Patent Publication Number: US-2007102689-A1

Title: Cable barrier guardrail system with steel yielding support posts

Description:
TECHNICAL FIELD OF THE INVENTION  
      The present invention relates generally to guardrail systems and more particularly, to a cable barrier guardrail system with steel yielding support posts.  
     BACKGROUND OF THE INVENTION  
      Guardrail systems are widely used along heavily traveled roadways to enhance the safety of the roadway and adjacent roadside. For example, guardrail systems may be used to accomplish multiple tasks, such as containing and redirecting an errant vehicle upon impact. One such system includes a guardrail beam, such as a “W-beam” (named after its characteristic shape), and corresponding support posts. Other systems may utilize cables and corresponding support posts.  
      Support posts may be made of metal, wood, plastic, composites, or other materials. The material(s) forming the support posts may depend upon design and/or economical factors. For example, wood posts may be more readily available and more economical than metal posts in some geographical areas. In other areas, metal (e.g., steel) posts may be more readily available and more economical and may be preferred for their ease of installation and durability.  
      To avoid undesirable effects, it may be desirable that the support posts yield or break away upon impact in the longitudinal direction, thus producing a desired behavior during a collision by a vehicle at the impact site. Steel support posts that are modified to produce desired behavior during a collision have recently become available. Examples include a “hinged breakaway post” described in U.S. Pat. No. 6,886,813, an “energy absorbing breakaway steel guardrail post” described in U.S. Pat. No. 6,254,063, and a “support post” described in U.S. Patent Application No. 2003/0222254. Many such prior attempts require substantial time, money, and resources during fabrication, modification, and/or installation, however. Furthermore, wood posts may not provide sufficient strength to limit lateral deflections to desired levels. Such posts may also deteriorate rapidly from exposure to the elements. As a result, alternate materials are sought.  
     SUMMARY OF THE INVENTION  
      In accordance with a particular embodiment of the present invention, a guardrail system includes at least one cable operable to contain and redirect an errant vehicle. The guardrail system also includes a plurality of guardrail support posts spaced apart in relation to one another. Each support post includes a lower portion, a mid portion, and an upper portion. The lower portion is for installing below grade adjacent the roadway. The mid portion lies substantially adjacent the grade and includes a weakened section operable to weaken the support post about a longitudinal axis. The upper portion is releasably coupled to the at least one cable such that the upper portion is uncoupled from the at least one cable when the support post is displaced.  
      In accordance with another embodiment, a guardrail support post includes a continuous structural member having first and second generally parallel flanges, and a web forming a coupling between and extending generally perpendicular to the first and second flanges. The structural member has a lower portion for installing below grade adjacent the roadway, an upper portion configured to couple with at least one cable, and a mid portion between the upper portion and the lower portion. The upper portion includes a cable slot formed in the web of structural member. The cable slot includes a first portion comprising a plurality of enlarged openings. Each pair of adjacent enlarged openings are separated by a restriction. Each of the plurality of enlarged openings are adapted to receive a cable. A second portion includes a substantially U-shaped configuration and is adapted to receive at least one cable.  
      Technical advantages of particular embodiments of the present invention include a guardrail support post that has sufficient lateral strength to redirect vehicles that collide along the length of the guardrail system at an angle to the flow of traffic with limited deflection and reduced longitudinal strength that mitigates the severity of the interaction (snagging) between an impacting vehicle and the post. Accordingly, a guardrail system of the present invention may provide benefits in terms of space (reduced deflection for a given post spacing) and cost savings (as a result of fewer posts required to achieve a desired deflection).  
      Other technical advantages may include increased flexibility with respect to design requirements of support posts. For example, wood support posts may be utilized in a cable guardrail system, in particular embodiments. Where wood support posts include a modified section, larger posts may be used than in conventional guardrail systems using wood posts. As a result of the increased lateral stiffness of the larger posts, the spacing between support posts may be increased, and less support posts may be required in the overall guardrail system without a resulting increase in deflection. Accordingly, a further technical advantage may include reduced costs associated with the installation and repair of the cable guardrail system. Similarly, if the spacing between support posts is left unchanged, the increased lateral stiffness of the larger posts may result in reduced lateral deflection. Accordingly, the cable guardrail system can be used at more restrictive locations.  
      Additional advantages may be realized by the mechanical coupling of the guardrail support posts to one or more cables used to contain and redirect errant traffic. In particular embodiments, a modified slot may releasably secure the cables with respect to the support post. A first portion of the modified slot may maintain the cables at a desired elevation with respect to the ground. The first portion may also maintain one or more cables in a position that is resistant to release from the support post. A second, generally U-shaped portion may similarly maintain a cable at a desired elevation with respect to the ground. However, the U-shaped portion may increase the strength of the web of the support post and thus provide resistance to the yielding of the support post. Accordingly, the second portion may reduce deflection of the support post.  
      Other technical advantages will be readily apparent to one skilled in the art from the following figures, descriptions and claims. Moreover, while specific advantages have been enumerated above, various embodiments may include all, some or none of the enumerated advantages.  
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
      For a more complete understanding of the present invention, and the advantages thereof, reference is now made to the following brief descriptions, taken in conjunction with the accompanying drawings and detailed description, wherein like reference numerals represent like parts, in which:  
       FIG. 1  illustrates a side view of a guardrail system that incorporates certain aspects of the present invention;  
       FIG. 2  illustrates a perspective view of a guardrail support post upon collision with a vehicle, in accordance with a particular embodiment of the present invention;  
       FIGS. 3A-3C  illustrate a guardrail support post suitable for use with the guardrail system of  FIG. 1 , in accordance with a particular embodiment of the present invention;  
       FIGS. 4A-4C  illustrate a guardrail support post suitable for use with the guardrail system of  FIG. 1 , in accordance with an alternative embodiment of the present invention;  
       FIG. 5  illustrates a perspective view of a guardrail support assembly suitable for use with the guardrail system of  FIG. 1 , in accordance with a particular embodiment of the present invention;  
       FIGS. 6A-6C  illustrate a spacer component for use with the support post of  FIG. 5 , in accordance with a particular embodiment of the present invention; and  
       FIG. 7  illustrates a wood support post suitable for use with the guardrail system of  FIG. 1 , in accordance with an alternative embodiment of the present invention.  
