Guardrail System

Abstract

A guardrail system including a sled designed to absorb the impact of a vehicle is disclosed. The sled forms part of the terminal portion of the guardrail system. The terminal portion of the guardrail system also includes one or more cables that are anchored to the ground and pass through the sled. The sled supports a cable break that is in engagement with the cable. The sled is supported by a releasable post that is released from its base upon the impact of a vehicle. The cable or cables extend for some distance from the sled along the guardrail system. Once the post supporting the sled is released from its base due to the impact of a vehicle, the sled can move along the cable with the friction between the cable brake and the cable gradually dissipating the energy from the impact.

1 . An impact absorbing system for use with a barrier positioned proximate a pathway for use by vehicular traffic, the impact absorbing system comprising: 
 a sled;    at least one cable having a portion extending between the barrier and said sled and a portion extending between said sled and a first anchor location proximate the pathway, in use said sled being positioned between the barrier and said first anchor location; and    a cable brake supported by said sled, wherein a portion of said cable passing through said sled and extending at least six inches on either side of said sled follows a non-tortuous path,    whereby when the impact absorbing system is installed proximate the pathway, said sled can move along said cable upon impact of a vehicle on said sled, the vehicle impacting said sled with energy, and with frictional forces between said cable and said cable brake dissipating at least a portion of the energy from the impact.    
   
   
       2 . The impact absorbing system of  claim 1 , wherein for each and every point within said portion of said cable passing through said sled and extending at least six inches on either side of said sled if a direction vector of said cable at a selected end point of said portion of said cable is placed in tip to tale relationship with a direction vector of said cable at a point within said portion of said cable then said direction vector of said cable at said selected end point and said direction vector of said cable at said point within said portion of said cable define an internal angle in the range of 100° to 180°.  
   
   
       3 . The impact absorbing system of  claim 1 , wherein internal angles formed by any bends in said portion of said cable passing through said sled and extending at least six inches on either side of said sled are in the range of greater than or equal to 100° to less than or equal to 180°.  
   
   
       4 . The impact absorbing system of  claim 1 , wherein internal angles formed by any bends in said portion of said cable passing through said sled and extending at least six inches on either side of said sled are in the range of greater than or equal to 110° to less than or equal to 180°.  
   
   
       5 . A guardrail system having an impact absorbing terminal portion comprising: 
 a sled according to  claim 1;     a barrier comprising at least one guardrail post adapted for being fixed to a surface proximate a roadway;    at least one cable having a portion extending between said guardrail post and said sled and a portion extending between said sled and a first anchor location near the surface proximate the roadway, in use said sled being positioned between said guardrail post and said first anchor location; and    a cable brake supported by said sled, said cable brake comprising at least a first brake pad and a second brake pad positioned on opposite sides of said cable, said first brake pad and said second brake pad frictionally engaging said cable in use,    whereby when the guardrail system is installed on a side of the roadway, said sled can move along said cable upon impact of a vehicle on said sled, the vehicle impacting said sled with energy, with frictional forces between said cable and said first and second brake pads dissipating at least a portion of the energy from the impact.    
   
   
       6 . The guardrail system of  claim 5 , wherein said cable brake further comprises a cable brake housing incorporated in said sled, and wherein said first brake pad and said second brake pad are received in said cable brake housing.  
   
   
       7 . The guardrail system of  claim 6 , wherein said cable brake housing has a cable inlet, cable outlet, and opposing sidewall portions that are tapering from said cable inlet to said cable outlet such that said opposing sidewall portions are closer together near said cable outlet as compared to said opposing sidewall portions near said cable inlet 
 whereby as said sled moves along said cable upon impact of a vehicle on said sled, said tapering opposing sidewall portions tend to more forcefully squeeze said first and second brake pads toward one another such that said frictional forces between said cable and said first and second brake pads are increased.    
   
   
       8 . The guardrail system of  claim 7 , wherein said first brake pad has a threaded hole provided at a location that is at spaced separation from a surface portion of said first brake pad that is in contact with said cable when in use, wherein said second brake pad has a threaded hole provided at a location that is at spaced separation from a surface portion of said second brake pad that is in contact with said cable when in use, and wherein said cable brake further comprises: 
 a collar having a first surface facing away from said first and second brake pads when said cable brake is fully assembled, said first surface of said collar declining from either side of said collar toward a centerline of said first surface of said collar such that said centerline of said first surface of said collar is depressed relative to either side of said first surface of said collar with said first surface of said collar sloping forward on either side of said centerline, said collar having an elongated slot extending on either side of said centerline,    a pair of bolts each having a head and a shaft that is threaded at least in part; and    a pair of wedges each having a hole that is sized to provide clearance for said shaft of a respective one of said pair of bolts and said slot being sized to provide clearance for said shaft of each of said pair of bolts and said cable such that said shaft of each of said pair of bolts can pass through said hole of a respective one of said pair of wedges and said slot to engage a respective one of said threaded hole of said first brake pad and said threaded hole of said second brake pad,    wherein when each of said pair of wedges is positioned in contact with a respective sloping portion of said first surface of said collar on either side of said centerline of said first surface of said collar, and when each of said pair of bolts is positioned such that its shaft passes through said hole of said respective one of said pair of wedges and said slot and engages a respective one of said threaded hole of said first brake pad and said threaded hole of said second brake pad, tightening said pair of bolts with said head of each of said bolts being in contact with said respective one of said pair of wedges tends to force said first and second brake pads toward one another such that frictional forces between said cable and said first and second brake pads are increased.    
   
