 One of the most essential highway safety features is the barrier. Barriers prevent vehicles from crashing into oncoming traffic, from running off bridges, from traveling over cliffs, and from winding up in someone's backyard. The correct installation and maintenance of barriers make invaluable contributions to the total safety system. The Oklahoma Department of Transportation has produced several tapes which can tell us about barriers. Let's take a look at the first one, and I'll be back again at its close. Traffic barriers are key elements in our effort to design and build the safest highways possible. Like most other highway safety devices, traffic barriers are usually of only passing interest to motorists. That is, they're a passing interest until someone hits one. Then they become objects of primary interest, life and death interest. How well they work determines whether or not the motorist is seriously injured or killed. Construction, maintenance, and repair crew people need to know how to correctly install, maintain, and repair these systems so that they can work as well as they were designed. This series of five programs outlines the general procedures that must be followed with the most commonly used roadside barriers, median barriers, bridge rails, and end treatments. Each program of the module describes how the various highway features work, why they're used, and what factors to look for that might cause them to fail. The programs also give examples of how the different systems are initially installed, then maintained and repaired. The first of the five programs discusses the cable barrier system. Program two of the series concentrates on the box beam week post system. Program three covers strong post systems, the W beam rail on steel or wood posts. Program four discusses the installation, maintenance, and repair of the concrete barrier, both at standard section and the various end treatments used with the system. In the final program, the installation, maintenance, and repair of various kinds of end treatments are reviewed. The program highlights these different designs, the breakaway cable terminal, the flared and buried end, the twisted and turned down end, the sentry system, earth berms, and crash cushions used as end treatments in different situations. Before discussing these programs, let's review the general purpose and function of barrier systems. Webster's dictionary defines a barrier as an obstruction, anything that hinders or blocks. Basically, that's what we expect traffic barriers to do, to block or prevent a vehicle from running into a more hazardous object. In a government manual commonly known as the Ash Toe Barrier Guide, definitions of the three basic types of traffic barriers are given. A roadside barrier offers protection from one side only and applies to roadside hazards. A median barrier gives protection from both sides and applies to the separation of opposing traffic. Bridge rail barriers provide protection from one side only and are used to keep the vehicle from going off the bridge. They may be used occasionally to protect pedestrians from vehicular traffic. Traffic barriers are classified according to their stiffness. They're identified as flexible, semi-flexible, or rigid systems. Traffic barriers have three parts, each designed to do a different job. These parts are the end section, the standard section, and the transition section. To function properly, these individual parts must work together as a complete system. Traffic barriers are carefully tested and evaluated before they're approved for use on the highways. But even though a barrier system has been accepted as a standard construction item, its performance will be affected by the way it's installed and maintained. And that's where you, your skills, and these five programs come in. The programs will review the factors that determine whether or not these barriers can work as they should. Have you ever wondered at the end of the day if the traffic barrier you installed was done properly? Well this series of programs will provide the information you need to be sure that you've done a good job. Before viewing these programs, it's important that we review some of the basic factors that can affect traffic barriers. Traffic barrier selection, meaning the choosing of one particular system to meet a specific safety need at a certain location, depends on four things. One, the type of hazard requiring a barrier. Two, the distance from the barriers to the hazard. Three, the distance from the barrier to the flow of traffic. And four, the cost and required maintenance of the system. These factors can change quickly along the roadway. So the type of barrier selected generally fits the prevailing kinds of hazards and their locations, as well as the kinds of vehicles using the road. Obviously the kind of hazard will largely determine the type of system selected to provide the necessary protection. For example, the barrier required for a rigid bridge pier would be different from one needed for a steep embankment. The barrier must be capable of retaining, decelerating and redirecting a vehicle in such a way that no serious injury or death occurs to the passengers. When selecting and installing a barrier, it's very important that it be placed on relatively level ground. The cross slope of the area in front of the barrier should not be steeper than 10 to 1 and curbing must not be installed in front of the barrier. Either of these conditions could cause a vehicle to vault over the barrier instead of striking it at the proper height. If vaulting occurs, the system is failed. If the system fails, death or injury will likely follow. The distance from the barrier to the hazard is important. If the barrier deflects inward all the way to the hazard, it obviously will not provide much protection for the motorist. The distance from the barrier to the outside lane of traffic is also important. A barrier must not be installed so close to