 Hello, I'm David DuBois, and this is the first videotape in a series that explores how highway safety features function. Together we'll be learning why the installation and maintenance of safety features must adhere to and even enhance the design. Sometimes when you're in the field and a barrier or other safety feature needs repair work, it seems only common sense to complete the work in the fastest and most economical way possible. Now, while this thinking probably applies to many situations in life, it isn't the best way to do the job in highway work. The purpose of these videos is to show you how safety features are supposed to function. Once you understand what the safety features are intended to do, you'll be able to install and repair them so that their function is not lost. You'll know, for example, that sand-filled barrels must be precisely placed for them to work. You'll also know that barrier end treatments must be anchored securely. And you'll know that the angle of ditch slopes must be determined in relationship to the shape of the floor of the ditch. Not knowing the purpose of the safety feature is very dangerous. If you don't know how a breakaway signpost works, you might repair it in a way that makes it incapable of breaking. The safety of millions of travelers depends on your knowledge. It's up to you to determine how the design should be implemented in the field and how it should be repaired to keep it working as intended. After all, the major goal in the design, construction and maintenance of highways is the reduction of the number of accidents, fatalities and injuries. Know that you can help in meeting this goal. You'll study current principles and practices, not theories. Each session of this course is designed to focus on one safety feature so that you understand its function and its needs for installation and maintenance. We'll begin our study with the clear zone, the area on the side of roadways that gives drivers a place to recover control of their vehicles without fear of hitting something or of losing control of their vehicle. First, we'll watch this video and I'll be back at the end of it to tell you more about the clear zone. Collisions with fixed objects account for nearly 30% of all fatalities in motor vehicle traffic accidents. The fixed objects struck most often are trees, utility poles and guard rails. The people involved could be your friends, your neighbors or even your family. Often these people run off the road because of conditions beyond their control such as bad weather. The actions of another driver could force them off the road. The clear zone provides a safe hazard-free area which will allow a driver who has run off the road to come to a safe stop without being severely injured or killed in a collision with a fixed roadside object. The development and use of the clear zone concept has dramatically reduced the number and severity of fatalities and injuries on urban and rural highways. It is important to note that the clear zone does not have a fixed width of 30 feet but a variable width dependent upon vehicle speed, design traffic volumes and the flatness of the cut or fill side slope. The roadside design guide provides information for determining the minimum clear zone widths for specific conditions. For a 6 to 1 fill slope at 60 miles per hour with an average daily traffic volume of 6,000 vehicles, the clear zone width is approximately 30 feet. On a roadway section with fill slopes between 4 to 1 and 3 to 1, a clear zone must be provided at the toe of slope. Vehicles encroaching on a 3 to 1 slope can be expected to travel to the bottom of the slope before stopping. Horizontal curves also affect the amount of clear zone width needed. The clear zone width should be increased on curved sections where accident history or the potential for accidents indicate a need. Proper pavement super elevation in a horizontal curve will also increase the roadway safety. Clear zones are effective on both high volume freeways and low volume roads. It is important to provide a safe recovery area along all roadways. In certain types of terrain, it may not be cost effective or practical because of environmental impacts to provide the desired clear zone width. In these areas, a thorough analysis of accident history and potential as well as on-site inspections should be conducted to identify safety problems which will require clear zone improvements. If the desired clear zone width cannot be established, the second best alternative is to make the roadside as forgiving as possible. Protect fixed objects such as signs and luminaires using breakaway devices. Remove trees and utility poles in hazardous locations. The last alternative should be installing a guardrail or a crash cushion to prevent vehicles from striking the object. Remember, traffic barriers themselves can be a hazard and should only be used as the last alternative. The clear zone that is provided by design must be maintained after construction is completed. Some seemingly minor changes can make a huge difference in the effectiveness of the clear zone. For instance, if this slope was changed so that its hinge point became sharp instead of gently rounded, a vehicle running off the road could become airborne at the slope break and might roll over instead of safely recovering or traveling to the bottom. Within the ditch line or on the side slopes, small pipe culvered in should be tapered to match the shape of the side slope to allow a safe traversal by errant vehicles. Large pipe culvered-ins or box culvered-ins should not only be tapered to match the side slope but should also be fitted with a grate for safe traversal. Embankment slopes at right angles to traffic are roadside obstacles. They are created by median crossovers, driveways, or intersecting roads. These slopes are dangerous because they can be struck head-on by run-off-the-road vehicles causing the vehicle to become airborne and depending on the steepness of slope and vehicle speed to cause the vehicle to flip over. A flat 10-to-1 slope is desirable and a 6-to-1 slope is acceptable for allowing safe traversal. Don't forget the drainage culvert located in these embankments along the ditch line. The culvert-in should be tapered to match the slope and have a grate to allow the vehicle to cross it easily. Erosion of the side slopes can also reduce the effectiveness