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54 Many safety devices have been developed, and a few have been pilot-tested and evaluated with good results. Although STAs or LPAs have used some of these safety devices on a case-by-case basis, this synthesis report has not identified any UOs that have adopted these devices for routine use to safeguard the public from crashes with hazardously located utility poles. Safety devices that would be suitable for shielding vehicles from utility poles are discussed in the Roadside Design Guide (AASHTO 2011b), which is widely used by STAs and constitutes an equally valuable guide for UOs. However, UOs have rarely chosen to install such safety devices, instead tending to rely on guides such as the National Electrical Safety Code (Institute of Electrical and Electronic Engineers 2017), which does not consider the safety of the highway traveling public. For years, STAs have proved that structures such as crash cushions, guardrails, concrete barriers, and breakaway or yielding devices are effective in protecting the public from rigid obstacles in rights-of-way; yet, most UOs have overlooked these same proven devices, even when so-called high-risk poles are obvious. A cursory inspection of the Roadside Design Guide (AASHTO 2011b) uncovers at least 14 crash cushions, 14 guardrail and end treatments, 2 concrete barriers, and 1 breakaway structure that can be applied to the treatment of identified high-risk poles. While some of these safety devices were originally tested under the requirements of NCHRP 230 (Michie 1981) or NCHRP 350 (Ross et al. 1993), those documents have now been replaced by the Manual for Assessing Safety Hardware (MASH) (AASHTO 2016b). Since the acceptance of that manual and the revision of 2016, most of the guardrail end treatments (e.g., SoftStop, SKT, SLED, and MAX) have met the new MASH (AASHTO 2016b) requirements. Many crash cushions (e.g., QuadGuard, CrashGuard, and Big Sandy) have also been approved under MASH (AASHTO 2016b) requirements. Guidry and Beason (1992) developed the low-profile concrete barrier, which was tested under NCHRP 350 (Ross et al. 1993) Test Level (TL) 2. Under TL 3, Dobrovolny, Shi, and Bligh (2018) qualified a new design of the low-profile barrier under MASH TL-3 conditions. The steel-reinforced safety pole (i.e., Hawkins, FHWA, or AD-IV) was originally tested and qualified under NCHRP 230 (Michie 1981) by Ivey and Morgan (1986) and by Alberson and Ivey (1994). These designs have not been retested under NCHRP 350 (Ross et al. 1993) or MASH (AASHTO 2016). More than 30 safety devices were applicable, according to the Roadside Design Guide (AASHTO 2011b), and many more designs have been approved under MASH (AASHTO 2016b). The following relatively low-cost items were cited in the Roadside Design Guide (AASHTO 2011b): â¢ Crash cushion (sand inertia barrels) (page 8â38) â¢ Guardrail/end treatment (W section extruder) (page 8â13) C H A P T E R 8 Safety Devices
Safety Devices 55 â¢ Portable concrete barrier (conventional 32-inch and low-profile 20-inch) (pages 9â8, 9â23) â¢ Breakaway structure (steel-reinforced safety shape) (page 4â35). Ivey and Scott (2000) have suggested that safety structures (cushions, rails, or yielding or breakaway devices) in Texas should be required when a UO requests an exception to the STA clear zone policy. If the state chooses to provide the safety structure, the UO would bear the cost of installation and maintenance as long as it chooses to locate poles within the STA clear zone (Ivey and Scott 2000). Examples of these safety devices are discussed in the rest of this chapter. Crash Cushions Crash cushions ranging from simple and effective sand-filled barrels to the most sophisticated devices (e.g., CrashGuard) are appropriate to shield vehicle occupants from hazardously located utility poles. At least seven approved designs are listed in the 4th edition of the Roadside Design Guide (AASHTO 2011b). Various crash cushion designs were first installed as early as 1977 (AASHTO 1977). The most cost-effective crash cushions yet developed are sand-filled barrels, implemented where continual collision recurrences are not expected. Figure 22 shows an instal- lation in Lafayette, LA, with a pole situated in a high-risk location near traffic on a curve where chevrons were also used to better delineate the curve. Composite Utility Poles Foedinger et al. (2003) developed a fiberglass-reinforced composite utility pole designed to absorb vehicle kinetic energy during a collision (Figure 23). The Shakespeare composite utility pole is constructed of filament-wound fiberglass-reinforced polyester that is tapered (from bottom to top) along its 45-foot length. The cross-section is octagonal and hollow at the base and transi- tions to a hollow circular cross-section near the top of the pole. Some of the advantages of the Figure 22. Examples of installations of sand barrel crash cushions (Photos: Don Ivey).