a traffic lane that an impacting vehicle could be redirected back into the traffic flow, or the barrier itself be deflected into the normal traffic lane. Finally, the required maintenance and the cost of the system need to be considered when selecting a traffic barrier. In general, flexible systems that are more forgiving when they're hit are best for the driver. But unlike the more rigid systems, flexible barriers receive more permanent damage with each impact and cannot sustain repeated hits without immediate repair. The trade-off is to use flexible systems where they can be set away from the roadway and not be hit so often. Semi-flexible and rigid barriers, which are less susceptible to damage, can be placed closer to the roadway. This strategy balances safety and maintenance costs. Now that you've completed this overview of traffic barriers, please continue with the remaining programs. They review the standard procedures for installing and repairing the steel cable, box beam, W beam, and concrete barrier systems. When you finish the series, you'll know what each system is and is not expected to do. And you'll know what to look for when you install, maintain, or repair a barrier. Sometimes, when you're out on the road dodging traffic, it's easy to forget how important your job really is to those who travel the highways in your work area. Lives are literally in your hands. The wrong flair on an end treatment. Posts that are spaced incorrectly. Guard rail that's set too high or too low. Bolts that are missing from a splice. A cable that isn't tight enough. All these little things can cause a traffic barrier system to fail. It's not stretching the point to say that you could personally save a life by paying attention to the details of your work. For the sake of all highway users, including your own family and loved ones, learn from these programs and apply what you learn in the field. The reward is beyond measure. This overview of barriers helped us see how barriers work in general. In this next tape, we'll look in more detail at the different types of barriers, as well as the different parts of barriers. You'll learn first about the W beam wood and the W beam steel strong post systems. Then, you'll see how the three sections of barriers, end treatments, standard sections, and transition sections should be maintained. The technology of highway safety equipment increases in complexity. The people who install, maintain, and repair these systems must be kept informed of the new technology. This program will help you stay informed by providing the general knowledge that's needed to properly install, maintain, and repair the W beam steel strong post system, or the W beam wood strong post system. More specific instructions concerning installation, maintenance, and repair of strong post systems should be provided through individual state standards. However, this program will help you understand why these systems were developed, how they work, and what can prevent them from working as they were designed. First, let's review the major functions of the two systems. W beam strong post systems are semi-flexible traffic barriers that are designed to stop, slow, or redirect any vehicle that hits them. The barriers are made up of three basic parts, an end treatment, a standard section, and a transition section. All three components are required to make up a system. How these parts are individually designed will depend on the terrain and location of the hazard. The end treatment does two major things. First, it anchors the entire system at each end of the barrier. Secondly, it protects any impacting vehicle from the more rigid sections of the barrier. End treatments come in a variety of shapes and sizes depending on the requirements of the system. They may be built to fall down on impact or to absorb the full force of a head-on hit by pocketing and retaining the car. To a lesser degree, this is also true of the standard and transition sections of these systems. The standard section of a strong post system is usually not hit head-on. It's normally hit at an angle and must be strong enough to deflect the vehicle and redirect it away from hazardous conditions. The effectiveness of the standard sections in a barrier system is influenced by the system's length, how the standard section is attached to the rest of the system, the height of the barrier, the roughness and slope of the terrain, and the rail tensile strength. The purpose of the transition section for most strong post systems is to provide a smooth, continuous change from one type of barrier system to another. This section may also function as either the upstream or downstream anchor of the system to a bridge. The transition section is designed to gradually increase in stiffness as it goes from the flexible guard rail to the rigid bridge rail. It is stiffest at the bridge end to allow less deflection at this critical point in the system. The stiffness prevents the impacting vehicle from forming a pocket in the guard rail and hitting the bridge end. The transition forms a smooth flair in the rail from the flexible section to the rigid section. It's necessary to maintain a level barrier height through transition areas to ensure a smooth progression or change from one barrier to another. Now let's get into a general review of installation maintenance and repair procedures. The W-beam steel strong post system uses a six-foot-long steel wide-plange beam as the post that supports a rail of 12 gauge corrugated steel. The rail is blocked out from the post. The standard rail length is 13 and a half feet with splice connections overlapping every 12 and a half feet. One of the most important safety features of this system is found at the splice connection. All eight bolts must be used to provide enough strength at the splice joint. Fewer bolts will produce weak splices that can easily separate when the rail is hit by a car traveling at normal highway speed. A single 5 