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4 CHAPTER 1 Background Problem Statement roadways at night than during the day (4, 5, 6). Driver ex- pectancy to encounter roadwork activity may also be less at Most roadwork today involves reconstruction, rehabilita- night than during the day in some areas, depending on how tion, and maintenance of existing roadways and often occurs extensively night work has been embraced by those regions in or near moving traffic. More and more, agencies are doing in recent years and how well the night work is publicized to roadway work on high-volume facilities at night to reduce drivers. Each of these factors may have the potential to increase adverse traffic impacts and complaints by the public that crash risk per vehicle and crash severity at night, compared to typically occur when the same work is done during the day. daytime conditions. Minimizing traffic impacts of roadwork activities is a key The fact that arguments exist on both sides of the question emphasis of the Federal Highway Administration (FHWA) (1). as to whether working at night is more or less safe than work- Nighttime travel is commonly characterized by the ing during the day emphasizes the need for this research. following: Rather than continuing to rely on conjecture and subjective opinion, NCHRP initiated this project to objectively deter- Lower traffic volumes, mine and document how nighttime and daytime work zones A higher percentage of truck traffic, affect traffic safety. Four specific objectives were identified: Higher operating speeds, Reduced visibility, and Determine the crash rates for nighttime and daytime work Higher concentrations of drowsy and impaired drivers. zones; Determine the nature of, and identify similarities and dif- Traffic volumes at night on a roadway facility are typically ferences between, traffic-related crashes in nighttime and much lower than during daylight hours, which is often the daytime work zones; Develop management practices that promote safety and main reason that work is performed at night. Lower traffic volumes yield reduced vehicular exposure to the work zone, mobility in nighttime and daytime work zones; and Develop work zone crash reporting recommendations to which is a key determinant associated with crash frequencies. Furthermore, working during nighttime hours reduces the further improve the data collected on work zone crashes. likelihood and extent of traffic congestion that could result from performing that work. Traffic congestion has been Previous Research associated with higher crash frequencies and rates by several Work Zone Effects on Traffic Safety researchers (2, 3). However, lower volumes provide greater maneuverability Over the past 30 years, numerous researchers have examined to drivers, and can allow higher operating speeds to occur the influence of work zones on roadway crashes, primarily in into and through the work zone than would have been possi- terms of how normal crash rates or the likelihood of crashes ble had the work been done during the day. Obviously, lower changes when a work zone is installed at a particular location. light levels at night reduce visibility for drivers and workers In recent years, one finds that crashes typically increase ap- relative to what would be available during the day. Based on proximately 20 to 30 percent within work zones relative to crash data and other collected information, it is well recog- the normal crash experience for those locations, although the nized that greater concentrations of impaired drivers are on amount of the increases varies from study to study (7, 8, 9, 10,