic shock absorber with shear pins to act as threshold force securing mechanism, shown partially cut away and in its quiescent state; 
         FIG. 6B  is a side view of a preferred embodiment of a hydraulic shock absorber with shear pins to act as threshold force securing mechanism, shown partially cut away and in its expanded state after a vehicular collision with the net; 
         FIG. 7A  is a side view of a second preferred embodiment of a hydraulic shock absorber with shear pins to act as threshold force securing mechanism and a torque protection structure, shown partially cut away and in its quiescent state; 
         FIG. 7B  is a side view of a second preferred embodiment of a hydraulic shock absorber with shear pins to act as threshold force securing mechanism and a torque protection structure, shown partially cut away and in its expanded state after a vehicular collision with the net; and 
         FIG. 8  is an expanded side view of a net according to one embodiment. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The energy absorbing system in one aspect of a preferred embodiment comprises a stanchion or other mechanism for providing a fixed vertical axis, shock absorbing mechanisms mounted on the stanchion for absorbing forces, and a restraining net or other barrier connected to the shock absorbing mechanism. The shock absorbing mechanism is preferably mounted for rotation about the axis and is expandable in a direction substantially orthogonal to the axis. 
     Preferably, the shock absorbing mechanism is a hydraulic shock absorber with a securing mechanism such that the piston does not expand except in response to tensile forces that meet or exceed a minimum threshold force. In one aspect, it is envisioned that static tension from the restraining net in its quiescent state would not exceed this minimum threshold force, but that increased tension due to the dynamic tensile forces exerted upon the shock absorber from an automobile driving into the restraining net would exceed this minimum threshold force. 
     In accordance with other embodiments, a restraining net comprises top, middle and bottom horizontally extending structural cables. Cable arranged in horseshoe-curves extends along and among the horizontally extending cables. The term “horseshoe-curve” includes a curve in the form of a wave with a plurality of horseshoe-shaped peaks and a plurality of horseshoe-shaped valleys. It has been found that such cable has improved capturing ability. In preferred embodiments, this cable extends substantially horizontally in a wave pattern with vertical amplitude (similar to a sine wave), having peaks, valleys and midpoints, wherein tangents of the wave midpoints are at least 90 degrees from tangents of the peaks and valleys, as is explained further below. 
     Referring to the drawings, wherein like reference numerals represent identical or corresponding parts through out the several views, and more particularly to  FIG. 1 , a general layout of an embodiment is shown installed at a typical railroad crossing. A roadway is indicated generally by reference numeral  10  and railroad tracks are indicated generally by reference numeral  12 . A pair of capture nets  20  are stretched across roadway  10  parallel to tracks  12 . Each capture net  20  extends between a pair of housings  22  located on opposite sides of roadway  10 . The net  20  is connected at each end to shock absorbers which in turn are connected to, or may be considered part of, mechanisms for raising and lowering nets  20 , as described in greater detail hereinafter. The mechanisms may be entirely contained in the housings. Alternatively, the mechanisms may protrude from the housings as shown in  FIG. 1 . Alternatively, the housings maybe omitted altogether. The mechanisms are under the control of a standard train-detecting system, such as is commonly used to control gates at railroad crossings. Each housing  22  covers a support  28  which provides support and stability. 
     Preferably, each net  20  is normally stored in a slot  24  that extends transversely across roadway  10  between housings  22 . Shown at the top of  FIG. 1  is a vehicle  26  which has crashed into net  20  and is restrained by net  20  to prevent it and its occupants from encroaching onto tracks  12  when the train passes through. Top net  20  has been deflected by the collision from its quiescent state so as to form a shallow “V” shape. The ability to be deflected, yet provide a restraining force, allows vehicle  26  to be progressively stopped, thereby lessening adverse effects of the impact forces acting on vehicle  26  and its occupants. The deflecting and restraining functions are achieved by a unique energy absorbing system, to be described in greater detail herein after. 