eighths inch diameter button head bolt located in the center valley of the W-beam is used to connect the rail to the block and the posts. Some states use a rectangular flat plate washer with the button head bolt to prevent it from pulling through the face of the rail. However, washers should not be used in the standard sections of the strong post systems. The offset block or block out sets the rail six inches out from the face of the post. Many early guard rail designs were not blocked out and this caused some problems. When a vehicle hits a rail that is not blocked out, the impact will often flatten the rail. Instead of sliding along the face of the rail, the vehicle will penetrate beneath it, snag a wheel on a post and spin out onto the roadway. The addition of the block out will help prevent this problem in most situations. A 12 inch long section of 12 gauge W-beam rail is placed behind the rail at each post where a splice does not occur. This piece of W-beam acts as a backup plate and prevents the rail from being cut on the edge of the post. If the rail should be cut this way, large segments of the barrier system would lose tensile strength and fail to function properly. The separated ends of the rail could even spear the impacting vehicle. Backup plates are not needed at splice connections because the overlapping rail provides a double thickness. In the W-beam wood strong post system, the same type of rail, a 12 gauge W-beam, is carried on wooden posts and is blocked out. While similar to the steel strong post system, there are important differences. First of all, the rail is connected by a single 18 inch bolt that passes through the block out and the post. This bolt is much longer than the one used in the steel post system. Distances from the top of the block out to the top of the post may vary from state to state. Previously, a flat plate washer was used on the face of the rail. However, experience has shown that this washer is not needed. A round washer is used under the nut that fastens the bolt to the back of the post. Since there's no tendency for the rail to be cut on a wood block out, no backup plates are required. One or two nails toenailed through the block out into the post will keep the block from swiveling on the single bolt connection. Sometimes a hole is drilled through the block out to prevent it from splitting later on. Keeping the block out in place is obviously important. It has to be lined up with the post to properly support the guard rail. Although mounting height standards vary from state to state, most use standard six-foot steel or wood posts and mount the guard rail at a height from 27 to 30 inches. This height allows three feet of soil support for the post. Now that we've reviewed basic installation, let's check some things you should look for when doing routine maintenance. When inspecting ended treatments, examine existing hardware like bolts, washers and clips for signs of damage. The key to the effectiveness of the end treatment is its anchor to the footing in the ground. All cables must be properly attached and tensioned. These inspection points are critical. The standard section makes up the longest part of the barrier and should be inspected as closely as the other sections since it is the part of the guard rail that absorbs most of the impacts. Here are some questions to ask when you check it out. Are the posts properly embedded? Is there enough soil behind the post to prevent them from being pushed out on impact? Is the height of the barrier correct? Is it consistent through the system? A range from 24 to 30 inches to the top of the rail is a common requirement. Is the rail face smooth? Are splices lapped in the direction of traffic flow? Are post connections properly installed and tight? And finally, do the rail support posts or other elements to prevent any signs of corrosion or damage? If so, have you taken corrective actions? Transition sections of W-Beam Strong post systems are usually easy to inspect. Make sure that all connections are correctly installed. Transition sections bolster into loosen where guard rail and bridge railings join make certain they're tight. Check to see that the section is properly stiffened. Is the flare rate smooth and without projections that could snag a vehicle? Is the beam installed properly? Or the required extra posts correctly installed? Where weakness is present, a section of Thrive-Beam rail may be needed to make the rail stiffer. Like the other barrier sections, see that the transition section is free from curbs, abutmed ends or other obstacles that might vault, snag, or tumble a vehicle. The height of the transition section barrier is very important. It must be correctly positioned at each end to match the height of the barrier it will connect to. The different systems around the country may vary, however basic repairs are the same. The following repair crew demonstrates their technique on this W-Beam Strong post system that's done its job and it's now up to them to put it back in service. Upon arrival at the work site, the first order of business is to set up a traffic control safety zone. The crew begins the repair work by first loosening the connecting nuts and bolts of the damaged system. After the nuts are taken off, the damaged guard rail can be removed. Care must be used at this point. Kinked or bent guard rail must be cautiously removed. Railing that is distorted with bows or kinks can build up a lot of internal tension. When the railing is pulled free, it can spring back and injure someone. When all of the guard rail has been taken from the posts, it's set aside until cleanup. Whatever can be salvaged is set aside for later use with the system, but bent pieces aren't used until they've been straightened. When the work site is cleared of damaged rail, the damaged posts are removed. Wood posts may have to be dug out or pulled out with a chain and hoist. Steel posts that have been slightly twisted can often be