   
       9 . The guardrail system according to  claim 8 , wherein said cable has a longitudinal axis, wherein each of said pair of wedges has a thick side and a thin side, wherein said pair of wedges are positioned on opposite sides of said centerline of said first surface of said collar with said cable passing between said pair of wedges, and wherein each of said pair of wedges is placed in contact with said respective sloping portion of said first surface of said collar with its thick side being positioned closer to said centerline of said first surface of said collar than its thin side such that in operation said head of each of said pair of bolts is in contact with a front surface of a respective one of said pair of wedges that is essentially perpendicular to said longitudinal axis of said cable.  
   
   
       10 . The guardrail system according to  claim 9 , wherein said slot has a widened middle portion through which said cable passes in operation, said widened middle portion having an outline that follows a circular arc on either side of said slot.  
   
   
       11 . The guardrail system according to  claim 5 , wherein the guardrail system comprises a base adapted for being fixed to the surface proximate the roadway, wherein said base comprises a base plate, and wherein said sled further comprises at least one skid plate capable of being supported on top of said base plate for essentially rectilinear movement parallel to said base plate upon impact of the vehicle on said sled.  
   
   
       12 . The guardrail system according to  claim 11 , wherein when in use said base plate is inclined such that it slopes upward in the direction of oncoming traffic.  
   
   
       13 . The guardrail system according to  claim 11 , wherein said base plate is provided with a guide that guides said skid plate during said rectilinear movement of said skid plate relative to said base plate.  
   
   
       14 . The guardrail system according to  claim 13 , wherein said guide is in the form of a channel that receives a portion of said skid plate.  
   
   
       15 . The guardrail system according to  claim 13 , wherein said guide is in the form of opposing channels on either side of said base plate that receive portions of said skid plate on either side of said skid plate.  
   
   
       16 . The guardrail system according to  claim 13 , wherein said guide is in the form of a pocket that receives a portion of said skid plate.  
   
   
       17 . The guardrail system according to  claim 11 , wherein said sled further comprises a beam, said beam has a lower end, said beam supports said cable brake housing and said skid plate is attached to said beam at said lower end of said beam.  
   
   
       18 . The guardrail system according to  claim 17 , further comprising a catch member pivotally attached to said beam such that said catch member pivots about a horizontal pivot axis, said catch member being pivotally movable between a raised position and a lowered position, 
 when said sled is mounted on said base with said catch member positioned substantially on the side of said beam that faces toward oncoming traffic and with said catch member in the lowered position, said catch member has a portion that overlaps at least a portion of said base as seen from the view of oncoming traffic such that movement of said sled relative to said base in the same direction as oncoming traffic would essentially be prevented by interference between said catch member and said base.    
   
   
       19 . The guardrail system according to  claim 18 , further comprising a lever arm attached to said catch member, said catch member being movable between said lowered position and said raised position responsive to said lever arm moving between a first position and a second position such that said catch member moves toward said raised position as said lever arm is moved toward said second position which is closer to said beam compared to said first position, 
 whereby when said sled is mounted on said base with said catch member positioned substantially on the side of said beam that faces toward oncoming traffic and with said catch member in the lowered position and with said cable being in engagement with said cable brake, said lever arm is moved to said second position by a vehicle in the process of colliding with said sled before the vehicle has an impact upon said sled to thereby free said sled for rectilinear motion relative to said base such that said sled can move relative to said base due to the impact energy imparted to said sled by the vehicle and gradually slow down the vehicle.    
   
   
       20 . The guardrail system according to  claim 19 , wherein said catch member comprises two parallel plates that are spaced apart from one another and a catch plate extending between said parallel plates, each of said parallel plates being provided with a hole and with said hole of a first one of said parallel plates being in registry with said hole of a second one of said parallel plates, wherein each said hole in each of said parallel plates is located at spaced separation from said catch plate, wherein the guardrail system further comprises a shaft passing through an opening in said beam and through each said hole in each of said parallel plates to thereby pivotally attach said catch member to said beam, and 
 wherein when said sled is mounted on said base with said catch member positioned substantially on the side of said beam that faces toward oncoming traffic and with said catch member in the lowered position, a portion of said catch plate overlaps at least a portion of said base as seen from the view of oncoming traffic such that movement of said sled relative to said base in the same direction as oncoming traffic would essentially be prevented by interference between said catch member and said base.    
   
