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17Â Â This chapter focuses on the effects, both positive and negative, of isolated rural intersection lighting. Assessing these effects can be difficult because, by definition, these locations are all different, spread far apart, and unique in many ways (Isebrands etÂ al. 2006). Further, most rural intersections are not lighted (Preston and Schoenecker 1999; Bullough etÂ al. 2013). Nonetheless, crashes at rural intersections constitute a large segment of all fatal crashesâ16% of all traffic fatalities in the United States occur near rural intersections, and the percentage occurring near rural intersections increases to 30% when nighttime fatal crashes are considered (Edwards 2015). A substantial proportion of counties, for example, do not maintain any rural intersection lighting at all (Edwards 2015) and it is important to understand if and how the lighting in these situa- tions can yield benefits. Benefits of Isolated Rural Intersection Lighting on Safety Lighting at isolated rural intersections is not installed for its own sake, but to improve safety at these locations (Martin 2010). Despite the aforementioned challenges to studying whether and how much lighting can reduce nighttime crashes, the safety effects of isolated rural intersection lighting have been a topic of investigation for some time. Preston and Schoenecker (1999) inves- tigated rural intersection lighting in the state of Minnesota and based on their before-and-after investigation, found rural intersection lighting to reduce crash frequency by 25% to 40% and crash severity by 8% to 26%. Based on these results and an average benefit/cost ratio greater than 15:1, Preston and Schoenecker (1999) encourage more agencies to install lighting as a crash counter- measure in rural locations. The ability to quantify and predict the safety benefits of isolated rural intersection lighting is critical to its more effective application (Wortman etÂ al. 1972). C H A P T E R 4 Impacts Chapter Summary â¢ In general, the published literature on the effects of rural isolated intersection lighting suggests that this technique has quantifiable safety benefits, but these benefits may be limited to specific crash types, especially those involving pedestrians. â¢ State transportation agencies rely on crash reports and informal comments from local municipalities and the public to determine how effective lighting is. â¢ Concerns about light pollution have been manifested by the use of lighting systems that (1) do not distribute light in the upward direction and (2) lower CCTs.
18 Lighting Practices for Isolated Rural Intersections The safety findings above were consistent with those from Edwards (2015) who investigated the influence of lighting parameters, specifically the illuminance on the road, as it affects traffic safety, also for rural intersections in Minnesota. It was found that each increase in the horizontal roadway illuminance of 1 lux corresponded to a reduction in the nighttime crash rate by 9% to 20%; this suggests that even lighting that does not meet IES (2018) or AASHTO (2018) recom- mendations could still be beneficial for safety, which was also found by Marks (1977) in his evaluation of reduced rural intersection lighting. Torbic etÂ al. (2015) also found reductions in nighttime crashes, by 70%, when lighting was present at rural intersections, and Transport Canada (2006) stated that lighting in these locations was associated with a 40% reduction at night. Anec- dotal reports of crashes at intersections without lighting have also been published (Morelli 2015; Williams 2015; Hunter 2019). Smaller reductions in nighttime crashes associated with rural intersection lighting have also been reported when other safety-related factors were controlled statistically: 12% by Zhao etÂ al. (2016) and 1.5% by Bullough and Rea (2011). In addition, some studies have found that rural intersection lighting had little measurable effect on nighttime crashes (Rea etÂ al. 2009; Gates etÂ al. 2018). In one study it was suggested that continuous lighting would be more effective than isolated lighting of intersections in rural areas in terms of safety benefits (Stanley Consultants 2013). Part of the reason for these apparently contradictory findings may be the different types of crashes that rural intersection lighting may be able to help reduce. For example, rural inter- section lighting is stated to be effective for crashes involving pedestrians and cyclists (ITE 2014; Thomas and Kemker 2019), for locations with unique alignment (Vogt 1999), and locations with high crash frequencies associated with running stop signs (Preston etÂ al. 2007) or simply high crash rates in general (Oregon DOT 2012). There are also likely differences