56 Utility Pole Safety and Hazard Evaluation Approaches fiberglass-reinforced pole over traditional wooden poles include weight savings (475 pounds compared to 1,000 pounds), increased service life (80 years of uniform performance compared to 20 to 50 years of declining performance), and reduced maintenance and faster installation. In demonstration projects, this pole has replaced some atypically exposed wood poles in New Jersey, but no collisions have been recorded. Gabler, Gabauer, and Riddell (2007) conducted a comprehensive study of energy-absorbing utility poles and steel-reinforced safety poles that was performed for the New Jersey DOT. They found various situations where both energy-absorbing poles and steel-reinforced safety poles were cost-effective, further reinforcing many of the conclusions and approaches to alleviate the human cost of poles in high-risk locations that TRB State of the Art Report 9 (Ivey and Scott 2004) presented. Steel-Reinforced Safety Poles FHWA sponsored research in the early 1980s to develop an economical âyieldingâ timber utility pole that would increase the safety of passengers in impacting vehicles and would satisfy the design criteria of the utility industry. Consequently, Ivey and Morgan (1986) developed a slip-base design referred to as the Hawkins Breakaway System (HBS). This design consisted of a slip-base mechanism 3 inches above grade and an upper hinge consisting of a band and strap mechanism that allowed the bottom pole segment to rotate in response to a colliding vehicle. Subsequently, the Massachusetts Electric Cooperative and the New England Telephone Company installed 19 experimental HBS poles near Boston. Examples of steel-reinforced safety poles are shown in Figure 24. The HBS was subsequently improved during field tests in Massachusetts that showed the pole was stronger during wind loads than the new Class 4 wood poles. Buser and Buser (1992) called this modified design the FHWA design. FHWA provided technology application funds in 1989 for experimental installations of the design in Kentucky, where the Kentucky Utilities Company Figure 23. Example of a composite breakaway utility pole (Foedinger et al. 2003).
Safety Devices 57 retrofitted 10 existing wooden poles in Lexington, and again in 1995 in Virginia, where Delmarva Power installed five poles on the Eastern Shore. Alberson and Ivey (1994) introduced an improved version of the HBS, known as the AD-IV. Improvements to the previous system included switching from a six-bolt circular lower slip-base connection to a four-bolt square slip-base connection and converting the upper connection from a four-strap shearing mechanism to a four-strap/four-bolt design. These changes reduced the amount of material used in the base connection, lowered the cost of the upper hinge, and decreased the maintenance costs. FHWA furnished technology application funds in 1994 for experimental installations of the AD-IV design in Texas, where the Texas Electric Company installed six poles on an urban arterial road between Fort Worth and Dallas. FHWA required evaluation of all the experimental poles for several years after installation, with the results noted below (Buser and Buser 1992). Massachusetts evaluated the HBS FHWA design 2 years after installation. During that time, although all poles were exposed to wind, ice, and snow, no pole exhibited failures because of these natural forces. An incident in Massachusetts in 1991 (during Hurricane Bob) displayed the ability of the poles to resist wind loadings that toppled conventional poles. Poles in Massachusetts were hit by errant vehicles five times during the evaluation period, resulting in no serious injuries or deaths, no loss of utility service, no safety problems relative to linemen, and an average repair time of 90 minutes. In all these crashes, utility personnel indicated that the poles could be repaired quicker and more easily than standard poles, primarily because the need to transfer service lines was eliminated. Since the time of the evaluation, it was later reported by Horne (2001) that the poles were observed periodically and that some of them (for unknown reasons) were replaced with conventional poles; however, those that remained were in excellent condition, including both the galvanized steel elements and the wooden pole segments. Texas evaluated the AD-IV 3 years after installation and reported only one crash (in 1995). This crash involved the one pole in the group that was improperly installed on a 2:1 slope approximately 10 feet from the paved shoulder. The bottom of the slip base was too high, almost 12 inches Figure 24. Examples of steel-reinforced safety poles (Photos: Don Ivey).