    
    
     DETAILED DESCRIPTION OF THE INVENTION  
       FIG. 1  illustrates portions of a cable guardrail system  10  that incorporates certain aspects of the present invention. Cable guardrail system  10  may be installed adjacent a roadway, to protect vehicles, drivers and passengers from various obstacles and hazards, and may prevent vehicles from encountering roadside hazards and opposing traffic. Guardrail systems that incorporate aspects of the present invention may be used in median strips or shoulders of highways, roadways, or any path that is likely to encounter vehicular traffic.  
      The illustrated portion of cable guardrail system  10  includes a terminal section  12  and a length-of-need (LON) section  14 . Generally, the LON section  14  extends adjacent to a desired length of the roadway. The LON section  14  includes a cable system  16  comprised of at least one cable  18  that operates to redirect errant vehicles. The cable system  16  is supported by support posts  20 . In the illustrated embodiment, cable system  16  includes three cables  18  (upper cable  18   a,  middle cable  18   b,  and lower cable  18   c ). Other embodiments, however may include a cable system  16  that has as few as one cable  18  and as many as five or more cables  18 . It is generally recognized that the number of cables may vary depending upon factors such as the type of vehicles using the associated roadway and the hazard which requires installation of cable guardrail system  10 .  
      In particular embodiments, cables  18  comprise wire rope cables; however, other embodiments may include other types of cables, wire rope, or steel strands. One example cable for use in cable guardrail system  10  includes a 0.75″ diameter 3×7 wire rope. Other cables that may be used in cable guardrail system  10  may include wire rope having a diameter of ¼″ to 2″, or any other size suitable for use in cable-type guardrail systems.  
      Although all cables  18  in cable system  16  may be of a common size, one of ordinary skill in the art may recognize that the size of each cable  18  may vary, in certain embodiments. For example, top cable  18   a  may be of a larger diameter than middle cable  18   b  and lower cable  18   c.  Such an embodiment may provide additional resistance for accommodating taller and heavier vehicles, such as semi trailer trucks. For similar reasons, middle cable  18   b  may be of a larger diameter than lower cable  18   c  to provide greater resistance to larger vehicles, such as sport utility vehicles.  
      Terminal section  12  includes cable anchor posts  22 , which each anchor an initiation point of a cable  18  within cable system  16 . In the illustrated embodiment, each cable  18  is anchored or secured by, or coupled to, a separate cable anchor post  22  proximate a ground surface  24 . For example, cable  18   a  is coupled to cable anchor post  22   a,  cable  18   b  is coupled to cable anchor post  22   b,  and cable  18   c  is coupled to cable anchor post  22   c.  Accordingly, since the illustrated cable system  16  includes three cables  18 , terminal section  12  includes three cable anchor posts; however, other embodiments may include a terminal section with fewer or greater than three cable anchor posts. For example, some embodiments of the present invention may include four cable anchor posts that each anchor one of four cables. Cable guardrail systems in accordance with other embodiments may also include terminal systems with more than one cable coupled to a single cable anchor post. For example, one embodiment may include a terminal section with four cables and two cable anchor posts, in which case each cable anchor post may anchor two cables. In such situations, it may be desirable to separately anchor at least some cables to facilitate construction and repair of the system.  
      It should be understood that cable anchor posts  20  of  FIG. 1 , make up only one terminal of a complete cable guardrail system  10 . Thus, cable guardrail system  10  may include an opposite terminal section that includes a number of cable anchor posts positioned on the opposite end of LON section  14 . Such an opposite terminal section may be constructed in essentially the same manner as terminal section  12  illustrated in  FIG. 1 .  
      As described above, cables  18  are also each secured to support posts  20 , which support such cables  18  in a generally horizontal and parallel relation above ground surface  24 . In the illustrated embodiment, cable anchor posts  22  and support posts  20  are securely anchored in concrete footers  26 . However, other embodiments may utilize other mechanisms or methods to anchor cable anchor posts  22  and support posts  20 . For example, some embodiments may utilize sleeves, foundation tubes, ground struts, or trapezoidal soil plates to secure posts of a cable guardrail system.  
      The orientation and spacing of cable anchor posts  22  and support posts  20  may vary in various embodiments. As illustrated in  FIG. 1 , cable anchor posts  22  may be installed in general alignment with each other and with the running of cables  18  along cable guardrail system  10 . In particular embodiments, the spacing between adjacent cable release anchor posts  22  may be approximately 6 feet. In particular embodiments, the spacing between adjacent support posts  20  may be between 6 and 20 feet and may be dependent upon the type of material used to form support posts  20  or the available space or desired deflection of the guardrail system.  
      Cable guardrail system  10  is intended to keep errant vehicles from encountering roadside hazards and opposing traffic during a crash or other hazardous situation. In many instances, cable guardrail system  10  is installed between a roadway and a significant hazard to vehicles (e.g., another roadway, a bridge, cliff, etc.). Therefore, cable guardrail system  10  should be designed to withstand a significant impact from a vehicle leaving the roadway and striking the guardrail at an angle, without substantial failure.  
      However, testing and experience has continuously shown that guardrail systems may actually introduce additional hazards to the roadway and surrounding areas. This is particularly true with respect to vehicles that impact the cable guardrail system  10  adjacent its terminal section  12 , in a direction generally parallel to the roadway. For example, if the cable guardrail system  10  were rigidly fixed in place during a crash, serious injury and damage may result to the errant vehicle, its driver and passengers.  