     A top view is shown in  FIG. 2A  with roadway  10  and housings  22  removed.  FIG. 2B  shows a side view along the lines  2 B- 2 B of  FIG. 2A .  FIG. 2C  shows a similar view. Support  28  comprises a concrete bunker  30  and a stanchion  32 . Stanchion  32  is a structure for rigidly fixing vertical axis  52 . Bunker  30  may be poured at the site, or it may be fabricated elsewhere and installed at the site, on each side of roadway  10  and comprises a foundation  34  and upstanding bunker walls  36 . Walls  36  define in bunker  30  a pit  38  which is open upwardly toward roadway  10 . Foundation  34  may typically, for example, be from two to twelve feet wide and from three to nine feet deep. The top  40  of walls  36  are preferably about six inches above ground level  42  to provide a protective curb around bunker  30 . A sump pump  44  is preferably provided to remove any water which might accumulate in pit  38  into a drainage pipe  46 . 
     Stanchion  32 , which may comprise a twenty-five inch steel pipe  48 , is filled with concrete  50  and is preferably embedded approximately four feet deep in foundation  34  at the bottom of pit  38  and extends five to six feet above the top of foundation  34 . Stanchion  32  has a vertical axis  52 , whose function will become clear hereinafter. Foundation  34  and wails  36  may be of solid concrete. Because of the size and mass of the support  28 , it provides a solid support which resists forces imposed upon it. 
     Also typically at the site is a concrete roadway foundation  54  which extends across roadway  10  to another bunker  30 , not described in detail, since all bunkers  30  may be identical. Roadway foundation  54  preferably includes at least one key slot  56  which comprises a recess of any convenient size and shape. 
     Roadway foundation  54  supports a pair of pre-cast, concrete structures  58 ,  58 ′ which comprise the net slots  24 ,  24 ′ in the roadway into which net  20  is lowered for storage. As shown in  FIGS. 2B and 2C , the top  60  of net slots  24 ,  24 ′ are at ground level  42 , so that they are flush with the surface of roadway  10 . Structures  58 ,  58 ′ form essentially a pair of net slots  24 ,  24 ′ which are shown end to end in  FIGS. 2A  Each of structures  58 ,  58 ′ are substantially U-shaped having a base  62 ,  62 ′ and a pair of upstanding arms  64 ,  64 ′ defining slots  24 ,  24 ′. Inasmuch as concrete structures  58  and  58 ′ are mirror images, otherwise being identical, the following explanation of structure  58  is also applicable to  58 ′. An example net slot  24  is shown in cross-sectional view in FIG. 8 of U.S. Pat. No. 5,762,443 to Gelfand et al., incorporated herein by reference. 
     The partial cross-section shown in  FIGS. 2B and 2C  bisects slot  24  and pit  38 . The upper surface of base  62  slopes toward pit  38  to permit runoff from accumulating in slot  24 , where it might freeze and cause an obstruction. Note that the slopes shown in  FIGS. 2B and 2C  may be decreased. The concrete structures  58  that form net slots  24  may be pre-cast elsewhere and then transported to the site. Base  62  of net slot  24  preferably has at least one downwardly extending key  66  which is of a complementary size and shape to key slot  56 . Key  66  aids in aligning the system with roadway foundation  54  and resists any shearing movement of concrete structure  58  relative to roadway foundation  54 . After key  66  has been fit into key slot  56 , key slot  56  is preferably grouted solid. Pre-casting the concrete structure  58  and providing it with key  66  simplifies the construction at the site, thereby reducing construction costs. 
     As shown in  FIGS. 2B and 2C , respectively, the energy absorbing system may be provided with or without wheels  80  and a vertical cross-bar  82  between the shock absorbers to support the shock absorbers. The cross-bar may also alleviate vertical torque on the shock absorbers, which might otherwise occur due to the fact that a vehicle colliding with the net causes the top and bottom cables (and therefore the shock absorbers) to tend to squeeze together. Thus, the cross-bar may act as a stabilizer against this vertical torque. The wheels  80  and cross-bar  82  are particularly preferred when the shock absorbers  84  are long and/or heavy. Although the wheels  80  and cross-bar  82  are shown in the net configuration comprising horseshoe cable, it is understood that they may be employed in other net configurations, including the configuration shown in  FIG. 1A . In addition, one may readily appreciate that skid plates or other supporting means may be used in combination with, or as a replacement for the wheels. 
