 Cable guard rails are one of the oldest types of traffic barriers in use today. Some of the first guard rails installed on roadways in the United States used cables mounted on wood posts. Wood posts began to be replaced by concrete posts and cold rolled steel sections. These in turn were replaced by hot rolled steel eye sections, the first modern cable guard rail systems. This videotape will show the results of recent research efforts to improve the performance and decrease the cost of cable guard rail systems. There are a variety of advantages to using cable systems rather than other types of guard rails. They are easy to install and cost about one third as much as typical strong post W beam guard rails. The large deflection characteristic of cable guard rails can be advantageous where there is adequate area behind the guard rail. Large deflections cause the impact to be softer and therefore less harmful to occupants. Cable systems can be more aesthetically pleasing than typical W beam or Thri-Beam guard rails since they do not obstruct the view. The slender cross section is also an advantage in snowy regions of the country. W and Thri-Beam guard rails can act like snow fences causing a large pile of snow and ice to accumulate along the barrier. The accumulation from windblown snow or snow plowing can prevent the barrier from performing correctly and can also cause snow to drift onto the highway. Cable systems offer very little resistance so most windblown and plowed snow will pass through the cables without accumulating. Low installation and maintenance costs. Reduced impact severity. Wind profile and resistance to snow drifting are characteristics that can make cable guard rails an attractive alternative in many situations. Although there are a variety of cable guard rail systems in use today, they all share a number of similar characteristics. The AASHTO roadside design guide designates the most common cable system as the G1 guard rail. It was developed by the New York Department of Transportation in the early 1960s. When correctly used in appropriate sites, the G1 guard rail has proven to be a very forgiving barrier system. The G1 consists of three cables. J-bolts for attaching the cables to the S3 by 5.7 steel posts. A concrete anchor and hardware for attaching the cables to the anchor block. In recent years, several variations of the basic G1 guard rail have been developed that reduce the cost and enhance the performance of cable guard rails. The state of South Dakota has developed a cable guard rail that is similar to the G1 system except that a smaller, less expensive post is used. The flanged channel post used in the South Dakota system weighs only four pounds per foot, 40% lighter than the standard S3 by 5.7 post. A flanged channel post and soil plate made of re-rolled rail steel would cost about half as much as the standard G1 post in soil plate. The South Dakota cable system cost almost $1 per linear foot less than the G1 guard rail. In this test of the South Dakota system, the cables wrap around the front corner of the small car when it hits the barrier. The cable slips off the post ahead of the collision and the posts either snap off or bend over as they're struck by the car. The cables redirect the car parallel to the barrier. It comes to a controlled stop after braking. In another test, this large car travels about 12 feet past the barrier line before being redirected parallel to the guard rail. The performance of this system is similar to the G1 cable guard rail system. The location of the guard rail on slopes is an important design consideration. If the guard rail is located on the slope, but too close to the edge of the pavement, the cables may contact the vehicle below the front bumper, allowing the car to ride over the cables and penetrate the barrier. If the guard rail is placed at least 18 feet away from the pavement, the vehicle has more time to stabilize before it strikes the cables. In this test, the vehicle suspension had returned to its normal position when the car struck the cables. The cables wrapped around the car just above the front bumper, allowing the guard rail to redirect the vehicle. This cable guard rail transition to a bridge rail is unsafe because it would redirect the vehicle into the rigid end of the bridge. When two longitudinal barriers with different stiffnesses are joined, there must be a smooth transition to avoid pocketing accidents. A transition between a three-cable guard rail and a W-beam guard rail was developed to solve this problem. The post-spacing of the cable system is reduced near the transition, and the cables are passed over and under the W-beam to a concrete anchor buried behind the W-beam's breakaway cable terminal. The large car strikes the cable system and deflects about four feet before it strikes the end of the breakaway cable terminal. The vehicle quickly redirects after striking the W-beam system. Steel is not the only material that can be used for posts. Cable guard rails with wooden posts have been used by some states for decades. Recent tests evaluated a modification of the Minnesota State Standard Design that uses a five-and-a-half inch diameter post. With a one-and-a-half inch hole drill through it, five inches below the ground. This hole helps to weaken the post in the longitudinal direction, ensuring that it breaks away when hit head-on. The post-spacing used is 12 feet 6 inches rather than the 16 feet as is typical for G1 systems. This small car was successfully redirected without exceeding the allowable occupant response values. The system was also strong enough to contain and redirect this large passenger sedan. The maximum barrier deflections were comparable to the standard G1 system in these two tests. As with all types of longitudinal barriers, designing effective end treatments for cable guard rails has been a difficult problem. Vehicles tend to stay in contact with cable guard rails longer than other barrier systems. This is generally desirable, but as posts are weakened to soften the impact, the cable anchor takes more and more of the impact load. If the anchor is too strong, it may not break away if a vehicle strikes it. When an impact occurs near the end of the guard rail, the vehicle can wedge under the sloping anchor cables, causing the vehicle to roll over. When this same problem was recognized for both the standard G1 design and the flange-channel post design, the state of New York set out to develop an alternative anchorage. The result is a modified terminal consisting of a concrete anchor. An attachment bracket and a slip-based post. The cables pull free from the slots in the bracket during an impact. The whole anchorage assembly is flared back from the roadway to reduce the chance of a direct collision. In this test series, a small car ran over the anchorage in both directions without being tripped. The performance of the improved anchor was much better than the original design. The improved terminal was also strong enough to provide adequate anchor strength in this large car test. Although these collisions are still severe, this anchor design appears to be the only cable terminal that does not cause small cars to roll over when the impact occurs near the end of the guard rail. While cable systems are often used on major highways, their reduced cost makes them particularly appropriate for low-volume, low-speed, rural roadways. Even the inexpensive G1 guard rail shown here may not be cost-effective on some low-volume rural roadways. Several new, less costly variations of the cable system were developed in a recent NCHRP project for application on roadways that might not warrant more expensive systems. These new cable guard rails were tested using different speeds, angles, and vehicles than the optional lower service level test recommended in NCHRP Report 230. These systems used two rather than three cables, with the higher cable mounted 27 inches above the ground. Three different types of posts were used in the crash tests. The S3x5.7 post, the Flange Channel post, and the Round Wood post. All three systems performed satisfactorily, deflecting between six and eight feet behind the barrier line. The Flange Channel posts tended to fracture easily, and some were thrown back into the roadway. The cable in the Flange Channel post system rode over the top of the vehicle, so its performance was considered acceptable, though not desirable. Information on these cable guard rails and warrants for their use have been developed in NCHRP project 22-5A. These systems could provide a cost-effective guard rail on lower service level highways that would not otherwise be protected. When used at appropriate sites, cable guard rails have significant advantages over other types of guard rails. Low cost, easy maintenance and installation procedures, resistance to snowdrifting, and aesthetic appeal make cable guard rails an attractive option for many transportation agencies.