straightened in the ground. At this point, the post hole needs to be cleaned up and adjusted to proper depth. Next, place the posts and attach the block out and, if needed, backup plates. A tape measure or string line is used to adjust the post to their proper position. The crew next begins hanging the guard rail. It's more convenient to start the new guard rail from the downstream end of the system since the rail is to overlap in the direction of the flow of traffic. A drift pin can be used to line up the holes in the guard rail and posts as the rail is being hung. Nuts and bolts should only be finger tightened at this point. Backfill and tamp the soil around the base of the post until they're firmly embedded in the ground. If the posts are near a slope, there must be a minimum of two feet between the post hole and the top of the slope. When all the W beam has been hung, all the nuts and bolts should be firmly tightened. And, where needed, toenail the wood post. Finally, when all the repair steps have been completed, the work area should be cleaned up and the elements of your safety zone removed. Remember, in all repair or installation work, be sure to follow your state's guidelines. The W beam wood and steel strong post systems, widely used as a protector for our nation's highway users. The satisfaction of a job well done has special meaning to most phases of our work. Because safety is our work, we can all take satisfaction in knowing that doing the job well helps save lives and decrease injuries. This next video continues the description of the different types of barriers with the box beam barrier system. Although box beam barriers are used in only a few states, we still need to review the unique aspects of this system. In this program about the box beam barrier system, we'll review some of the basic considerations about its use on our nation's roads and highways. Variations of this traffic barrier system are used both as roadside and as median barriers. Their purpose is to slow, stop, and redirect cars that hit them and to reduce the risk of death or serious injury to the passengers. The box beam system normally has three basic elements of a traffic barrier system. End treatment, standard section, and transition section. The box beam works by allowing the rail to disengage from the support post when it's hit. The posts are knocked out of the way by an impacting vehicle, and the railing does the actual work of slowing, stopping, and redirecting the car. Of course, this action depends on the rail being properly anchored by the end treatment or the transition section. Without this anchoring, the system would fail. The strength of the box beam system also depends on the rail splices. Two three-quarter inch by eight inch long bolts are used at each connection. A special feature of the box beam is that its open design allows snow to blow through. This is an important maintenance consideration in locations that are subject to heavy snowfall. The box beam carries the load of an impacting car on its railing. It's set at a standard height of 27 inches to the top of the rail for roadside barriers and 30 inches for median barriers. It will normally deflect from three to five feet and as much as seven feet when it's hit. This amount of deflection must be considered when the box beam is being installed near a physical object that presents a hazard. The hazard must be located a sufficient distance from the barrier so that the barrier will not deflect into the hazard or penetrate into the normal flow of traffic. If the hazard is only a foot or so behind the railing, a car that hits the barrier will also run into the hazard. Another kind of barrier system or a crash cushion would be more appropriate at such a location. As with other systems, the slope of the ground leading up to the barrier should be no more than a 10-foot run to a 1-foot rise or fall. Also, the approach area should be free of curbs and other obstacles. These obstacles may defeat the purpose of the barrier before it can be used. A car out of control might vault over or submarine under the rail if it were to crash into a system that is not placed on flat terrain. The design of the end treatments and transition sections will depend on the unique conditions of each site where the system is located. Especially grading the site or adding crash cushions to the design could make an end treatment safer. Crash cushions of various kinds are especially suitable for end treatments used with median traffic barriers. The same thing may be true for transition sections if they present problems that the standard installation techniques can't solve. For example, there might be a need to add more posts to the section if the downstream end of the barrier brings the railing in close to a rigid hazard like a bridge abutment. The main thing that the end treatment and the transition section must do is to anchor the system so that the standard section can do its job when a car hits it. The standard section of the box beam barrier is a spacing of 6 feet 4 inches. Posts are normally 3 by 5.7 inch eye beams with a steel plate footing welded to the base. The railing is held in place by steel offset brackets attached to the post with 3 eighths inch bolts. With secure end anchorages and correct rail installation the box beam barrier should function as designed as long as it's properly maintained and repaired. What kind of maintenance must you perform? Well, it'll depend on traffic conditions in your area and on the local weather. A regular schedule for checking the system is highly recommended. When you check a system, ask yourself some questions about its purpose and condition. Is the barrier really necessary at this location? Could a mistake have been made installing it here in the first place? If it's not required, should it be removed? If it is required, is the barrier at the correct height? Are any of its parts damaged? Is the distance between the railing and the hazard less