   
       21 . The guardrail system according to  claim 11 , further comprising a catch member pivotally attached to said sled such that said catch member pivots about a horizontal pivot axis, said catch member being pivotally movable between a raised position and a lowered position, 
 when said sled is mounted on said base with said catch member positioned substantially on the side of said sled that faces toward oncoming traffic and with said catch member in the lowered position, said catch member has a portion that overlaps at least a portion of said base as seen from the view of oncoming traffic such that movement of said sled relative to said base in the same direction as oncoming traffic would essentially be prevented by interference between said catch member and said base.    
   
   
       22 . The guardrail system according to  claim 21 , further comprising a lever arm attached to said catch member, said catch member being movable between said lowered position and said raised position responsive to said lever arm moving between a first position and a second position such that said catch member moves toward said raised position as said lever arm is moved toward said second position which is closer to said brake housing compared to said first position, 
 whereby when said sled is mounted on said base with said catch member positioned substantially on the side of said sled that faces toward oncoming traffic and with said catch member in the lowered position and with said cable being in engagement with said cable brake, said lever arm is moved to said second position by a vehicle in the process of colliding with said sled before the vehicle has an impact upon said sled to thereby free said sled for rectilinear motion relative to said base such that said sled can move relative to said base due to the impact energy imparted to said sled by the vehicle and gradually slow down the vehicle.    
   
   
       23 . The guardrail system according to  claim 22 , further comprising an impact plate attached to said lever arm.  
   
   
       24 . The guardrail system according to  claim 21 , wherein said catch member comprises two parallel plates that are spaced apart from one another and a catch plate extending between said parallel plates, each of said parallel plates being provided with a hole and with said hole of a first one of said parallel plates being in registry with said hole of a second one of said parallel plates, wherein each said hole in each of said parallel plates is located at spaced separation from said catch plate, wherein the guardrail system further comprises a shaft passing through an opening in said sled and through each said hole in each of said parallel plates to thereby pivotally attach said catch member to said sled, and 
 wherein when said sled is mounted on said base with said catch member positioned substantially on the side of said sled that faces toward oncoming traffic and with said catch member in the lowered position, a portion of said catch plate overlaps at least a portion of said base as seen from the view of oncoming traffic such that movement of said sled relative to said base in the same direction as oncoming traffic would essentially be prevented by interference between said catch member and said base.    
   
   
       25 . The guardrail system according to  claim 24 , further comprising a lever arm attached to said catch member, said catch member being movable between said lowered position and said raised position responsive to said lever arm moving between a first position and a second position such that said catch member moves toward said raised position as said lever arm is moved toward said second position which is closer to said brake housing compared to said first position, 
 whereby when said sled is mounted on said base with said catch member positioned substantially on the side of said sled that faces toward oncoming traffic and with said catch member in the lowered position and with said cable being in engagement with said cable brake, said lever arm is moved to said second position by a vehicle in the process of colliding with said sled before the vehicle has an impact upon said sled to thereby free said sled for rectilinear motion relative to said base such that said sled can move relative to said base due to the impact energy imparted to said sled by the vehicle and gradually slow down the vehicle.    
   
   
       26 . The guardrail system according to  claim 25 , further comprising an impact plate attached to said lever arm.  
   
   
       27 . The guardrail system according to  claim 11 , wherein the guardrail system further comprises at least one guardrail section, wherein said guardrail section has a front side and a back side, wherein said cable has a first end and a second end, said first end of said cable is anchored to the surface proximate the roadway at said first anchor location and said second end of said cable is anchored in place at a second anchor location over said back side of said guardrail section, when the guardrail system is installed on the side of the roadway.  
   
   
       28 . The guardrail system according to  claim 27 , wherein said guardrail section is one of a plurality of guardrail sections included in the guardrail system, wherein at least one of said plurality of guardrail sections is supported at least in part by said guardrail post, wherein each of said plurality of guardrail sections has a front side, a back side, and a cross sectional shape that provides at least one trough on said back side of each of said plurality of guardrail sections, and wherein said second end of said cable is anchored in position in said trough of one of said plurality of guardrail sections, when the guardrail system is installed on the side of the roadway.  
   