     Referring to  FIGS. 4 ,  5 ,  6  and  7 , a preferred embodiment of the energy absorbing system comprises a bearing sleeve  72  which is rotatable and vertically slidable on stanchion  32 , and a pair of shock absorbers  84  mounted on bearing sleeve  72  by securing shock absorber flange  114  to bearing sleeve flange  116 . The shock absorbers  84  are equipped with a threshold force securing mechanism, as described in more detail below. 
     Stanchion  32  is embedded in foundation  34 , thereby rigidly fixing in concrete the location of vertical axis  52 . Slidable vertically on stanchion  32  is bearing sleeve  72 . Preferably, as seen in  FIGS. 4 and 5 , bearing sleeve  72  comprises a galvanized steel sleeve  74  with a lubrite bronze insert  76  press fit therewithin which is reamed to fit externally milled stanchion  32 . In  FIG. 5 , insert  76  is shown separate from steel sleeve  74 . Mounted on bearing sleeve  72 , one above the other, are two shock absorbing mechanisms  84  ( FIG. 5 ). 
     The housing  110  of each shock absorbing mechanism  84  is fixed to steel sleeve  74 , and its piston  112  is connected to net  20 . The connection shown in  FIGS. 3 and 8  are but exemplary of the many ways of attaching net  20  to piston  112 . 
     In one embodiment, shock absorber  84  is hydraulic with about a 50,000 pound resistance with a twelve inch stroke and an accumulator with a 5,000 pound return force. In a another embodiment, shock absorber  84  is hydraulic with about a 20,000 pound resistance with a four foot stroke and an accumulator with a 5,000 pound return force. 
     As best seen in  FIG. 5 , steel sleeve  74  has flanges  116  which connect to shock absorber flange  114 . Shock absorber cylinder  110  is removably mounted thereto by flanges  114 . Shock absorber piston  112  is removably attached to the net  20 . In one embodiment, the attachment is effected by means of a threaded extension  118  of piston  112  which is received in an internally threaded sleeve-bolt (not shown) attached to the net  20 . Preferably, the attachment is effected by means of an eyelet extension  119  of piston  112 , as shown in  FIGS. 6-7 , through which a cable, clamp or other appropriate securing mechanism may be passed in order to secure the net  20  to the piston  112 . 
       FIGS. 6A and 6B  illustrate a preferred embodiment of the shock absorbing mechanism. Shock absorbers  84  are shown in their quiescent state and their expanded state, respectively. Being top views, only the top shock absorber  84  is seen, the other lying directly beneath the one visible. In the quiescent State ( FIG. 6A ), net  20  is stretched transversely across roadway  10  in the manner exemplified by bottom net  20  in  FIG. 1 . As shown in  FIG. 6A , net  20  has not yet been subject to collision with a vehicle. 
     Shock absorber  84  is normally in a compressed state, secured by a threshold force securing mechanism. The mechanism is capable of withstanding a threshold tensile force. In one embodiment, a threshold force securing mechanism includes a series of shear pins  100  inserted through a shear pin collar  101  into a shear pin ring  102 . The shear pin collar  101  may be integral or separate from other parts of the shock absorber. The shear pin optionally may be secured by a set screw  103 . One can readily envision other threshold force securing mechanisms that may be used in combination with, or instead of, a shear pin. For example a securing mechanism such as a brake pad, or a counterweight, or other counter-force may be used. The threshold force securing mechanism allows the shock absorber  84 , without expanding from its compressed state, to pull net  20  taut. The shock absorber on the other side of roadway  10 , in an identical configuration, will pull the other side of the net  20  taut. Typically, capture net  20  is installed with a 5,000-10,000 pound pre-tension horizontal load on its cables. 
     When an automobile  26  collides with net  20 , the automobile deflects the net, causing it to exert a tensile force exceeding the minimum threshold force upon shock absorber  84 . When the threshold force means includes shear pins, the tensile force causes the pins to shear and thereby permits the expansion of piston  112  of shock absorber  84  against the resistance of the hydraulic fluid in cylinder  110  ( FIG. 6B ). Shock is thereby absorbed during its expansion, while the force of the net  20  also rotates shock absorber  84  and bearing sleeve  72 . Forces applied upon net  20  are thereby translated through the center of stanchion  32 , which is solidly anchored in foundation  34 . Energy is distributed among and absorbed by the net  20 , the shock absorbers  84  and the stanchion  32 . This permits a relatively compact size while being effective in resisting applied forces. 
