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12 Table 5. Severity of NYSDOT work zone rear-end crashes. Injury Severity All Work Zone Traffic Lane Closure Traffic Control Control Types Work Zones Only Daytime Nighttime Daytime Nighttime Work Work Work Work Operations, Operations, Operations, Operations, Daytime Nighttime Daytime Nighttime Crashes Crashes Crashes Crashes (n = 863) (n = 112) (n = 524) (n = 83) Fatal 0.3% 2.7% 0.6% 2.4% Injuries 35.2% 42.9% 31.1% 34.9% PDO 61.9% 54.4% 68.5% 62.7% Chi-Square Test Results Daytime and nighttime Daytime and nighttime distributions are not distributions are not significantly differenta significantly differentb a X2 = 3.307 < X 2 Crit (1, 0.025) = 5.024 b X2 = 1.622 < X 2 Crit (1, 0.025) = 5.024 is not possible to determine from the analysis whether the ac- of fatalities and injuries associated with intrusion crashes is tual risk of such crashes increases at night, or whether the greater at night than during the day. However, whereas the dif- shift in the relative frequencies between daytime and night- ference in percentages between nighttime and daytime is sta- time work conditions is instead the result of a lower relative tistically significant for all work zone types combined, it is not frequency of rear-end crashes associated with nighttime op- when only lane closure intrusion crashes are considered. erations. Still, the fact that intrusion crashes involving work- ers are a greater proportion of nighttime work zone traffic crashes in general may partially explain why the highway Work Zone Construction worker perceives night work to be more hazardous. Accident Analysis Although night work is associated with a lower percentage Types of Construction Worker Accidents of rear-end crashes relative to daytime work activities, the question still exists as to whether the rear-end crashes that do Table 7 presents the relative frequency of different types of occur at night are more severe because of generally higher construction worker accidents reported at NYSDOT work traffic speeds. The comparison of day and night operations in zones on freeway and expressway facilities during daytime Table 5 indicates that a slightly greater percentage of rear-end and nighttime work activities. Overall, the percentages are crashes in night work operations involves fatalities and in- similar between daytime and nighttime conditions, with no juries, both for all work zones and for those at lane closures. statistically significant differences detected. Accidents involv- However, the differences are not statistically significant. A sim- ing tools or construction materials are the largest category, ilar comparison of the severity of workspace intrusion crashes followed by strains caused by slipping or tripping and acci- between daytime and nighttime conditions is shown in Table 6. dental contacts with utilities. The percentage of accidents that Similar trends are evident when all work zone types combined involve workers being hit by construction vehicles or equip- are considered, specifically for lane closures. The percentage ment in the work zone is nearly identical for daytime and Table 6. Severity of NYSDOT workspace intrusion crashes. Injury Severity All Work Zone Traffic Lane Closure Traffic Control Control Types Work Zones Only Daytime Nighttime Daytime Nighttime Work Work Work Work Operations, Operations, Operations, Operations, Daytime Nighttime Daytime Nighttime Crashes Crashes Crashes Crashes (n = 133) (n = 39) (n = 86) (n = 26) Fatal 2.3% 7.7% 2.2% 0.0% Injuries 36.8% 53.8% 36.3% 56.4% PDO 60.9% 38.5%a 61.5% 43.6%b Chi-Square Test Results Daytime and nighttime Daytime and nighttime distributions are significantly distributions are not differenta significantly differentb a X2 = 7.419 > X 2 Crit (1, 0.025) = 5.024 b X2 = 2.728 < X 2 Crit (1, 0.025) = 5.024