      In particular embodiments, cable anchor posts  22  may include releasable cable anchor posts such as those described in U.S. Pat. No. 6,932,327 (“&#39;327 patent”). As a result, each releasable cable anchor post may yield or break-away and release its respective cable in the event of an impact by a vehicle striking the post. The performance of cable guardrail system  10  may be improved since the vehicle is less likely to become hung up on the cable anchored post. Conversely, in the event that a vehicle strikes cable guardrail system  10  at a location other than a particular releasable cable anchor post, then releasable cable anchor posts resist release of their respective cables and hold and anchor their respective cables. Thus, if a vehicle impacts cable guardrail system  10  at an angle to the flow of traffic at any point along its length-of-need (“LON”), then each releasable cable anchor post may be designed to hold their respective cables to aid in the redirection of the vehicle toward the roadway. In particular embodiments, each releasable cable anchor post may hold and anchor the cable(s) that it secures in the event of an impact to a separate releasable cable anchor post. Furthermore, having particular cables of the system separately anchored and released may facilitate construction and repair of the system and reduce cost.  
      Improperly designed posts in the LON section of a guardrail system may also introduce additional hazards to the roadway and surrounding areas. This is particularly true with respect to vehicles that impact the guardrail system at an angle along the LON section. The vehicle may encounter (contact) numerous support posts which if not properly designed may induce and increase risk to the driver and passengers. Additionally, the guardrail may fail in its purposes of containing and redirecting the errant vehicle.  
      In accordance with the teaching of the present invention, support posts  20  in LON section  14  have been modified to decrease the strength of support posts  20  in a direction generally parallel to axis  28  (generally along the direction of traffic) without substantially decreasing its strength in a direction generally perpendicular to axis  28  (out of the page in  FIG. 1 ). Stated differently, support posts  20  exhibit adequate strength in the lateral direction to contain and redirect an impacting vehicle within a desired deflection distance but sufficiently low strength in the longitudinal direction to mitigate the contact or snagging forces between the impact in vehicle and support posts. Accordingly, if a vehicle impacts cable guardrail system  10  “head-on” adjacent support posts  20 , support posts  20  will tend to yield, break-away, fracture, buckle, or otherwise be displaced while allowing the vehicle to decelerate as it impacts consecutive support posts.  
       FIG. 2  illustrates a guardrail support post  20  after collision with a vehicle, in accordance with a particular embodiment of the present invention. Specifically, support post  20  has operated in the preferred manner and has activated as designed upon collision by an errant vehicle. Specifically, and as will be described in more detail below, support post  20  includes a weakened or modified section that lies substantially near or adjacent to the surface  24  of the ground. The weakened or modified section decreases the structural integrity of support post  20  in a direction generally parallel to the direction of traffic. Accordingly, support post  20  is displaced with respect to its original position. As illustrated in  FIG. 2 , buckled support post  20  lies on the surface  24  of the ground, bent at an approximately ninety degree angle about the weakened or modified section after impact. The buckled support post  20  mitigates the severity of the interaction (snagging) between the impacting vehicle and support post  20 .  
      Although support post  20  has buckled, cables  18  remain in substantially the same position with respect to the road as the position of cables  18  prior to the collision. The position of cables  18  is maintained due to the uncoupling of support post  20  with cable system  16  upon impact. Specifically, and as will be described in more detail below, support post  20  is configured to releasably couple to cable system  16 . Upon impact, the coupling mechanism releases cables  18  such that cable system  16  remains intact and in position to operate to redirect the errant vehicle to prevent the vehicle from encountering roadside hazards and opposing traffic. Thus, the impact performance of cable system  16  of guardrail system  10  is not compromised by the modified support post  20 .  
       FIGS. 3A-3C  illustrate a guardrail support post  40 , in accordance with a particular embodiment of the present invention. Support post  40  includes an elongated, continuous structural member of a standard Wide flange configuration. In particular, support post  40  includes two flanges  42  and  44 , that are generally parallel with one another, and in a spaced relation. A web  46  forms the coupling between flanges  42  and  44 .  
      With regard to a Wide flange shape used as a guardrail post, the cross section is typically shaped like the letter “I” as shown in  FIG. 3C . The cross section has two major axes for bending. The “weak” axis, denoted as “W” in  FIG. 3C , generally refers to a central axis that extends through the web and is perpendicular to the flanges. The “strong” axis, denoted as “S” in  FIG. 3C , generally refers to a central axis that is perpendicular to the web and parallel to the planes of the flanges. The weak axis for a conventional installation of guardrail extends generally transversely to the road. The strong axis extends generally along the roadway.  
      In a particular embodiment, the Wide flange comprising support post  40  is a standard S4×7.7, which has a nominal four-inch depth and weighs 7.7 pounds per foot. Those of ordinary skill in the art will recognize, however, that wide flange beams may be available in many different sizes, and many different sizes may be appropriate for use as a support post  40 . Accordingly, in alternative embodiments, support post  40  may include a standard W6×9, which may have a six-inch depth and weigh from eight and one half pounds per foot to nine pounds per foot. The standard W6×9 is commonly used in fabricating support posts for guardrail installations. In fact, one advantage of the present invention is the ability to re-use existing, standard equipment to fabricate, modify, and install support post  40 , without substantial modification to the equipment. In still other embodiments, support post  40  may include a standard W8×10, which may have an eight-inch depth and weigh approximately ten pounds per foot. As a further modification, it is recognized that persons skilled in the art may utilize other structural shapes for the support posts. Such shapes may include but are not limited to “I-beam,” “H-beam,” “W-beam,” “S-beam,” “M-beam,” or the term “shape” may be substituted for “beam.” Additionally, a non-wide flange such as a “C-channel” may be substituted for the wide flange support post.  
      Support post  40  is relatively “weak” about axis W, and relatively “strong” about axis S. For the reasons described above, support post  40  is normally installed along a roadway such that weak axis W is generally perpendicular to the direction of traffic, and strong axis S is generally parallel to the direction of traffic. Accordingly, support post  40  is typically able to withstand a significant impact (e.g., with a car traveling at a high rate of speed) about the strong axis S without substantial failure. However, support post  40  is intentionally designed such that failure will more readily occur in response to an impact about the weak axis W such that damage and deceleration of the impacting vehicle are minimized.  