than the maximum deflection of the system? In other words, would an impacting car be likely to crash into the hazard? Are all rail to post connections installed correctly? Are rail splices tightly joined? Are the posts correctly spaced apart? Is the front approach to the barrier free of obstacles and not too steep? Are repairs to the system required? A preliminary inspection of the site will reveal the replacement parts and tools that you need for the job. Be sure to set up a traffic control zone when you begin the repair work. If you find that the barrier is an old design, advise your supervisor. It may need to be replaced with a more up-to-date system. If moving the barrier to the side will allow you to do a better job, that too should be considered. The box beam system has proven its effectiveness as an operational traffic barrier. When it's properly designed, installed, and maintained, the box beam will do its job very well, saving lives, and preventing serious injury. We have two more barrier systems to study, the concrete barrier and the cable barrier. Each of them will be explained in the two videos that follow. First, we'll look at installation and safety requirements of the concrete barrier. In the 1960s, a new form of traffic barrier began showing up on roads and highways all across the nation. It was the concrete medium barrier, and originally was installed as several types or designs. Today, after considerable research and testing, the New Jersey and the F-shaped barriers are considered to be the most appropriate functional shapes. Although they're classified as rigid barriers, they are semi-rigid when used on a temporary segmented basis and are not firmly anchored to the ground. More and more, they're used for temporary traffic control and repair projects are in similar short-term situations. While there are many highway agencies using concrete barriers, the designs of these barriers all conform to similar specifications and so far as design and strength capabilities are concerned. The concrete barrier should be constructed of reinforced concrete. It comes in two basic forms, precast or cast in place. Precast concrete barrier is very in length, but are normally cast in 8 to 30-foot lengths. Barriers connecting devices for joining the sections have been devised. Generally, the sections are pinned together at each end and may be anchored at the bottom once they're set into place. Cast in place or slip-formed concrete barriers are typically used for permanent installations and are securely anchored to a foundation. The New Jersey configuration of the concrete barrier has proved to be one of the most effective of all the shapes tested. The significant aspects of concrete barriers found during testing were that the break between the two sloped faces should be no greater than 13 inches above the pavement surface, that the overall height should be no less than 32 inches, and that the vertical surface near the base should be no more than 3 inches high. Where pavement overlays of over 3 inches are anticipated, the basic 32-inch height of the barrier should be increased accordingly. If provision is made in the design for raising the entire barrier, it should be adjusted to match the overlay operations. You need to be aware of the importance of maintaining barrier height. Whenever you detect barriers of improper height, point these out to your immediate supervisor. To adjust the vertical height of the barrier, a vertical extension may be added to the top of existing forms. Portable concrete barriers have application at bridge ends and on construction projects. In most states, contractors handle the original installation of concrete traffic barriers. These installations are made following the state's plans. The maintenance and repair of these systems, however, often falls to state highway crews. In such cases, you may be called upon to do required repair. You'll be guided by the original plans and specifications. The reason for such care is obvious. If the system is not installed as originally planned or retrofitted properly to bring it up to standards, then it might not work right and somebody could be seriously injured or killed if their car impacted the barrier. Flare rates for concrete barriers are very critical and must not be exceeded. These rates have been established based on the expected maximum speed of vehicles that might impact the system. The allowable flare rate will depend on whether or not the system is a permanent or temporary concrete barrier. It will increase with the degree of rigidity in the barrier based on expected vehicle impact speed. For instance, for expected vehicle impact speeds of 70 miles per hour, the permanent concrete barrier needs to be flared at 20 to 1. Although all of these considerations have been set down in plans and standards, you are the ones who will either make or break a system through your maintenance and repair activities. Whenever the concrete barrier is to be used, there will be a need to use an end treatment. And again, while the decision may have been made by the design engineers to what end treatment to use, you should be aware of just what treatments are available for use. Most states have devised standards for how to make a concrete barrier end in a cut slope. Also, there are provisions available for attaching a concrete barrier to an existing guardrail and vice versa. Earth berms may be used as a form of end treatment for concrete barriers. Often these berms are specially designed to stay within the criteria for a clear zone, extending up to the barrier itself. Crash cushions are also used as end treatments. Some of those in common use are the MBCT and the great systems. Plus, on double width barriers, the hot grill, high dry, and the inertia sandbarrel systems. An important thing to remember is an end treatment is always required for the concrete barrier system, whether it's used as a roadside, median, bridge rail, or construction area barrier. The