   
       29 . The guardrail system according to  claim 28 , wherein said second end of said cable is provided with a threaded shaft that is essentially coaxial with said cable and the guardrail system further comprises: 
 a mounting bracket for attaching one of said plurality of guardrail sections to said guardrail post, wherein said mounting bracket includes at least one sleeve having a bore with a diameter that is large enough to allow said threaded shaft to extend through said bore of said sleeve; and    a threaded nut capable of engaging said threaded shaft, said nut being too large to pass through said bore of said sleeve, said nut engaging said threaded shaft with said cable extending toward said sled on an opposite side of said sleeve relative to said nut to thereby anchor said second end of said cable in position over said back side of one of said plurality of guardrail sections, when said threaded nut is engaged to said threaded shaft and the guardrail system is installed on the side of the roadway.    
   
   
       30 . The guardrail system according to  claim 27 , wherein said guardrail section is supported at least in part by said guardrail post, wherein said guardrail section has a cross sectional shape that provides at least one trough on said back side of said guardrail section, and wherein said second end of said cable is anchored in position in said trough of said guardrail section, when the guardrail system is installed on the side of the roadway.  
   
   
       31 . The guardrail system according to  claim 30 , wherein said second end of said cable is provided with a threaded shaft that is essentially coaxial with said cable and the guardrail system further comprises: 
 a mounting bracket for attaching said guardrail section to said guardrail post, wherein said mounting bracket includes at least one sleeve having a bore with a diameter that is large enough to allow said threaded shaft to extend through said bore of said sleeve; and    a threaded nut capable of engaging said threaded shaft, said nut being too large to pass through said bore of said sleeve, said nut engaging said threaded shaft with said cable extending toward said sled on an opposite side of said sleeve relative to said nut to thereby anchor said second end of said cable in position over said back side of said guardrail section, when said threaded nut is engaged to said threaded shaft and the guardrail system is installed on the side of the roadway.    
   
   
       32 . The guardrail system according to  claim 31 , wherein said base has a base post adapted for being fixed to the surface proximate the roadway to thereby anchor said base to the surface proximate the roadway, wherein said base post has a top, and wherein said base plate is attached to said top of said base post, the guardrail system further comprising: 
 an anchor structure for anchoring said first end of said cable to the surface proximate the roadway at said first anchor location when the guardrail system is installed on a side of the roadway.    
   
   
       33 . The guardrail system according to  claim 32 , wherein said threaded nut is a first threaded nut and said threaded shaft is a first threaded shaft, wherein said first end of said cable is provided with a second threaded shaft that is essentially coaxial with said cable and said anchor structure comprises: 
 an anchor post adapted for being fixed to the surface proximate the roadway, in use said anchor post being positioned upstream of said base post relative to the direction of traffic flow in a lane of the roadway nearest the guardrail system;    a pair of bars extending in parallel between said anchor post and said base post, each of said pair of bars having a longitudinal axis, each of said pair of bars having a first end and a second end, each of said pair of bars being attached to said anchor post proximate said first end thereof, and each of said pair of bars being attached to said base post proximate said second end thereof;    at least one angled plate extending between said pair of bars at a position intermediate said anchor post and said base post, said angled plate having an inclined portion that is angled relative to said longitudinal axis of each of said pair of bars such that in use said inclined portion rises upward relative to the surface proximate the roadway with decreasing horizontal distance from said anchor post, said inclined portion having an opening that is large enough to allow said second threaded shaft at said first end of said cable to extend through said opening of said inclined portion; and    a second threaded nut capable of engaging said second threaded shaft at said first end of said cable, said second threaded nut being too large to pass through said opening of said inclined portion, said second nut engaging said second threaded shaft at said first end of said cable with said cable extending toward said sled on an opposite side of said inclined portion relative to said second nut to thereby anchor said first end of said cable in position at said first anchor location, when said second threaded nut is engaged to said second threaded shaft at said first end of said cable and the guardrail system is installed on the side of the roadway.    
   
   
       34 . The guardrail system according to  claim 33 , wherein said opening in said inclined portion is in the form of a U-shaped slot.  
   