     A second embodiment of the shock absorbing mechanism includes a torque protection structure. In a preferred aspect as illustrated in  FIGS. 7A and 7B , shock absorbers  84  include a protective sleeve  111  which adds structural strength to resist deformation of the housing  110  or other parts of the shock absorber  84  due to the torque that the net  20  exerts upon capturing an automobile and deflecting shock absorbers  84 . The protective sleeve  111  may be made of any suitable structural material, but is preferably aluminum or steel. 
     Referring to  FIGS. 1 ,  3 , and  8 , the restraining mechanism includes a net  20  comprising a plurality of horizontally extending structural cables  136  made of one inch galvanized structural strands with a breaking strength of sixty-one tons or more. In one embodiment of the restraining mechanism, the structural cables  136  are connected by a plurality of vertically extending cables  138 , as shown in  FIG. 1A . These vertical cables  138  are preferably five-eighths inch galvanized structural strands with a mini mum breaking strength of twenty-four tons, connected to horizontal strands  136  through swaged sockets. 
     In another embodiment of the restraining mechanism, the structural cables  136  are connected by horseshoe cable  138 , as shown in  FIGS. 1B ,  3  and  8 . Preferably, the horseshoe cable comprises wire rope and may be secured to the structural cables by wire rope cable clamps  140 . The horseshoe cable may comprise a plurality of cables, but it is preferred that it be more unitary. The horseshoe cable design provides exemplary automobile capturing properties by allowing the net to wrap around the automobile, preventing it from slipping over the net. As seen in  FIGS. 1B ,  3  and  8 , the cable extends substantially horizontally in a wave pattern with vertical amplitude, having peaks, valleys and midpoints. In the embodiment shown in these figures, the peaks are located at the top horizontal cable, the valleys are located at the bottom horizontal cable, and the midpoints are located at the middle horizontal cable. It is evident from the figures that the tangents of the wave midpoints are more than 90 degrees from tangents of the peaks and valleys. 
     Returning to  FIGS. 4A and 4B , a preferred form of the lift mechanism will now be described. Steel sleeve  74  of bearing sleeve  72  has integrally fixed thereto a lift flange  154 , shown as circular in  FIGS. 4 and 5 , but which could be of any suitable configuration. It is convenient and practical to make bearing sleeve  72  complete at the factory. Bronze insert  76  is press-fit into steel sleeve  74  and reamed to size, and flanges  116  and  154  are welded to sleeve  74 . The unit is then ready to be brought to the site and simply installed on steel pipe  48  which was previously milled to mate with insert  76 . 
     Lift flange  154  rests on caps  156  of lifting screws  158  of lifting jacks  160 . Lifting jacks  160  should preferably be capable of supporting a minimum of 5,000 pounds at a screw extension of forty-eight inches and are supplied with motors  162  ( FIG. 2 ) and speed reducers (not shown) which are preferably capable of lifting 3500 pounds per jack forty-eight inches in twenty seconds. The operation of lifting jacks  160  can conveniently be synchronized through the use of rotary limit switches. Lifting jacks  160  are mounted on base plate  164 . Base plate  164  can desirably be welded to steel pipe  48 . Integrally depending from base plate  164 , and thereby controllably spaced appropriately, are a pair of three inch steel pipes  166  which provide pockets  168  for lifting screws  158 . Integrally constructing pipe  48 , base plate  164 , and pipes  166  prior to removal to the site also simplifies on-site construction, for they can be brought to the site as a unit and simply dropped into place. Even more preferably, the unit may be pre-installed (off-site) in bunker  30  which itself may be brought to the site and installed. 
     Housing  22  is shown in  FIG. 1  is preferably a prefabricated enclosure with stainless steel outer panels so that it can withstand even the most rigorous of weather conditions. The side panels of housing  22  may be hinged for easy access, or housing  22  may be a unitary enclosure which is removable from bunker walls  36 . Within housing  22 , a stainless steel roll up door (not shown) may be included, which is raised by net  20  and which closes automatically due to gravity. 