58 Utility Pole Safety and Hazard Evaluation Approaches above the ground line at the part of the base farthest from the traveled lane. An effort was made to regrade the slope to the proper level, but heavy rains immediately before the crash eroded the newly placed soil. Despite that, the pole functioned during the collision, and no serious injuries occurred. The car frame snagged on the lower plate of the slip base, clearly increasing the deceleration of the vehicle, and the delay in slip-base activation fractured the middle length of the pole and tilted part of the pole in the ground. As a result, the pole was completely replaced. In the 3 years the AD-IV poles were in place at the time of the evaluation, the poles weathered several instances of high winds, including a hailstorm that destroyed the roof and west wall of virtually every building that was not sheltered by trees or other buildings. Texas Electric Company engineers noted that some wind gusts were as high as 80 mph and that some conventional poles were downed. The AD-IVs sustained no damage during these weather events. Kentucky evaluated the modified HBS FHWA design 2 years after installation, reporting that the poles performed well in high winds (up to 80 mph) and that maintenance costs included only those expenses necessary to straighten the upper segments of the poles. Such maintenance was unnecessary thereafter because wood shrinkage became minimal after 1 to 2 years of exposure. The poles were not located in areas known for crashes; thus, as expected, none of the poles was hit during the evaluation period. Virginia evaluated the modified HBS FHWA design 2 years after installation and reported no maintenance costs or problems, despite several instances of high winds. No reports were filed citing pole damage or even modest deformation. Low-Profile Barrier The low-profile barrier is simply a short portable concrete barrier (20 inches tall). It has been used extensively in construction zones in Texas. In short lengths, low-profile barriers can be placed to prevent vehicle entry into an area where a utility pole stands in the needed clear zone. The low-profile barrier is qualified now under MASH TL-2. In Des Moines, IA, a low-profile barrier was erected in the median to shield drivers from trees as well as from light poles and fixed aesthetic features. The barrier terminates with a sloped-down end section where the median narrows adjacent to left-turn lanes. At a height of only 20 inches, the barrier has a minimal visual impact. As a mitigation tech- nique, the barrier is expected to reduce crash severities. During a design process that incorporates such a feature, it is important to consider that the installation of the low-profile barrier may also affect pedestrian movements, potentially discouraging crossings at unmarked mid-block locations. Guardrails and Various Terminals Short sections of guardrail are sometimes used to shield hazardously located utility poles, as illustrated in Figure 25. Breakaway Guy Wires FHWA developed and approved several breakaway guy wire systems for use on the National Highway System. The starting point for breakaway guy wire designs was provided by an opera- tional breakaway guy wire connection that was developed and successfully tested in 1986 under an FHWA-sponsored research project, NCHRP 230 TL-3. Details of the design are presented in the FHWA report, Safer Timber Utility Poles (Ivey and Morgan 1985). The breakaway guy attachment is intended for use where the anchor guy will be exposed to vehicular traffic, particularly when the anchor guy extends toward traffic. If no records are available on the number of collisions that involve utility anchor guys within road and street rights-of-way, such collisions probably still do occur, resulting in injuries and deaths. An illustration of a breakaway guy cable is shown in Figure 26.
Safety Devices 59 Delineation FHWA and the Maryland State Highway Administration initiated a pilot study in 1999 to delineate utility poles and other fabricated fixed objects within the highway right-of-way. The study was designed to cost-effectively enhance roadside safety when removal, relocation, and shielding of manufactured fixed objects were not feasible. Recognizing that about 5% of Marylandâs highway-related fatalities resulted from collisions with utility poles, FHWA and the Maryland State Highway Administration met with representatives from Allegheny Power, Bell Atlantic, Pepco, and BT&E to coordinate the delineation of a sampling of poles. Pilot roadway sections totaling 70 miles were selected based on crash data and geometrics. All fabricated fixed objects within the pilot roadway sections were delineated with a 6-inch yellow reflective sheeting material (Figure 27). It is considered probable that delineation had a positive effect, but follow- up studies were not sufficiently comprehensive to confirm that effect. Figure 25. Example of guardrail and extruder terminal (Photo: Don Ivey). Figure 26. Example of a breakaway guy wire (Source: Delaware DOT).
60 Utility Pole Safety and Hazard Evaluation Approaches Buried Duct Network of Cables Slavin and Najafi (2010) developed the buried duct network for FHWA to accommodate utility cables along roads and highways. It represents a departure from conventional direct bury construction methods for utility lines (electric power, telephone, and cable television), which lays cables in a trench along the local distribution route. The buried duct network offers an opportunity for conveniently and safely completing cable upgrades at a low incremental cost to the utilities and their customers by using a joint-use upgradable system. Such a system is designed to encourage and support the installation of belowground utilities, thereby minimizing construction difficulties and hazards, including the proliferation of pole lines. In this research, a set of two full-scale field trials was planned and executed at the University of Texas at Arlington: one in Monroe, NC, and one in Massachusetts (Figure 28). Figure 27. Examples of reflective tape on utility pole (left) and reflective panel (right) (Photos: Kevin Zegeer). Note: For thoroughfare application, possibly omit service lines Utility terminals/equipment/hardware (power, telephony, CATV) Handhole Three individual service ducts Common (joint) service trench Common (joint) main trench along ROW Two vacant large ducts through handhole Initial primary power distribution cables (direct-buried, w/o duct) Initial distribution cables (direct-buried, w/o duct) Figure 28. Diagram of buried duct network of utility cables.