   
       35 . The guardrail system according to  claim 33 , wherein said cable is a first cable, said cable brake is a first cable brake, said sleeve is a first sleeve, and said angled plate is a first angled plate, wherein said mounting bracket includes a second sleeve, and the guardrail system further comprises: 
 a second cable provided to extend substantially in parallel with said first cable, said second cable having a first end and a second end, wherein said second end of said second cable is provided with a third threaded shaft that is essentially coaxial with said second cable, wherein said first end of said second cable is provided with a fourth threaded shaft that is essentially coaxial with said second cable, wherein said second sleeve has a bore with a diameter that is large enough to allow said third threaded shaft to extend through said bore of said second sleeve;    a second cable brake supported by said sled, said second cable brake comprising at least a third brake pad and a fourth brake pad positioned on opposite sides of said second cable, said third brake pad and said fourth brake pad frictionally engaging said second cable in use;    a third threaded nut capable of engaging said third threaded shaft, said third threaded nut being too large to pass through said bore of said second sleeve, said third threaded nut engaging said third threaded shaft with said second cable extending toward said sled on an opposite side of said second sleeve relative to said third threaded nut to thereby anchor said second end of said second cable in position over said back side of said guardrail section, when said third threaded nut is engaged to said third threaded shaft and the guardrail system is installed on the side of the roadway;    a second angled plate extending between said pair of bars at a position intermediate said first angled plate and one of said anchor post and said base post, said second angled plate having an inclined portion that is angled relative to said longitudinal axis of each of said pair of bars such that in use said inclined portion of said second angled plate rises upward relative to the surface proximate the roadway with decreasing horizontal distance from said anchor post, said inclined portion of said second angled plate having an opening that is large enough to allow said fourth threaded shaft at said first end of said second cable to extend through said opening of said inclined portion of said second angled plate; and    a fourth threaded nut capable of engaging said fourth threaded shaft at said first end of said second cable, said fourth threaded nut being too large to pass through said opening of said inclined portion of said second angled plate, said fourth threaded nut engaging said fourth threaded shaft at said first end of said second cable with said second cable extending toward said sled on an opposite side of said inclined portion of said second angled plate relative to said fourth threaded nut to thereby anchor said first end of said second cable in position at a third anchor location, when said fourth threaded nut is engaged to said fourth threaded shaft at said first end of said second cable and the guardrail system is installed on the side of the roadway.    
   
   
       36 . The guardrail system of  claim 35 , wherein said guardrail post is a yieldable guardrail post designed to yield at a predetermined impact force, said yieldable guardrail post comprising: 
 a first elongated member having an elongated back plate and two side plates that are parallel two one another, said side plates projecting at right angles to said back plate on either side of said back plate to thereby give said first elongated member a channel-shaped cross section;    a second elongated member having an elongated back plate and two side plates that are parallel two one another, said side plates of said second elongated member projecting at right angles to said back plate of said second elongated member on either side of said back plate of said second elongated member to thereby give said second elongated member a channel-shaped cross section, said first elongated member and said second elongated member being attached together with their respective back plates in abutting contact so as to form a beam having an H-shaped cross section, said first and second elongated members each having a longitudinal axis, said second elongated member having a slit transverse to said longitudinal axis thereof that transects said second elongated member; and    a reinforcement plate attached to said back plate of one of said first elongated member and said second elongated member proximate said slit in each of said side plates of said second elongated member.    
   
   
       37 . The guardrail system according to  claim 29 , wherein said base has a base post adapted for being fixed to the surface proximate the roadway to thereby anchor said base to the surface proximate the roadway, wherein said base post has a top, and wherein said base plate is attached to said top of said base post, the guardrail system further comprising: 
 an anchor structure for anchoring said first end of said cable to the surface proximate the roadway at said first anchor location when the guardrail system is installed on the side of the roadway.    
   
   
       38 . The guardrail system according to  claim 37 , wherein said threaded nut is a first threaded nut and said threaded shaft is a first threaded shaft, wherein said first end of said cable is provided with a second threaded shaft that is essentially coaxial with said cable and said anchor structure comprises: 
 an anchor post adapted for being fixed to the surface proximate the roadway, in use said anchor post being positioned upstream of said base post relative to the direction of traffic flow in a lane of the roadway nearest the guardrail system;    a pair of bars extending in parallel between said anchor post and said base post, each of said pair of bars having a longitudinal axis, each of said pair of bars having a first end and a second end, each of said pair of bars being attached to said anchor post proximate said first end thereof, and each of said pair of bars being attached to said base post proximate said second end thereof;    at least one angled plate extending between said pair of bars at a position intermediate said anchor post and said base post, said angled plate having an inclined portion that is angled relative to said longitudinal axis of each of said pair of bars such that in use said inclined portion rises upward relative to the surface proximate the roadway with decreasing horizontal distance from said anchor post, said inclined portion having an opening that is large enough to allow said second threaded shaft at said first end of said cable to extend through said opening of said inclined portion; and    a second threaded nut capable of engaging said second threaded shaft at said first end of said cable, said second threaded nut being too large to pass through said opening of said inclined portion, said second nut engaging said second threaded shaft at said first end of said cable with said cable extending toward said sled on an opposite side of said inclined portion relative to said second nut to thereby anchor said first end of said cable in position at said first anchor location, when said second threaded nut is engaged to said second threaded shaft at said first end of said cable and the guardrail system is installed on the side of the roadway.    
   
   
       39 . The guardrail system according to  claim 38 , wherein said opening in said inclined portion is in the form of a U-shaped slot.  
   
