# Utility Pole Safety and Hazard Evaluation Approaches(2020)

## Chapter: Chapter 4 - Factors Associated with Utility Pole Crashes

« Previous: Chapter 3 - Summary of STA Survey Responses
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Suggested Citation:"Chapter 4 - Factors Associated with Utility Pole Crashes." National Academies of Sciences, Engineering, and Medicine. 2020. Utility Pole Safety and Hazard Evaluation Approaches. Washington, DC: The National Academies Press. doi: 10.17226/25923.
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Suggested Citation:"Chapter 4 - Factors Associated with Utility Pole Crashes." National Academies of Sciences, Engineering, and Medicine. 2020. Utility Pole Safety and Hazard Evaluation Approaches. Washington, DC: The National Academies Press. doi: 10.17226/25923.
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Page 27
Suggested Citation:"Chapter 4 - Factors Associated with Utility Pole Crashes." National Academies of Sciences, Engineering, and Medicine. 2020. Utility Pole Safety and Hazard Evaluation Approaches. Washington, DC: The National Academies Press. doi: 10.17226/25923.
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Page 28
Suggested Citation:"Chapter 4 - Factors Associated with Utility Pole Crashes." National Academies of Sciences, Engineering, and Medicine. 2020. Utility Pole Safety and Hazard Evaluation Approaches. Washington, DC: The National Academies Press. doi: 10.17226/25923.
×
Page 29
Suggested Citation:"Chapter 4 - Factors Associated with Utility Pole Crashes." National Academies of Sciences, Engineering, and Medicine. 2020. Utility Pole Safety and Hazard Evaluation Approaches. Washington, DC: The National Academies Press. doi: 10.17226/25923.
×
Page 30
Suggested Citation:"Chapter 4 - Factors Associated with Utility Pole Crashes." National Academies of Sciences, Engineering, and Medicine. 2020. Utility Pole Safety and Hazard Evaluation Approaches. Washington, DC: The National Academies Press. doi: 10.17226/25923.
×
Page 31
Suggested Citation:"Chapter 4 - Factors Associated with Utility Pole Crashes." National Academies of Sciences, Engineering, and Medicine. 2020. Utility Pole Safety and Hazard Evaluation Approaches. Washington, DC: The National Academies Press. doi: 10.17226/25923.
×
Page 32
Suggested Citation:"Chapter 4 - Factors Associated with Utility Pole Crashes." National Academies of Sciences, Engineering, and Medicine. 2020. Utility Pole Safety and Hazard Evaluation Approaches. Washington, DC: The National Academies Press. doi: 10.17226/25923.
×
Page 33
Suggested Citation:"Chapter 4 - Factors Associated with Utility Pole Crashes." National Academies of Sciences, Engineering, and Medicine. 2020. Utility Pole Safety and Hazard Evaluation Approaches. Washington, DC: The National Academies Press. doi: 10.17226/25923.
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26 Utility Pole Safety and Hazard Evaluation Approaches or pole spacing) was the most important variable in predicting the probability of utility pole crashes. Lateral pole offset from the road represented the next most important feature, followed by road grade, road path (curvature), and speed limit. Mak and Mason (1980) conducted a detailed study of crashes that involved utility poles, sign poles, and light poles in seven geographic areas in the United States. Pole crashes were found to be primarily an urban problem, with 85% of such crashes occurring in urban areas. The overall crash rate in terms of pole crashes per 100 million vehicle miles was 16 (i.e., 9.9 crashes per hundred million vehicle kilometers). Mak and Mason also concluded that the frequency of pole crashes was most highly associated with pole density, pole offset, and horizontal and vertical alignment. Factors Related to Pole Crash Severity Several researchers studied the effects of traffic and roadway variables on the severity of utility pole crashes. Fox, Good, and Joubert (1979) found crashes on horizontal curves to be slightly more severe than those on tangent sections because of the increased number of side impacts on curves. Utility pole crashes were more severe at nonintersections than at intersections, probably the result of lower vehicle speeds at intersections. The Jones and Baum (1980) study indicated that 49.7% of all utility pole crashes caused personal injuries. They observed that impact speeds and pole circumference were related to the severity of utility pole crashes, but the spacing and offset of utility poles did not affect utility pole crash severity. Mak and Mason (1980) reported a 50% chance that at least one vehicle occupant will be injured in a utility pole crash, closely matching the Jones and Baum study results. Of the 1,000 utility pole crashes included in the study, 518 (51.8%) involved one or more injuries, and 16 (1.6%) resulted in one or more fatalities. Vehicle impact speed ranked as a major factor in crash severity; other factors included utility pole type (e.g., wood, metal), presence of yielding poles, vehicle characteristics (e.g., weight, size), and impact configuration (collision location and direction of impact). Griffin (1981) studied single-vehicle crashes in Texas, finding that 44.7% of utility pole crashes involved a personal injury. Furthermore, about 33.5% of such crashes resulted in a moderate injury (B-type injury) or worse, and 5.8% involved a serious injury (A-type injury) or a fatality. In their study of clear zones, Graham and Harwood (1982) uncovered no relationship between an agencyâs clear zone policy (i.e., 6:1 clear zone, 4:1 clear zone, no clear zone) and the severity of fixed-object crashes. Safety Appurtenances Several previous studies addressed the issue of the effectiveness of various crash-related counter- measures, such as placing utility lines underground (and removing the poles), increasing the lateral offset of poles, installing protective barriers (e.g., guardrails), reducing the number of poles, using yielding (breakaway) poles, and employing other options. Each countermeasure is discussed below. Most of the previous studies confirmed that burying utility lines reduces the overall severity of fixed-object crashes, based on the assumption that other less-rigid objects will be hit instead of the utility pole. The net effect is highly dependent on site-specific roadside characteristics, such as roadside slope and the number and type of other obstacles (e.g., trees, mailboxes, and other rigid objects). Some of the challenges encountered in running utility lines underground include

