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Suggested Citation:"Summary." National Academies of Sciences, Engineering, and Medicine. 2021. LED Roadway Lighting: Impact on Driver Sleep Health and Alertness. Washington, DC: The National Academies Press. doi: 10.17226/26097.
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Suggested Citation:"Summary." National Academies of Sciences, Engineering, and Medicine. 2021. LED Roadway Lighting: Impact on Driver Sleep Health and Alertness. Washington, DC: The National Academies Press. doi: 10.17226/26097.
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1   The broad goal of this project was to determine the impact of light-emitting diode (LED) roadway lighting on driver sleep health and alertness (DSHA). Sleep health was evaluated based on melatonin levels in saliva. Driver alertness was measured objectively using driver detection and color recognition distances (reaction times), percentage of time that a driver’s eyelids were closed over a 3-minute segment (percentage eyes closed or PERCLOS), and standard deviation of lateral position (SDLP), as well as subjectively using the Karolinska Sleepiness Scale (KSS). Ten healthy participants, ages 18 to 30 years and with a steady sleep-wake cycle, participated in the study. Each participant encountered one light type and level in each of five experimental sessions, which were separated by a minimum of 1 week. At the start of each experimental session participants were exposed to 200 lux, which is typical of residential lighting, from 11:00 PM to 1:00 AM. The following findings are based on the results of the study: • LED roadway lighting, even at levels higher than those specified in the Illuminating Engineering Society of North America (IES) recommended practice (RP) 8–18, does not significantly suppress salivary melatonin from 1:00 AM to 3:00 AM in healthy drivers. • There are no statistical differences in salivary melatonin suppression between LED and high-pressure sodium (HPS) roadway lighting when measured at the same light level (roadway luminance of 1.5 cd/m2 or a corneal illuminance of 1.9 lux). • There are no statistical differences in salivary melatonin suppression between any LED or HPS roadway lighting condition and a roadway without electrical lighting. • No statistically significant differences in any roadway lighting condition (LED or HPS) or no-roadway-lighting condition were observed for objective measures of driver alertness, as measured by detection and color recognition distances (reaction times), PERCLOS, and SDLP. • An increase in the exposure time of HPS roadway lighting resulted in a statistically sig- nificant decrease in the detection and color recognition distances. Such differences were not observed for LED or no-roadway-lighting conditions. • There were no statistical differences between the HPS, LED, and no-roadway-lighting conditions for subjective driver alertness as measured by KSS. Based on these findings, it can be concluded that at the light levels specified in IES RP-8-18, LED roadway lighting does not affect drivers’ salivary melatonin or alertness from 1:00 AM to 3:00 AM. The results from this study do not support a need to modify the guidelines for LED roadway lighting for affecting human melatonin suppression and alertness. The application of roadway lighting should be considered in terms of several different aspects affecting the road user and the built environment. These include road safety, energy conservation, road user acceptance, road user health, sky glow and light trespass, and impact Summary

2 LED Roadway Lighting: Impact on Driver Sleep Health and Alertness on the surrounding ecology. This project considered primarily the impacts on salivary mela- tonin suppression, roadway safety (using visual performance as a surrogate), and alertness. The results show that the spectral content and intensity of roadway lighting do not affect the salivary melatonin suppression or alertness in human participants. As a result, spectral power distribution (SPD) of the light source is not likely a consideration on the health of roadway users (particularly drivers), as the light dosage in the roadway is too low to elicit a measurable effect. This study had some limitations. Only one aspect of sleep health—salivary melatonin suppression—was measured and only in roadway lighting exposures from 1:00 AM to 3:00 AM. Future studies would benefit from the measurement of plasma melatonin over longer nighttime durations. Importantly, future studies should evaluate other measures of sleep health such as sleep onset, the number of awakenings, sleep duration, sleep efficiency, and quality of sleep, in more realistic environments and for longer periods, to understand better the effect of roadway lighting on sleep health. The literature review conducted as part of this study showed that roadway lighting (LED and HPS) has a detrimental effect on sky glow, light pollution, flora, and fauna (Longcore et al., 2018; Palmer et al., 2018; Palmer et al., 2017). Adequate care should be taken to minimize those effects.

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Light emitting diode (LED) technology has revolutionized the lighting industry. The dimming and instant-on capabilities of these light sources along with their high efficiency have allowed lighting designers to overcome some of the limitations of previous technologies, particularly in roadway lighting environments. However, concerns related to the health and environmental impacts of LEDs have been raised.

The TRB National Cooperative Highway Research Program's NCHRP Research Report 968: LED Roadway Lighting: Impact on Driver Sleep Health and Alertness seeks to determine the impact of LED roadway lighting on driver sleep health and alertness.

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