   
       40 . The guardrail system according to  claim 38 , wherein said cable is a first cable, said cable brake is a first cable brake, said sleeve is a first sleeve, and said angled plate is a first angled plate, wherein said mounting bracket includes a second sleeve, and the guardrail system further comprises: 
 a second cable provided to extend substantially in parallel with said first cable, said second cable having a first end and a second end, wherein said second end of said second cable is provided with a third threaded shaft that is essentially coaxial with said second cable, wherein said first end of said second cable is provided with a fourth threaded shaft that is essentially coaxial with said second cable, wherein said second sleeve has a bore with a diameter that is large enough to allow said third threaded shaft to extend through said bore of said second sleeve;    a second cable brake supported by said sled, said second cable brake comprising at least a third brake pad and a fourth brake pad positioned on opposite sides of said second cable, said third brake pad and said fourth brake pad frictionally engaging said second cable in use;    a third threaded nut capable of engaging said third threaded shaft, said third threaded nut being too large to pass through said bore of said second sleeve, said third threaded nut engaging said third threaded shaft with said second cable extending toward said sled on an opposite side of said second sleeve relative to said third threaded nut to thereby anchor said second end of said second cable in position over said back side of said one of said plurality of guardrail sections, when said third threaded nut is engaged to said third threaded shaft and the guardrail system is installed on the side of the roadway;    a second angled plate extending between said pair of bars at a position intermediate said first angled plate and one of said anchor post and said base post, said second angled plate having an inclined portion that is angled relative to said longitudinal axis of each of said pair of bars such that in use said inclined portion of said second angled plate rises upward relative to the surface proximate the roadway with decreasing horizontal distance from said anchor post, said inclined portion of said second angled plate having an opening that is large enough to allow said fourth threaded shaft at said first end of said second cable to extend through said opening of said inclined portion of said second angled plate; and    a fourth threaded nut capable of engaging said fourth threaded shaft at said first end of said second cable, said fourth threaded nut being too large to pass through said opening of said inclined portion of said second angled plate, said fourth threaded nut engaging said fourth threaded shaft at said first end of said second cable with said second cable extending toward said sled on an opposite side of said inclined portion of said second angled plate relative to said fourth threaded nut to thereby anchor said first end of said second cable in position at a third anchor location, when said fourth threaded nut is engaged to said fourth threaded shaft at said first end of said second cable and the guardrail system is installed on the side of the roadway.    
   
   
       41 . The guardrail system of  claim 40 , wherein said guardrail post is a yieldable guardrail post designed to yield at a predetermined impact force, said yieldable guardrail post comprising: 
 a first elongated member having an elongated back plate and two side plates that are parallel two one another, said side plates projecting at right angles to said back plate on either side of said back plate to thereby give said first elongated member a channel-shaped cross section;    a second elongated member having an elongated back plate and two side plates that are parallel two one another, said side plates of said second elongated member projecting at right angles to said back plate of said second elongated member on either side of said back plate of said second elongated member to thereby give said second elongated member a channel-shaped cross section, said first elongated member and said second elongated member being attached together with their respective back plates in abutting contact so as to form a beam having an H-shaped cross section, said first and second elongated members each having a longitudinal axis, said second elongated member having a slit transverse to said longitudinal axis thereof that transects said second elongated member; and    a reinforcement plate attached to said back plate of one of said first elongated member and said second elongated member proximate said slit in each of said side plates of said second elongated member.    
   
   
       42 . The guardrail system of  claim 5 , wherein said guardrail post is a yieldable guardrail post designed to yield at a predetermined impact force, said yieldable guardrail post comprising: 
 a first elongated member having an elongated back plate and two side plates that are parallel two one another, said side plates projecting at right angles to said back plate on either side of said back plate to thereby give said first elongated member a channel-shaped cross section;    a second elongated member having an elongated back plate and two side plates that are parallel two one another, said side plates of said second elongated member projecting at right angles to said back plate of said second elongated member on either side of said back plate of said second elongated member to thereby give said second elongated member a channel-shaped cross section, said first elongated member and said second elongated member being attached together with their respective back plates in abutting contact so as to form a beam having an H-shaped cross section, said first and second elongated members each having a longitudinal axis, said second elongated member having a slit transverse to said longitudinal axis thereof that transects said second elongated member; and    a reinforcement plate attached to said back plate of one of said first elongated member and said second elongated member proximate said slit in each of said side plates of said second elongated member.    
   
   
       43 . A yieldable guardrail post designed to yield at a predetermined impact force, said yieldable guardrail post comprising: 
 a first elongated member having an elongated back plate and two side plates that are parallel two one another, said side plates projecting at right angles to said back plate on either side of said back plate to thereby give said first elongated member a channel-shaped cross section;    a second elongated member having an elongated back plate and two side plates that are parallel two one another, said side plates of said second elongated member projecting at right angles to said back plate of said second elongated member on either side of said back plate of said second elongated member to thereby give said second elongated member a channel-shaped cross section, said first elongated member and said second elongated member being attached together with their respective back plates in abutting contact so as to form a beam having an H-shaped cross section, said first and second elongated members each having a longitudinal axis, said second elongated member having a slit transverse to said longitudinal axis thereof that transects said second elongated member; and    a reinforcement plate attached to said back plate of one of said first elongated member and said second elongated member proximate said slit in each of said side plates of said second elongated member.    
   