     In operation, a control system (not disclosed) will sense the presence of an oncoming train and will thereby control net operations. Lift motors  162  will be synchronously actuated so that lift screws  158  of lift jacks  160  will raise bearing sleeve  72  and therewith net  20 . Should a vehicle crash into net  20 , net  20  will deflect, rotating shock absorbing mechanisms  78  about axis  52  of stanchion  32  and expanding hydraulic shock absorbers  84  to restrain the vehicle. The restraining forces will act through axis  52 , placing the strain upon a concrete filled steel pipe embedded solidly in a concrete foundation. After the train passes, the control system will reverse motors  162  to lower net  20  into slot  24  of concrete structure or net slot  58 . 
     In addition to railroad crossings, the system can also be used in a variety of other applications, including HOV lane traffic control, drawbridges, security gates, or crash cushion applications. One can readily appreciate that the control system for such applications may differ from that used in a railroad crossings. At security gates, for example, the restraining net or other barrier would normally be in a raised ‘position, and actuation of the security system (e.g., by a guard, a key card, keyboard punch, etc.) would lower the barrier and permit passage. 
     EXAMPLES 
     An embodiment similar to that shown in  FIGS. 3A and 3B  was constructed without ground retractability, as follows. The overall width of the installation was 18.4 m (60.4 ft) centerline to centerline of the stanchions. The net width was 105 m (34.5 ft). The uninstalled constructed net height was 0.9 m (3.0 ft). The height of the net when installed and tensioned was 1.0 m (3.3 ft) to the center of the top cable and 0.2 m (0.7 ft) to the center of the bottom cable as measured at the centerline of the net assembly. A measure of the tension was recorded in the top and bottom cables of 27.5 kN (6182.3 lb) and 17.5 kN (3934.2 lb), respectively. 
     The cable net was constructed of three equally spaced horizontal members. The top and bottom horizontals were 19 mm (0.8 in) diameter Extra High Strength (EHS) wire strand. The center horizontal was 16 mm diameter 6×26wire rope. The horseshoe cable net members were fabricated of a single 16 mm (0.6 in) diameter 6×26 wire rope. The wire rope was woven up and down along the net width and attached to the top and bottom horizontal wire strand members with three 19 mm (0.8 in) cable clamps at each location and a single 32 mm (1.3 in) modified cable clamp where the rope passed over the center strand. The ends of the top and bottom strands were fitted with Preformed Line Products™ 1.8 m (6.0 ft) Big Grip Dead Ends. The net was attached on one side to shock absorbers with a 32 mm (1.3 in)×457 mm (18 in) turnbuckle and 19 mm (0.8 in) clevis at the top and bottom horizontal strand locations. The opposing net end was connected to shock absorbers with a 19 mm (0.8 in) clevis at the top and bottom horizontal strand locations. 
     The stanchions were fabricated from two sections of steel pipe to form a rotating or hinged anchor system. The anchored inner section of the stanchion was fabricated from A36 steel pipe 305 mm (12.0 in) O.D., 25 mm (1.0 in) wall×1372 mm (54.0 in). Additionally, two 6 mm (0.25 in) rolled bronze plates were welded to each inner section to form bearings. A 6 mm (0.3 in) thick×54 mm (2.1 in) wide steel shelf ring was welded to the perimeter of the inner section to vertically support the outer section 152 mm (6.0 in) above the roadway surface. The inner section was fillet welded to a 25 mm (1.0 in)×686 mm (27.0 in)×686 mm (27.0 in) steel plate and anchored with sixteen 25 mm (1.0 in) mechanical anchors. The outer section was fabricated from A36 steel pipe 381 mm (150 in) O.D., 1.9 mm (0.8 in) wall×1372 mm (54.0 in). 
     The hydraulic shock absorber cylinders were 2.9 m (9.6 ft) long overall. The effective piston stroke was 2.4 m (8.0 ft). 
     Although this particular embodiment was not ground retractable, it is understood that a variety of means could be employed to permit partial or complete ground retraction of the net and/or stanchions in this and other embodiments. For example, the vertically slidable bearing sleeve discussed above would be one option for allowing retraction of the net. Another option might be to retract the all or part of the stanchion, for example vertically or by pivoting it about a horizontal axis.