of the clear zone. Erosion such as this can easily cause a driver to lose control of his vehicle resulting in an accident. Routine maintenance should include monitoring and controlling erosion, particularly where an unsafe pavement edge drop-off has developed. When construction or maintenance work is being performed on a roadway open to traffic, vehicles and equipment not in use should be stored outside of the clear zone or properly shielded behind portable crash cushions or existing guard ring. Short-term work areas or moving operations should be shielded by truck-mounted attenuators. Even breakaway signs, luminaires and other devices should not be located in the bottom of a ditch or close to the travel lanes. The ditch will tend to direct an errant vehicle along its link and into the sign or pole. These poles should have been placed on the back slope at the far edge of the clear zone or on a concrete median barrier where they are less likely to be hit. In the case of mailboxes, banjo mounts like these should be used. Sign height is also important. Breakaway signs that are not mounted at the proper height may not react as intended upon impact and might penetrate a windshield. Breakaway control and breakaway devices such as signs and luminaires should be routinely inspected for obstructions of visibility, corrosion or damage that could impair the proper functioning of the device and soil erosion around the foot which would cause the breakaway base to stick up higher than the allowed four inches. This could allow impact at an improper height. Slip-based maintenance should include loosening and re-tightening bolts to the correct torque. Over tightened bolts will prevent the base from releasing as it should on impact. Use a calibrated torque wrench where wind loading is a problem. Don't over tighten bolts. Use a thin keeper plate to prevent a sign from walking off its slip base. A uniform acceptable clear zone width should be established for a highway corridor. Fence posts and naturally occurring items such as trees, large shrubs and rocks should not remain within this established clear zone width. Under certain conditions, wholesale removal may not be practical. Selective removal based upon environmental impact studies and accident history may be more pragmatic and acceptable. Landscaping and highway beautification must not conflict with clear zone safety. Trees and shrubs which are small when planted can grow to become safety hazards within the clear zone. Shoulders and slopes should be routinely inspected and cleared of saplings. All natural objects should be treated carefully with safety as the first concern. The roadside barriers and crash cushions that shield the traveling public from rigid obstacles in the clear zone must be routinely inspected to ensure they will function effectively. Cushions should be routinely inspected for damage and vandalism. Most crash cushions must be repaired and rebuilt in accordance with manufacturer specifications. Severe hits sometime require more than just pulling the system out and replacing disposable materials. Hydrocell crash cushions and older G-R-E-A-T systems can be retrofitted with new hex foam cartridges to improve their performance. The cartridges make them easier to maintain and provide safer conditions by limiting the amount of debris flung into the roadway upon impact. In cold weather regions, hydrocells need an antifreeze. A premixed salt solution or ethylene glycol are equally acceptable. During cold weather, moisture in sand barrels can freeze the sand into a solid mass, thereby changing a safety device into a hazard. Barrels should be sealed and checked regularly for required maintenance. Antifreezes should be tested for compatibility with local sands. Some, like calcium chloride, have been known to cement the sand. Roadside barriers should be checked for erosion around the post and in treatment as well as for corrosion and deficiencies at transitions. Roadside barriers on established roads should be reviewed before repairs to the road are made. This inspection is to determine if the barriers are still necessary or if they can be removed because the slope and clear zone are acceptable or can be modified to become acceptable. Unnecessary barriers like these should be removed since barriers themselves are a roadside hazard. The clear zone is an effective life saver. Highway personnel have the responsibility to identify and safely treat any hazardous feature that exists within the right of way. The safety treatment includes removal of natural and man-made hazards whenever possible, proper installation and maintenance of safety devices such as slip bases and crash cushions, appropriate shielding of hazards which cannot be removed or made to safely break away, and routine inspections with documentation of work performed or required. The clear zone begins as a design concept. Only through proper routine maintenance does it remain a life-saving reality. From this tape, how important the clear zone is, we'll take a further look at the clear zone concept. We'll learn how this concept originated and we'll see how the concept evolved to the methods we use today to determine the proper clear zone width for various conditions. General Motors Corporation first found at its test track that about eighty-five percent of vehicles safely recovered within thirty feet of the roadway in run-off-the-road incidents. A clear zone of thirty feet was first adopted as a guideline in the 1967 Yellow Book. This thirty-foot clear zone was still in effect with this 1974 edition of the Yellow Book. The thirty-foot criterion was a beginning, but thirty feet is not always appropriate. In some cases, drivers didn't need thirty feet to regain control of their vehicles. In other cases, they needed much more than thirty feet. What was required was a national criteria for determining a clear zone width appropriate for different situations. In 1977, the Ash Toe Guide for Selecting, Locating, and Designing Traffic Barriers provided the first national criteria based on geometric and operating conditions. This guide also defined the clear zone. That original guide has been replaced by the Ash Toe Roadside Design Guide, which was published in 1989. The clear zone is the area bordering the road, starting at the edge of the traveled way, which is available for use by errant