   
       44 . A releasable post comprising: 
 a base post adapted for being fixed to a surface to thereby anchor the releasable post to the surface, wherein said base post has a top;    a base plate attached to said top of said base post;    a beam having a lower end;    a skid plate attached to said beam at said lower end of said beam;    a catch member pivotally attached to said beam such that said catch member pivots about a pivot axis, said catch member being pivotally movable between a raised position and a lowered position,    when said base post is fixed to the surface, said beam is mounted on said base plate with said skid plate supported by said base plate, and said catch member is in said lowered position, said catch member has a portion that overlaps at least a portion of at least one of said base plate and said base post such that rectilinear movement of said beam relative to said base post in a predetermined direction would essentially be prevented by interference between said catch member and at least one of said base plate and said base post; and    a lever arm attached to said catch member, said catch member being movable between said lowered position and said raised position responsive to said lever arm moving between a first position and a second position such that said catch member moves toward said raised position as said lever arm is moved toward said second position which is closer to said beam compared to said first position,    whereby when said base post is fixed to the surface, said beam is mounted on said base plate with said skid plate supported by said base plate, and said catch member is in said lowered position, an impact on said lever arm that moves said lever arm to said second position frees said beam for rectilinear motion relative to said base post in said predetermined direction.    
   
   
       45 . The releasable post according to  claim 44 , wherein said catch member comprises two parallel plates that are spaced apart from one another and a catch plate extending between said parallel plates, each of said parallel plates being provided with a hole and with said hole of a first one of said parallel plates being in registry with said hole of a second one of said parallel plates, wherein each said hole in each of said parallel plates is located at spaced separation from said catch plate, wherein the releasable post further comprises a shaft passing through an opening in said beam and through each said hole in each of said parallel plates to thereby pivotally attach said catch member to said beam, and 
 wherein when said base post is fixed to the surface, said beam is mounted on said base plate with said skid plate supported by said base plate, and said catch member is in said lowered position, a portion of said catch plate overlaps at least a portion of at least one of said base plate and said base post such that rectilinear movement of said beam relative to said base post in said predetermined direction would essentially be prevented by interference between said catch member and at least one of said base plate and said base post.    
   
   
       46 . The releasable post according to  claim 45 , wherein said base plate is inclined such that it slopes upward in said predetermined direction when said base post is fixed to the surface.  
   
   
       47 . The releasable post according to  claim 45 , wherein said base plate is provided with a guide that guides said skid plate during said rectilinear movement of said skid plate relative to said base plate.  
   
   
       48 . The releasable post according to  claim 47 , wherein said guide is in the form of a channel that receives a portion of said skid plate.  
   
   
       49 . The releasable post according to  claim 47 , wherein said guide is in the form of opposing channels on either side of said base plate that receive portions of said skid plate on either side of said skid plate.  
   
   
       50 . The releasable post according to  claim 47 , wherein said guide is in the form of a pocket that receives a portion of said skid plate.  
   
   
       51 . A guardrail system having an impact absorbing terminal portion comprising: 
 a sled;    a guardrail post adapted for being fixed to a surface proximate a roadway;    at least one cable having a portion extending between said guardrail post and said sled and a portion extending between said sled and a first anchor location, in use said sled being positioned between said guardrail post and said first anchor location; and    a cable brake supported by said sled, said cable brake frictionally engaging said cable in use,    wherein a portion of said cable passing through said cable brake follows a non-tortuous path,    whereby when the guardrail system is installed on a side of the roadway, said sled can move along said cable upon impact of a vehicle on said sled, the vehicle impacting said sled with energy, with frictional forces between said cable and said first and second brake pads dissipating at least a portion of the energy from the impact.    
   
   
       52 . The guardrail system of  claim 51 , wherein said portion of said cable passing through said cable brake has bends such that internal angles formed by said bends of said portion of said cable passing through said cable brake are all obtuse.  
   
   
       53 . The guardrail system of  claim 52 , wherein said internal angles formed by said bends of said portion of said cable passing through said cable brake are in the range of greater than or equal to 110° to less than or equal to 180°.  
   
   
       54 . The guardrail system of  claim 51 , wherein said portion of said cable passing through said cable brake follows a substantially straight path.  
   