      In particular embodiments, support post  40  may have a length on the order of approximately 3′-11¼″ and includes an upper portion  48 , a lower portion  50 , and a mid portion  52  which spans between upper portion  48  and lower portion  50 . Upper portion  48  includes a cable slot  54  that is adapted to releasably couple to a cable system (e.g., cable system  16  that includes cables  18 ) upon support post  40 . Lower portion  50  is suitable for installation below grade, as part of a guardrail support system. Mid portion  52  includes two cutouts  56 , which are configured to weaken support post  40  about the weak axis W, to more readily allow for buckling due to impact from a vehicle along that direction. The overall length of support post  40 , and its upper, lower and mid portions may vary significantly, within the teachings of the present invention.  
      Cutouts  56  are positioned within mid portion  52  to weaken support post  40  about weak axis W, substantially adjacent to or near grade (when installed). When cutouts  56  are positioned at or near grade, the configuration of support post  40  may accommodate yielding of support post  40  approximately at or near grade, allowing support post  40  to “fold” over from the point of yield, upward or otherwise be displaced. It will be recognized by those of ordinary skill in the art that the size, configuration, location and number of cutouts may be varied significantly within the teachings of the present invention.  
      In a particular embodiment, cutouts  56  may be positioned approximately 2′-7¾″ below a top edge  58  of support post  40 . However, the location of cutouts  56  may vary in accordance with the teachings of the present invention. As described above, the configuration of  FIGS. 3A-3C  envisions that cutouts  56  may occur approximately at or near grade level. In other embodiments, cutouts  56  may occur below grade or above grade. The depth of cutouts  56  below grade, however, should not exceed an amount that will prevent support post  40  from yielding at or near the location of cutouts  56 . At some depth below grade, the surrounding earthen (or other) material may reinforce lower portion  50  of support post  40  to an extent that will no longer permit such yielding to occur.  
      The height of cutouts  56  above grade should not exceed a point at which support post  40  will yield or break-away at cutouts  56 , and leave a “stub” above grade which can snag vehicles, and otherwise cause excessive injury and/or excessive damage. Such a stub could be detrimental to the redirective effect of the guardrail system in which support post  40  is operating.  
      Support post  40  includes a modified cable slot  54  having a configuration that allows for the releasable coupling of support post  40  with one or more cables. In the illustrated embodiment, cable slot  54  is formed in web  46  of the wide flange support post. Forming cable slot  54  in web  46  eliminates requirements for bolts, hooks, or other mechanical attachments to releasably secure cable system  16  to support post  40 . Furthermore, in the illustrated embodiment, modified cable slot  54  comprises an open slot since it is open at top edge  58  of support post  40 . Because cable slot  54  is open, cables  18  may be slid into cable slot  54  during assembly of cable guardrail system  10 . Thus, cable slot  54  aids in the efficient installation of cable guardrail system  10 .  
      Modified cable slot  54  is an elongated slot extending from top edge  58  towards bottom edge  60  of support post  40 . The length of modified cable slot  54  may be selected in part based on desired vertical spacing of cable system  16  relative to the adjacent roadway. The length of modified cable slot  54  may also be selected to accommodate the number of cables  18  which will be installed therein and desired vertical spacing between each cable  18 .  
      In the illustrated embodiment, modified cable slot  54  is of a modified U-shaped configuration that is defined in part by first edge  61 , second edge  62  and bottom edge  63 . A first portion  64  of each of first edge  61  and second edge  62  is of a wave-like configuration. Thus, one or more restrictions  65  are formed within cable slot  54 .  
      Restrictions  65  of cable slot  54  may be defined in part by corresponding projections  66  on first and second edges  61  and  62 . First and second edges  61  and  62  of cable slot  54  preferably include alternating tapered or sloping surfaces which form projections  66 . The same tapered or sloping surfaces also form enlarged openings  67  within cable slot  54 . The location of enlarged openings  67  are preferably selected to correspond with approximate desired locations for cables  18 . Thus, in the illustrated embodiment, each of first and second edges  61  and  62  include three projections  66 , defining two openings  67  there between. As will be described in more detail below, such a configuration allows the assembly of three or fewer cables  18  within cable slot  54 .  
      In various embodiments, the gap or spacing formed between corresponding projections  66  on first and second edges  61  and  62 , respectively, is generally selected to be greater than the outside diameter of cables  18 . Specific dimensions between the respective projections are selected to facilitate disengagement between cables  18  as support post  40  with cable slot  54  is bent from a generally vertical position towards a horizontal position while allowing easy installation of cables  18  in cable slot  54 .  
      A second portion  68  of each of first edge  61  and second edge  62  is of a U-shaped configuration. Thus, first and second edges  61  and  62  of second portion  68  have a generally smooth profile and extend generally parallel with each other in a direction that is generally parallel to the longitudinal axis of support post  40 . In particular embodiments the width of the space formed between first and second edges  61  and  62  is the same as the width of the space formed between restrictions  65  of first portion  64 . Generally, the width of the space is selected to be slightly greater than the outside diameter of cables  18 . The bottom edge of second portion  68  of cable slot  54  corresponds generally with bottom edge  63  and includes but is not limited to a substantially round radius of curvature. The radius of curvature may be such as to support a cable  18  within cable system  16  in second portion  68  of modified cable slot  54 .  
      In the illustrated embodiment, modified cable slot  54  includes three restrictions  65  formed within cable slot  54 . In particular embodiments, the first (or upper) restriction  65  may be formed approximately ⅝″ from the top edge  58  of support post  40 . The second (or middle) restriction  65  may be formed approximately 4 5/16″ below the first restriction. The third (or lower) restriction  65  may be formed approximately 4 5/16″ below the second restriction.  
      Restrictions  65  are formed by projections  66  in first and second edges  61  and  62 , respectively. In particular embodiments, the width of the space defined by restrictions  65  may be approximately 13/16″. Similarly, the width of the U-shaped slot defined by first and second edges  61  and  62  of second portion  68  may also be on the order of approximately 13/16″. Conversely, the width of the space defined by openings  67  may be approximately 1⅜″. Thus, modified cable slot  54 , as illustrated, is configured to secure any size cable  18  that may be slightly smaller than 13/16″.  