concrete barrier does save lives if it's properly constructed and maintained. In this final video, we'll see the cable barrier and how it compares to the ones we've already studied. The functional requirements of this barrier are especially noteworthy. The primary purpose of traffic barrier systems is to save lives and prevent serious injury to motorists whose vehicles impact these systems. The safety engineer has three basic types of barrier systems to choose from. They are the flexible, semi-flexible, and rigid barriers. The choice may be based on the type of hazard, the lateral distance from the roadway to the hazard, or the preference of the highway agency. Cable barriers are designed to either stop, slow, or redirect an impacting vehicle away from a hazard and do so in such a way that neither death nor serious injury comes to passengers in the air and vehicle. It follows then that a major job of the cable barrier system is to keep the crashing car from reaching the hazard. This is where the physician of the hazard comes into play. The closer the hazard is to the flow of traffic, the more resistance to the force of vehicle impact the traffic barrier must have. Barrier resistance is normally controlled by the amount of give or deflection the system has. The more deflection capability a system has, the greater the distance an impacting vehicle will penetrate toward the hazard. Obviously, a barrier that deflects or gives 10 feet will not be of much use if it's set up at a distance of 2 feet from a hazard. So in choosing a cable barrier system to protect traffic from a potentially dangerous situation, the expected deflection and position of the barrier must be considered. The cable barrier system is the most flexible operational traffic barrier system in use on roads and highways throughout the United States today. It is constructed of three three-quarter inch diameter steel cables mounted on weak steel posts by the use of J-hooks. The top cable is set at a height of 30 inches from the ground with the second cable at 27 inches and the third one at 24 inches. When impacted, deflection of the system is usually from 8 to 12 feet. However, deflection may be as much as 17 feet. Post spacing for the cable barrier system is normally 16 feet. Support posts are standard 3 by 5.7 inch steel. The three three-quarter inch steel cables are not blocked out but are supported on steel hook bolts. In the weak post system, the footings are one-quarter inch by 8 inch by 24 inch steel plates welded to the posts and set at a depth of 24 inches into the ground. The cable barrier system does provide a smooth redirection of an impacting vehicle but because of its built-in deflection characteristics it requires a large recovery area. For this reason, locations where it can be used successfully are limited. To reduce the incidence of vehicle impact and maintenance, the system is normally set at least 20 feet from the edge of the roadway. End anchorage for the cable barrier must ensure that the system retains its tensile strength when impacted. The anchorage normally used with the system is the concrete anchor assembly. This anchor is basically a large piece of concrete either precast or poured on site, reinforced with steel bars and equipped with a steel plate to which the three strands of cable are attached. Cable end treatments are generally either spring cable end assemblies also called compensating devices or turn-buckled cable end assemblies. Their use is normally controlled and determined by the length of the cable system being treated. For instance, on cable runs of up to 500 feet a compensating device would be used on one end and a turn-buckle would be used on the other end of each individual cable. For cable runs of over 500 feet and up to 2,000 feet, both a compensating device and a turn-buckle would be used on each end of each individual cable. For cable runs in excess of 2,000 feet, a special lap splice interlacing within the system itself must take place to ensure that the proper tensile strength is maintained throughout the entire cable run. Depending on their intended purpose, cable barriers can either join or be joined by other traffic barrier systems. As with any traffic safety device, cable barriers require correct installation, maintenance and repair if they're to carry out their designed function of protecting the motoring public. Initial installation is carried out following specific site plans and using standard drawings. Field changes or modifications should not be made. Tight cables are important if the system is to work properly. Tables that show just how much tension is required, along with temperature adjustments, must be used when performing installation of the system. The same type of consideration must be given to the initial setting of the anchoring ends of the system. When these anchors are cast in place, they must be allowed a curing period of either 28 days or until they've reached a compressive strength of at least 3,000 psi before any tensile loads are placed on them. As with all other traffic barrier systems, proper site preparation, installation according to designated plans and state standards, maintenance according to specifications and immediate repair when required will result in the cable barrier system being able to prevent serious injury and to save lives on our nation's roads and highways. Together we've seen the four types of barriers, the W beam wood and steel strong post systems, the box beam system, the concrete barrier and the cable barrier. Our study of barriers, however, isn't quite complete. To fully understand the safety features of barriers, we need to look carefully at all three sections that comprise a barrier. This session we've covered only standard sections. In another session, we'll study the end treatments and transitions of barriers. In all our future sessions, we'll continue to explore highway safety features and your role in guaranteeing their effectiveness.