   
       55 . A method for providing a guardrail system having an impact absorbing terminal portion on a surface proximate a roadway, the roadway having a lane nearest the guardrail system, traffic in the lane nearest the guardrail system defining a direct of flow of traffic, the method comprising the steps of: 
 providing a base adapted for being fixed to the surface proximate the roadway, the base having a base plate;    fixing the base to the surface proximate the roadway;    providing at least one guardrail post adapted for being fixed to the surface proximate the roadway;    fixing the guardrail post to the surface proximate the roadway downstream of the base in relation to the direction of flow of traffic;    providing an anchor structure;    fixing the anchor structure to the surface proximate the roadway upstream of the base in relation to the direction of flow of traffic;    providing a sled;    positioning the sled on the base plate;    providing at least one cable having a first end and a second end;    anchoring the first end of the cable to the anchor structure at a first anchor location upstream of the sled in relation to the direction of flow of traffic;    routing the cable through the sled;    anchoring the second end of the cable at a second anchor location downstream of the sled in relation to the direction of flow of traffic, such that a portion of the cable extends between the guardrail post and the sled;    providing a cable brake comprising at least a first brake pad and a second brake pad; and    frictionally engaging the first brake pad and the second brake pad to the cable with the first brake pad and the second brake pad positioned on opposite sides of the cable and with the first brake pad and the second brake pad positioned relative to the sled such that the first brake pad and the second brake pad would interfere with movement of the sled toward the guardrail post over at least a substantial portion of a distance between the sled and the guardrail post upon impact of a vehicle on the sled, and    interference with the movement of the sled toward the guardrail post due to the engagement of the first brake pad and the second brake pad with the cable being of such a nature that the sled can move along the cable upon the impact of the vehicle on the sled, when the vehicle impacts the sled with energy above a predetermined threshold level, with frictional forces between the cable and the first and second brake pads dissipating at least a portion of the energy from the impact.    
   
   
       56 . The method of  claim 55 , wherein the cable brake further comprises a cable brake housing incorporated in the sled, and wherein said step of frictionally engaging the first brake pad and the second brake pad to the cable comprises the step of positioning the first brake pad and the second brake pad such that the first brake pad and the second brake pad are received in the cable brake housing.  
   
   
       57 . The method of  claim 56 , further comprising the step of providing the cable brake housing with a cable inlet, a cable outlet, and opposing sidewall portions that are tapering from the cable inlet to the cable outlet such that the opposing sidewall portions are closer together near the cable outlet as compared to the opposing sidewall portions near the cable inlet.  
   
   
       58 . The method of  claim 55 , further comprising the steps of: 
 providing the first brake pad with a threaded hole at a location that is at spaced separation from a surface portion of the first brake pad that is in contact with the cable when in use;    providing the second brake pad with a threaded hole at a location that is at spaced separation from a surface portion of the second brake pad that is in contact with the cable when in use;    providing a collar having a first surface facing away from the first and second brake pads when the cable brake is fully assembled, the first surface of the collar declining from either side of the collar toward a centerline of the first surface of the collar such that the centerline of the first surface of the collar is depressed relative to either side of the first surface of the collar with the first surface of the collar sloping forward on either side of the centerline, the collar having an elongated slot extending on either side of the centerline;    providing a pair of bolts each having a head and a shaft that is threaded at least in part; and    providing a pair of wedges each having a hole that is sized to provide clearance for the shaft of a respective one of the pair of bolts and the slot being sized to provide clearance for the shaft of each of the pair of bolts and the cable such that the shaft of each of the pair of bolts can pass through the hole of a respective one of the pair of wedges and the slot to engage a respective one of the threaded hole of the first brake pad and the threaded hole of the second brake pad;    positioning each of the pair of wedges in contact with a respective sloping portion of the first surface of the collar on either side of the centerline of the first surface of the collar;    positioning each of the pair of bolts such that its shaft passes through the hole of the respective one of the pair of wedges and the slot and engages a respective one of the threaded hole of the first brake pad and the threaded hole of the second brake pad; and    tightening the pair of bolts with the head of each of the bolts being in contact with the respective one of the pair of wedges to force the first and second brake pads toward one another such that frictional forces between the cable and the first and second brake pads are set at a predetermined level.    
   
   
       59 . The method according to  claim 58 , wherein the cable has a longitudinal axis, wherein each of the pair of wedges has a thick side and a thin side, wherein said step of positioning each of the pair of wedges in contact with a respective sloping portion of the first surface of the collar comprises positioning the pair of wedges on opposite sides of the centerline of the first surface of the collar with the cable passing between the pair of wedges, and such that each of the pair of wedges is placed in contact with the respective sloping portion of the first surface of the collar with its thick side being positioned closer to the centerline of the first surface of the collar than its thin side, and such that in operation the head of each of the pair of bolts is in contact with a front surface of a respective one of the pair of wedges that is essentially perpendicular to the longitudinal axis of the cable.  
   
   
       60 . The method according to  claim 59 , further comprising the step of providing the slot with a widened middle portion through which the cable passes and with the widened middle portion having an outline that follows a circular arc on either side of the slot.