      As stated above, the location of cables  18  is related to the location of openings  67  within cable slot  54 . Specifically, a first (or upper) opening  67  may be located approximately 2 25/32″ from top edge  58  of support post  40 . Thus, upper cable  18   a  may be supported at an elevation that is approximately 2 25/32″ from the top edge  58  of support post  40 . Second (or lower) opening  67  may be approximately 4 5/16″ below the first opening  67 . As a result, middle cable  18   b  may be supported at an elevation that is approximately 7 3/32″ below top edge  58  of support post  40 . Finally, lower cable  18   c,  which may rest on lower edge  63  of cable slot  54 , may be supported at an elevation that is approximately 11 13/16″ from the top edge  58  of support post  40 . The radius of curvature corresponding to bottom edge  63  of cable slot  54  is approximately 13/32″ in the illustrated embodiment.  
      Support post  40  is a single, continuous structural member that does not require any labor in field assembly, welding, or special handling, in particular embodiments. With the exception of modified cable slot  54  and cutouts  56  support post  40  has a continuous, generally uniform cross-section from top edge  58 , to a bottom edge  60 . Therefore, fabrication of support post  40  is simplified, with respect to other multiple component products. Furthermore, support post  40  can be shipped as one piece, and installed as one piece. Many prior attempts that included multiple components that were hinged, or otherwise connected could not be shipped, and/or installed as a single unit without damaging the support post.  
      Similarly, many such prior efforts required specialized equipment for proper installation, and often required a significant amount of field labor to perform such installation. In contrast, support post  40  of the present invention can be installed using traditional guardrail post installation equipment (e.g., guardrail post drivers).  
      As described above, cutouts  56  of support post  40  are configured to reduce the strength of support post  40  about weak axis W, without substantially weakening support post  40  about strong axis S. In the illustrated embodiment, cutouts  56  comprise generally circular openings that have been punched or drilled through support post  40 . In the illustrated embodiment of  FIGS. 3A-3C , cutouts  56  are approximately eleven-sixteenths of an inch in diameter. The edge of each cutout  56  is approximately one quarter of an inch from the edge of the respective flanges.  
      Previous attempts to accommodate yielding of a guardrail support post have often weakened the support post about the strong axis S, which impacts the support post&#39;s ability to redirect a vehicle that collides with the support at an angle relative to the roadway. For this reason, such support posts may be unacceptable for use along a roadway, and may fail to comply with governing federal standards bodies&#39; requirements.  
      Patent Application PCT/US98/09029 (&#39;029 Application) illustrates a support post having slotted openings disposed therein. These slots are substantially longer (vertically) than they are wide (horizontal). The support post of the &#39;029 Application may yield at any point along the slots, and yielding may be based upon imperfections in the material adjacent the slots. By contrast, cutouts  56  provide an enhanced ability to control the point of yield of support post  40  during a collision with a vehicle. By limiting the vertical dimension of cutouts  56 , it is easier to dictate the precise point of yielding of support post  40  along its vertical length.  
      Furthermore, the slots of the &#39;029 Application require the removal of a substantial amount of material from the flange. This weakens the flange along directions other than perpendicular to the web. Furthermore, during a dynamic crash situation, in which the impact may come from any angle, twisting or bending of the flange may result in the flange changing its orientation in response to the initial impact. Accordingly, the support post having vertical slots similar to the &#39;029 Application may fail prematurely along the strong axis and lose its ability to redirect the vehicle and/or result in increased deflections of cable guardrail system  10 .  
      In accordance with the teachings of the present invention, the vertical dimension of each cutout  56  is limited based upon the horizontal dimension of cutout  56 . For example, a ratio of the vertical dimension of any particular cutout may be equal to, or less than three times the horizontal dimension. Alternatively, the ratio may be limited to two times the horizontal dimension. In the illustrated embodiment of  FIGS. 3A-3C , the ratio is 1:1, since cutout  56  is generally a circular opening in support post  40 . The smaller the vertical dimension of the cutout, the more precisely the designer may dictate the point of yield along the vertical length of support post  40 .  
      Modifications, additions, or omissions may be made to support post  40  without departing from the scope of the invention. For example, it will be recognized by those of ordinary skill in the art that the size, configuration, location and number of cutouts, cable slots, and their relationship with each other may be varied significantly within the teachings of the present invention. Additionally, various configurations of cutouts  56  and cable slot  54  are available to a designer of support post  40 , in accordance with the teachings of the present invention. For example, rather than circular openings, cutouts  56  may comprise square, rectangular, triangular, oval, diamond shaped, or practically any other geometric configuration, and still obtain some or all of the benefits described herein.  
      As a further modification, the horizontal orientation of cutouts  56  within flanges  42  and  44  may also be altered significantly, within the teachings of the present invention. In the illustrated embodiment of  FIGS. 3A-3C , the edges of cutouts  56  are located approximately a quarter of an inch from outer edges of flanges  42  and  44 . However, in alternative embodiments, cutouts  56  may be located closer to such edges, or further from such edges. In one embodiment, cutouts  56  may be configured such that they extend all the way to the edge of the flange, such that there is a break in material beginning at the edge. In this manner, a traditional punch could be employed at the edge, to form a semi-circular opening that extends to the edge of the flange.  
      Alternatively, a saw cut could be employed from the outer edge of the flange, and extending inward, to form cutouts  56 . In this manner, the saw cut would form the starting point of the likely point of yield along the weak axis of the support post. Rather than a saw cut, a similar configuration may include a slot in which the longest dimension extends horizontally through the flange. Such a slot may begin or terminate at the edge of the flange, or otherwise be disposed completely within the material of the flange.  
      As still another modification, various configurations of cable slot  54  are available to a designer of support post  40 , in accordance with the teachings of the present invention. Thus, the modified cable slots illustrated in  FIGS. 3A-3C  are just one example of a mechanism that may be used to couple cable system  16  to support post  40 . Other such mechanisms may include U-shaped slots, trapezoidal slots, triangular slots, circular holes, or any other shape aperture for mechanically coupling cable system  16  to support post  40 . The dimensions and configurations of such coupling mechanisms may vary depending upon the size of the cables being used and the desired heights of the cables with respect to the roadway. Additionally, support post  40  may include multiple apertures and each aperture may be associated with a corresponding cable  18  of cable system  16 .  