in the number of luminaires used at each location and the specified light levels; these differences could also account for varied findings in the literature. When asked if they keep track of the effects of lighting at isolated rural intersections, 71% of agencies reported that they did not (FigureÂ 14). For the 29% that did, they were asked what outcomes they tracked (FigureÂ 15). The most frequent way that agencies participating in the survey keep track of the outcomes of rural intersection lighting is by evaluating the crash frequency, either at night (75%) or overall (58%) (FigureÂ 15). Few agencies use surrogate measures such as vehicle speed (8%) to track outcomes, but nearly half (42%) of the agencies that do keep track rely on comments from the local municipality or from the driving public where the rural intersection is located. This likely reflects the remote nature of these installations; it would be expensive to monitor all or even some isolated rural intersections to keep track of outcomes. Of the 33% of participants who FigureÂ 14. Responses to âDoes your agency track the outcomes/impacts of isolated rural intersection lighting?â
Impacts 19Â Â selected âotherâ in response to this question, safety outcomes were most frequently mentioned, but the specific outcomes were not defined. Although the frequency and severity of crashes are the primary ways to assess the benefits of lighting for isolated rural intersections, lighting could have other benefits for visibility and comfort that might not translate easily to an immediate safety outcome. For example, Bhagavathula etÂ al. (2018) reported on a field study of intersection lighting and found that illuminating the conflict area where the intersecting roads overlap made objects within that conflict area more visible from a greater distance away. This aspect is also mentioned in guidance about rural intersection lighting from Hawaii DOT (2013). Depending on the geometry of the lighting, potential hazards could be seen in either negative or positive contrast, and careful pole placement is encouraged (Larimer County [CO] 2016). Lighting at rural intersections is also stated to help reduce the negative effects of glare from oncoming vehicles (Wortman etÂ al. 1972; IES 2000) and to help drivers read signs at night (Colorado DOT 2005; New Jersey DOT 2015). Negative Consequences of Isolated Rural Intersection Lighting Aside from the cost of isolated rural intersection lighting (addressed in ChapterÂ 6, Economics), the use of lighting can have negative consequences, as well. One of the effects most prominently discussed in the literature reviewed for this synthesis was light pollution, an issue of growing concern (Poon 2020). It is mentioned by Cai (2015) that because rural intersection locations tend to be dark with low ambient light levels, the introduction of any lighting into that environment can be noticeable and elicit complaints. Cai (2015) recommends that spill light (light falling onto adjacent properties where it is not intended to provide illumination) be minimized to no more than 3 lux on nearby properties. Civil (2007) has reported complaints by people living close to rural intersections about the light shining into their windows or onto their property. The survey responses for this synthesis indicate that state transportation agencies are largely aware of a trade-off between the potential benefits of lighting and effects such as light pollution and that they have taken some action to control them. For example, dark-sky or light pollution-related criteria were mentioned as being used by 60% of those participating in the survey (FigureÂ 8). When asked to describe the luminaire configurations used for rural intersection lighting (FigureÂ 11), 65% of those respondents reported using cutoff luminaires, luminaires with restricted BUG ratings FigureÂ 15. Responses to âWhich outcomes/impacts of isolated rural intersection lighting does your agency track?â
20 Lighting Practices for Isolated Rural Intersections (IES 2011), or systems that produce no upward light (some reported using more than one of these configurations). One agency mentioned that in response to potential impacts on astronomical observation from the spectral output from outdoor lighting, they have moved to lower CCTs for their lighting systems. As lighting systems are large fixed objects along the roadway, another potential consequence of installing isolated rural intersection lighting is an increased risk of collisions with lighting poles. As mentioned previously, locating poles a minimum distance from the road, such as 12Â feet (Wisconsin DOT 2005) or mounting lighting to other structures that might be present such as signal masts (New Hampshire DOT 2010) can help to mitigate this risk.