vehicles. Now, four factors contribute to determining the necessary width of the clear zone. One, operating speed. Two, side slope steepness. Three, horizontal curvature. And four, traffic volume. To understand the best contour for the clear zone, we'll look at this film on side slope and ditch tests. This series of tests was conducted to determine how steep a slope a car could go down safely without rolling over. The tests were run on a 20-year-old state highway, with a three and a half to one side slope. A grid pattern was mowed on the surface and striped with chalk to identify the path of the car. The test vehicle is driven by the driver in the trailing truck using a joystick driving system. The car exits at a 25-degree angle, 60 miles per hour. It travels a distance of 168 feet from the edge of the pavement. When the right front wheel slaps down on the front slope, the tie rod is lost and the driver loses control. However, the ride is a safe one with no rollover. In this test, the car exits at 60 miles per hour with a 15-degree angle. The car runs to the bottom with no tendency to be unstable on the side slope. This time, the vehicle went about 185 feet from the edge of the pavement. This test was run at 60 miles per hour with a 10-degree angle to see if the vehicle can be redirected. Counter steering begins one second after the car leaves the roadway. The driver loses control, and as a result, the vehicle travels about 160 feet from the edge of the pavement. The required clear zones under these conditions would be about 100 feet. Obviously, the clear zone will not provide protection for all crash situations. Computer simulations and these tests show that a three-to-one to four-to-one slope is safe. But the vehicle will go to the bottom of the slope. So the clear zone must be adjusted to include the entire slope. At a grade steeper than three-to-one, barriers may be warranted. On a four-to-one slope, the vehicle can be redirected. Operating speed and side slope steepness are used to determine the appropriate clear zone width. For example, a three-to-one slope is very marginal for small vehicles, especially with an unrounded shoulder. Table 3.1 of the Roadside Design Guide will give ranges for specific site conditions. You can see that steepening side slopes and increasing speeds require an increase in the clear zone width. For a flat side slope such as six-to-one and ADT of 5,000, the clear zone is 30 feet at 60 miles per hour. When the fill slope is increased to four-to-one, the clear zone must increase to 32 to 40 feet. Clear zone width is also affected by horizontal curves and the design speed. The basic clear zone width taken from Table 3.1 should be increased by the appropriate factor from Table 3.2 to account for the degree of curvature and the design speed of the roadway in question. The effectiveness of the clear zone depends on more than width. For a clear zone to do its job in providing drivers with a safety margin, it must maintain a continual, clear, flat area. As you'll see, this is not always possible. And when it isn't, other accommodations can sometimes be made. To ensure the safety of the clear zone, all hazards, if at all possible, should be eliminated, either by total removal or by relocation. However, occasionally, objects must remain within the required clear zone. Then the objects must be made as safe as possible or shielded by using breakaway devices to make the object crash-worthy or by using a crash cushion or by placing a longitudinal barrier to prevent errant vehicles from reaching the object. These objects can become hazards in the clear zone. However, by being constantly aware of the importance of maintaining the clear zone, highway engineers can control the location and safety treatment of the objects and thus reduce their impact. Obviously, clear zones are also affected by the terrain. Flat terrains provide the best sites for clear zones, but even flat terrains can be encroached upon, as this railroad crossing proves. As a matter of fact, many situations are beyond the control of highway jurisdiction. Restricted rights of way, trees, and other landmarks which have emotional significance to residents, mailboxes, access points, private driveways, drainage features, and buildings such as in this photo can all interfere with maintaining a clear zone. But even when the clear zone cannot be maintained, drivers can still be provided with a margin for safety. Motorists can adjust their driving to take into account more restricted clear zone conditions if they know where to expect hazards. A consistently designed roadway helps drivers to be aware of obvious hazards. In this case, the hazard is within three feet of the roadway and drivers cannot be forewarned. Throughout our future sessions, we'll discuss identifying and removing potential hazards, such as this tree. When trees are removed, they must be taken down all the way to ground level. Otherwise, a clear roadside can be blemished by a stump, as you see here. The AASHTO Green Book recommends a minimum clear zone of 10 feet on low volume roads. Here we see an excellent example of consistency in a clear zone, even though it may not be the full required width. A clear roadside requires continual maintenance. One, all trees should be removed if possible. Two, ditches should be reshaped for safe traversal, as well as for proper drainage. Three, drainage inlets, breakaway devices, and guardrails must be kept operational. Four, vegetation should be kept under control so a hazard doesn't grow, and bottoms of slopes should be kept free of potential hazards. And finally, five, equipment and materials should be placed so that they are not a hazard. We have discussed the importance of establishing and maintaining an adequate clear zone. You've seen that to ensure maintenance of the clear zone, and consequently, the safety of motorists. Hazards in the clear zone should be removed. Unnecessary hardware should also be removed. Relocated by moving signs, flattening slopes, and extending pipes. Retrofitted with breakaway devices. Shielded with barriers or crash cushions. The three Rs. Remove, relocate, retrofit, and shield. The clear zone concept is essential, and we'll discuss it again in connection with other safety features. For now though, this is the end of our session together. I'll be back to continue our discussion of safe highways.