      In still other embodiments, cable slot  54  may be omitted. Cables  18  of cable system  16  may be fastened to flanges  42  and  44  or to another component of support post  40  using J bolts, I bolts, U bolts, locking hook bolts, bent pieces of plate, or another fastener or mechanical connection. Where cables  18  of cable system  16  are attached to an I-beam support post such as the one illustrated in  FIGS. 3A-3C  using a fastener or other mechanical connection, it is recognized that cables  18  may be coupled to a single side of support post  40 . In other embodiments, cables  18  may be alternated such that, for example, the upper and lower cables  18   a  and  18   c  may be attached to a first flange  42  of support post  40  and middle cable  18   b  may be attached to a second flange  44  of support post  40 .  
       FIGS. 4A-4C  illustrate a guardrail support post  70 , in accordance with another embodiment of the present invention. Like support post  40 , support post  70  includes an elongated, continuous structural member of a standard Wide flange configuration. Specifically, support post  70  includes two flanges  72  and  74 , that are generally parallel with one another, and in a spaced relation. A web  76  forms the coupling between flanges  72  and  74 . In a particular embodiment, support post  70  may comprise an S4×7.7 Wide flange. Thus, support post  70  may be very similar in configuration to support post  40 , although certain of the dimensions of relative aspects and components may be slightly different.  
      In the illustrated embodiment, support post  70  is slightly longer than support post  40  of  FIGS. 3A-3C . For example, support post  70  may have a length on the order of approximately 4′-7⅞″ (in a particular embodiment) and may include an upper portion  78 , a lower portion  80 , and a mid portion  82  which spans between upper portion  78  and lower portion  80 . Lower portion  80  and mid portion  82  may be configured substantially like lower portion  50  and mid portion  52  of support post  40  illustrated and described with regard to  FIGS. 3A-3C . Thus, lower portion  80  may be configured to be mounted below the earth&#39;s surface as a support system for cable guardrail system  10 . Mid portion  82  may include a weakening section, such as cutouts  86 , that may reduce the strength of support post  70  about weak axis W, without substantially weakening support post  70  about strong axis S. In the illustrated embodiment, cutouts  86  comprise generally circular openings that have been punched or drilled through support post  70 .  
      Upper portion  78  includes a modified cable slot  84  that is adapted to releasably couple to a cable system (e.g., cable system  16  that includes cables  18 ) upon support post  70 . Like modified cable slot  54  of FIGURES  3 A- 3 C, modified cable slot  84  has a configuration that allows for the releasable coupling of support post  70  with one or more cables. In the illustrated embodiment, modified cable slot  84  is formed in web  76  of the wide flange support post. Like modified cable slot  54 , modified cable slot  84  comprises an open, elongated slot extending from top edge  86  towards bottom edge  88  of support post  70 .  
      In the illustrated embodiment, the length of modified cable slot  84  is slightly longer than modified cable slot  54  of  FIGS. 3A-3C . As described above, the length of modified cable slot  84  may be selected based at least in part on the desired vertical spacing of cable system  16  relative to the adjacent roadway and/or the number of and spacing between each cable  18  in cable system  16 . The length of modified cable slot  84  may also be selected based upon the number of cables  18  included in cable system  16 .  
      In the illustrated embodiment, modified cable slot  84  is defined in part by first edge  91 , second edge  92  and bottom edge  93 . A first portion  94  of each of first edge  91  and second edge  92  is of a wave-like configuration and includes five restrictions  95 . Restrictions  95  are defined in part by corresponding projections  96  on first and second edges  91  and  92 . Restrictions  95  are separated by enlarged openings  97  within cable slot  84 .  
      As described above, cables  18  within a cable system  16  are preferably disposed at different heights relative to the ground and relative to each other. Varying the vertical spacing between cables  18  often provides a much wider lateral catch area for vehicles impacting with cable guardrail system  10 . The vertical spacing between cables  18  may be selected to satisfactorily contain both pickups and, to some extent, even larger trucks with a relatively high center of gravity, as well as vehicles with a low front profile and low center of gravity. Thus, in particular embodiments, the location of at least a portion of enlarged openings  97  are preferably selected to correspond with approximate desired locations for cables  18 . In the illustrated embodiment, each of first and second edges  91  and  92  include five projections  96 , defining four openings  97  there between. Where a cable  18  is supported in each opening  97 , such a configuration allows the assembly of as many as five cables  18  within cable slot  84  (one cable per opening  97  and one cable per elongated U-shaped slot within second portion  98  of cable slot  84 ).  
      It is recognized, however, that the ratio of openings  97  to cables within cable system  16  is not necessarily 1:1. Accordingly, modified cable slot  84  may include more openings  97  than there are cables  18  within cable system  16 . In such embodiments, spacers (described in greater detail below with respect to  FIGS. 5 and 6 A- 6 C) may be used within some of openings  97 . As a result, though configured for supporting as many as five cables, modified cable slot  84  may receive fewer than five cables  18 , in particular embodiments.  
       FIG. 5  illustrates a guardrail support assembly  100 , in accordance with a particular embodiment of the present invention. Specifically, guardrail support assembly  100  includes a support post  102 , one or more spacers  104 , and a retaining band  106 . As illustrated guardrail support assembly is used to support an upper cable  18   a,  a middle cable  18   b,  and a lower cable  18   c.  The components of guardrail support assembly  100  may be best understood in the context of a typical installation, which may begin with the installation of support post  102 . In particular embodiments, support post  102  may be configured similar to support post  40  or support post  70  described above with respect to  FIGS. 3A-3C  and  4 A- 4 C, respectively. Accordingly, support post  102  may include an I-beam having an upper portion configured to mechanically couple to cables  18 .  