30 Utility Pole Safety and Hazard Evaluation Approaches To illustrate the results of applying the predictive model to a countermeasure such as pole relocation, consider the values of the crash-reduction factors shown in Table 4. The first column lists the utility pole distance in the current situation; the proposed new pole offset distances are shown at the top of each of the remaining columns. To use the chart, find the current offset (first column), and move to the right along the row to locate the proposed offset column. The cell at that intersection notes the expected percent reduction in crashes. For example, if a pole is currently 5 feet from the road, moving it to 10 feet should result in approximately a 56% reduction in crashes. By using the nomograph with various ADT, pole offset, and pole density values, the sensitivity of the model to such factors is easily seen. In the previous example, changing the pole offset from 5 feet to 15 feet, for instance, would reduce the number of crashes from about 1.15 down to 0.55, approximately a 50% reduction in predicted pole crashes. The safety effects of changing combinations of pole offset and pole density can be seen as well. This crash-prediction model was used in the Zegeer and Parker (1983) study to compute the expected crash reductions for various countermeasures related to relocating poles and/or reducing the number of poles exposed to motorists within a roadway section. A series of tables was generated for this report on ARFs for pole relocation and pole density reduction, as given in the utility pole userâs manual by Zegeer and Cynecki (1986). For example, Table 5 in this synthesis report shows the expected ARFs for reducing pole density at a site with an ADT of 25,000 vehicles. Table 5 shows separate calculations for different pole offsets (3, 7, 15, and 25 feet from the road), using different pole densities before and after improvement (10 to 70 poles per mile, in increments of 10 poles per mile). Similarly, Table 6 corresponds to the expected ARFs for increasing pole offset from the roadway edge-line for an ADT of 25,000 vehicles. Table 6 gives separate calculations for densities of 20, 40, and 75 poles per mile, using poll offsets of 2 to 15 feet from the road before improvements and 6 to 30 feet after improvements. The full userâs manual (Zegeer and Cynecki 1986) includes more tables than this synthesis report. Figure 11. Utility pole crash-prediction nomograph (Zegeer and Parker 1983).

Factors Associated with Utility Pole Crashes 31 Table 4. Accident (crash) reduction factors (Zegeer and Parker 1983). Table 5. Accident (crash) reduction factors associated with reducing pole density (Zegeer and Cynecki 1984).

32 Utility Pole Safety and Hazard Evaluation Approaches Table 6. Accident (crash) reduction factors associated with increasing lateral pole offsets (Zegeer and Cynecki 1984). The Zegeer and Parker (1983) study also identified the following several factors associated with the likelihood of serious injuries and deaths for the 9,583 utility pole crashes in the research database: â¢ Pole type. For roadway sections where pole offsets from the road were 10 feet or less, wooden poles (compared to metal poles) were associated with a significantly greater severity of inju- ries and deaths. This outcome is likely because many of the metal poles in the database were luminaire poles with frangible bases that break away when struck. â¢ Horizontal curvature. Utility poles on roadway sections with increasing curvature experi- enced more severe utility pole crashes (when compared to tangent sections) for certain speed limit categories (i.e., speed limits under 35 mph and over 50 mph). â¢ Speed limit. No significant effect was documented between roadway speed limit and crash severity. This outcome possibly resulted from fewer categories of injury severity (PDO, injury, and fatality) compared to previous studies, such as that of Jones and Baum (1980), which analyzed more detailed data on crash severity.

Factors Associated with Utility Pole Crashes 33 In summary, crash frequency was clearly related to ADT, pole offset, and pole density, with lesser factors including type and size of pole, roadway curvature, and roadway type (divided or undivided). Crash severity was most related to pole type and roadway curvature. Table 7 summarizes the relationships between (1) utility pole crash frequency and severity and (2) various roadway features, based on a literature review by Zegeer and Parker (1983). Table 7. Summary of relationships between utility pole crash frequency and severity versus roadway factors (Zegeer and Parker 1983).

Next: Chapter 5 - Identification of Utility Poles in High-Risk Locations »
Utility Pole Safety and Hazard Evaluation Approaches Get This Book
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In 2017, the latest year for which data are available, 887 fatal utility pole crashes occurred in the United States, accounting for 914 fatalities. These numbers were about the same as those in recent years but lower than such fatality numbers from a decade or two ago.

The TRB National Cooperative Highway Research Program's NCHRP Synthesis 557: Utility Pole Safety and Hazard Evaluation Approaches summarizes the strategies, policies, and technologies that state transportation agencies (STAs) and utility owners (UOs) employ to address utility pole safety concerns.

Specific areas of interest for this synthesis report include methods to identify problem poles and high-risk locations, pole-placement policies, strategies and countermeasures to reduce the risk of pole-related collisions and resulting injuries and deaths, and available funding sources for implementing countermeasures. Case studies were also developed for exemplary STAs and UOs, highlighting some of their utility pole safety activities.

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