      Support posts such as support post  102  may be installed at desired locations adjacent to a roadway and/or median. Various techniques may be used to anchor support post  102  with respect to the ground. For example, support post  102  may be securely anchored in a concrete footer, such as concrete footer  30  illustrated in  FIG. 1 . In other embodiments, sleeves, foundation tubes, ground struts, or trapezoidal soil plates may be used to secure support post  102  under a ground surface. Releasable cable anchor posts such as those described with regard to  FIG. 1  may also be similarly installed.  
      After the installation of support post(s)  102  and terminal posts, cables  18   a,    18   b,  and  18   c  (or any number of desired cables) may be rolled out and placed on the ground extending generally longitudinally the desired length of the cable guardrail system. One end of each cable  18  may be connected with a respective cable anchor post (not shown).  
      Lower cable  18   c  may be inserted into modified cable slot  108  and may be slid down modified cable slot  108  until lower cable  18   c  rests on the bottom edge  110  of cable slot  108 . A spacer  104   a  may then be inserted or dropped into cable slot  108  to rest on lower cable  18   c.    FIGS. 6A-6C  illustrate an exemplary spacer  104  for use with the support post  102  of  FIG. 5 . In particular embodiments, spacer  104   a  may include a modified H-shaped member having two flanges  112  and  114 , that are generally parallel with one another, and in a spaced relation. A web  116  forms the coupling between flanges  112  and  114 .  
      Spacer  104   a  may be formed from a wide variety of materials including polymeric materials, elastomeric materials, recycled materials, structural foam materials, composite materials, wood, and/or lightweight metal alloys. In particular embodiments, spacer  104   a  may be injection molded from rubber and/or other plastic materials. The present invention is not limited, however to forming spacer  104   a  from any specific type of material or with any specific dimensions or configurations.  
      Web  116  of spacer  104   a  has a width that is narrower than the narrowest portion of modified cable slot  108  of support post  102 . Accordingly, where support post  102  includes an S4×7.7, the width of web  116  may be on the order of or less than approximately ¾″. As a result, spacer  104   a  and, specifically, web  116  of spacer  104   a  may be slid through the opening of modified cable slot  108  such that flanges  112  and  114  of spacer  104   a  are disposed on opposite sides of the web member of support post  100 .  
      Additionally, each of flanges  112  and  114  have a width that is greater than the widest portion of modified cable slot  108 . As a result, flanges  112  and  114  operate to secure spacer  104   a  in modified cable slot  108 . In the illustrated example, where support post  102  comprises an S4×7.7, flanges  112  and  114  may have a width on the order of approximately 2″. However, other configurations may be suitable for spacer  104   a.  It is only material, however that flanges  112  and  114  are wider than the widest portion of modified cable slot  108  and narrower than the length of the web portion of the support post  102 .  
      As illustrated, web  116  of spacer  104   a  is tapered at both a first (upper) end  118  and a second (lower) end  120 . Accordingly, web  116  of spacer  104   a  includes a first tapered portion  122  and a second tapered portion  124 , which are separated by a substantially vertical portion  126 . Thus, while the substantially vertical portion  126  of web  116  may have a width on the order of approximately ¾″, the tapered portion  122  of web  116  at upper edge  118  may have a width on the order of approximately ½″. Similarly, tapered portion  124  of web  116  at lower edge  120  may have a width on the order of approximately ½″. When configured as described or similarly configured, tapered portions  122  and  124  may improve the ease with which spacer  104   a  may be slid onto support post  102 .  
      Returning to  FIG. 5 , after the installation of spacer  104   a,  middle cable  18   b  may be inserted into modified cable slot  108  of support post  102 . Middle cable  18   b  may be slid down modified cable slot  108  until middle cable  18   b  rests on the upper edge  118  of spacer  104   a.  Thus, lower cable  18   c  and middle cable  18   b  are separated by spacer  104   a  when assembled with support post  102 . Accordingly, the height of spacer  104   a  (3 9/16″ in a particular embodiment) is preferably selected to correspond with the desired vertical spacing between lower cable  18   c  and middle cable  18   b.    
      After the insertion of middle cable  18   b,  a spacer  104   b  may then be inserted or dropped into modified cable slot  108  to rest on middle cable  18   b.  In particular embodiments, spacer  104   b  may be configured substantially similar to spacer  104   a  described above. Upper cable  18   a  may then be inserted into modified cable slot  108  of support post  102 . Upper cable  18   a  may be slid down modified cable slot  108  until upper cable  18   a  rests on the upper edge  118  of spacer  104   b.  Thus, middle cable  18   b  and upper cable  18   a  are separated by spacer  104   b.  Accordingly, the height of spacer  104   b  (3 9/16″ in a particular embodiment) is preferably selected to correspond with the desired vertical spacing between middle cable  18   b  and upper cable  18   a.    
      One or more retaining bands  106  may then be secured around the exterior of support post  102  between upper cable  18   a  and middle cable  18   b  and/or between middle cable  18   b  and lower cable  18   c.  In particular embodiments, retaining band(s)  106  may be placed on the exterior of support post  102  to provide additional strength to support post  102 . For example, retaining band(s)  106  may increase the strength of support post  102  and compensate for the weakened web that results from material being removed for modified cable slot  108 . Retaining band(s)  106  may also operate to keep the cable-support post connection intact longer when impacted by an errant vehicle.  
      Retaining band(s)  106  may be formed from various types of metals, elastomeric materials and/or composite materials. For some applications, retaining band(s)  106  may be formed from a relatively strong steel alloy to provide additional support to allow post  30  to handle forces imposed on support post  102  by cables during a vehicle impact with cable guardrail system  10 .  
      In a particular embodiment, retaining band(s)  106  may comprise a metal strap having a total length of approximately 14 13/16″ before being wrapped around support post  102 . The width of the metal strap may be on the order of approximately 1¼″ and the depth (or thickness) may be on the order of approximately 0.04″. After installation around support post  102 , the opposites ends of a metal strap having a total length of approximately 14 13/16″ may overlap by approximately 11/16.  
      After the assembly of retaining band(s)  106  around support post  102 , a first end of each cable  18  may be secured to a cable anchor post of a first terminal section, such as cable anchor post  22  of terminal section  12  illustrated in  FIG. 1 . Appropriate tension may then be applied to each cable  18 , and the second end of each cable  18  may be secured to a cable anchor post of a second terminal section.  
      When installed adjacent a roadway, support post  102 , as part of an overall cable guardrail system, protects vehicles, drivers, and passengers from various obstacles and hazards. Specifically, and as described above, support post  102  is intentionally designed to preferably buckle about a weakened section when struck by an errant vehicle. However, cables  18  may remain in substantially the same position with respect to the road as the position of cables  18  prior to the collision. The position of cables  18  is maintained due to the uncoupling of support post  102  with the cables  18  upon impact. Specifically, as support post  102  buckles, cables  18  slip out of modified cable slot  108  through the open area at top edge  54 . In the process, retaining band(s)  106  and spacers  104  may be disengaged from support post  102 . Because cables  18  may remain in substantially the same position as their original position with respect to the roadway, cables  18  may operate to redirect the errant vehicle to prevent the vehicle from encountering roadside hazards and opposing traffic. Repair of the support system may involve the isolated replacement of support post  102  and any damaged components such as spacers  104  and retaining band  106 .  
       FIG. 7  illustrates a wood guardrail support post  150  suitable for use with the guardrail system  10  of  FIG. 1 , in accordance with an alternative embodiment of the present invention. In the illustrated embodiment, support post  150  includes an elongated, continuous structural member comprised of wood. Like support posts described above, support post  150  includes a relatively “weak” axis W, and a relatively “strong” axis S. For the reasons described above, support post  150  is normally installed along a roadway such that weak axis W is generally perpendicular to the direction of traffic, and strong axis S is generally parallel to the direction of traffic. Accordingly, support post  150  is typically able to withstand a significant lateral load applied by cables  18  of cable system  16  without substantial failure. However, support post  50  is intentionally designed such that yielding will more readily occur in response to an impact about the weak axis W.  
      Support post  150  is approximately 6′ long, and includes an upper portion  152 , a lower portion  154 , and a mid portion  156 . In the illustrated embodiment, upper portion  152  includes three pairs of bolt holes  152  that are adapted to receive connectors for the installation of cables  18  of cable system  16 . For example, bolt holes  152  may be adapted to receive U-shaped bolts, hook bolts, or other fasteners. Lower portion  154  is suitable for installation below grade, as part of a guardrail support system. Mid portion  156  comprises a weakened section  160  which is configured to weaken support post  150  about the weak axis W, to more readily allow for yielding due to impact from a vehicle along that direction. The overall length of support post  150 , and its upper, lower, and mid portions may vary significantly, within the teachings of the present invention.  
      Bolt holes  158  include a standard configuration that allow for the installation of cables  18 , upon support post  150 . In general, each pair of bolt holes  158  maintain a cable  18  at a desired distance above grade. However, the number, size, location, and configuration of bolt holes  158  may be significantly modified, within the teachings of the present invention. As just one possible modification, in particular embodiments, each pair of bolt holes  158  may be replaced with a single bolt hole  158 . Such a configuration may be compatible with fasteners such as J bolts in which only one leg of the bolt may penetrate support post  150 . Additionally, it is recognized that while all cables  18  may be support on one side of support post  150  in certain embodiments, other embodiments may include alternating the installation of cables  18  on opposing sides of support post  150 .  
      Weakened section  160  is positioned within mid portion  156  to weaken support post  150  about weak axis W, adjacent to or near grade (when installed). This will accommodate yielding of support post  150  approximately at grade or near grade, allowing support  150  to fracture or otherwise yield at the point of failure.  
      In the illustrated embodiment, weakened section  160  includes a pair of cutouts or notches disposed in opposing sides of support post  150 . Specifically, weakened section  160  comprises a saw cut that extends inward to form cutouts in opposing sides of support post  150 . In particular embodiments, the saw cut may include a 45 degree notch. However, one of ordinary skill in the art will recognize that notches or saw cuts of other angles may also be employed where appropriate. It will also be recognized by those of ordinary skill in the that the size, configuration, and location of weakened section  160  may be varied significantly within the teachings of the present invention. For example, in addition to or in lieu of saw cuts, weakened section  160  may include one or more circular cutouts similar to those described above with respect to I-beam type support posts. Thus, weakened section  160  may include one or more holes drilled in the longitudinal axis of support post  150 . In other embodiments, weakened section  160  may comprise one or more square, rectangular, triangular, oval, diamond shaped, or other geometric configuration of apertures.  
      By weakening support post  150 , wood posts of greater dimensions may be used than in conventional guardrail systems using unmodified wood posts. As a result, the spacing between support posts  150  may be increased, and less support posts  150  may be required in the cable guardrail system to achieve a desired deflection. Such a design may reduce the costs associated with the installation and repair of the cable guardrail system. Specifically, longer spacing between support posts generally affects the total cost of the cable safety system, not only material, but also installation time and cost.  
      At least three types of guardrail support members are described and illustrated within this specification: (I) S4×7.7 Wide flanges; (II) W6×9 Wide flanges; (III) W8×10 Wide flanges; and (IV) 4×6 wood post. It should be recognized by those of ordinary skill in the art that practically any size, shape, or configuration of guardrail support post may be enhanced by incorporating the teachings of the present invention. Any material including wood, metal, plastic, composite materials, or any combination of these or other suitable materials may be used to form support posts. Additional examples of the types of support posts that may be used may include steel pipe and square tubing. Furthermore, the size, weight and configuration of the support post are just a few factors to be considered to determine the appropriate location of cutouts, to allow yielding along the weak axis, while maintaining sufficient strength along the strong axis to redirect impacting vehicles.  
      Although the present invention has been described by several embodiments, various changes and modifications may be suggested to one skilled in the art. It is intended that the present invention encompass such changes and modifications as fall within the scope of the present appended claims. For example, the features described above may be used independently and/or in combination with each other or other design modifications. Changes in the size or strength of the bolts connecting the cables to the support posts and the hole/slot patterns in the support posts through which these connecting bolts pass may be varied in any manner suitable for enabling the cables to release from the support posts upon impact with an errant vehicle.