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65 CHAPTER 6 Findings and Recommendations This research was performed to determine: how nighttime crash risk are higher for the PDO crashes than for injury and and daytime work zones affect crash risk and rates; to deter- fatal crashes, indicating that the additional crashes that occur in mine similarities and differences in the characteristics between work zones tend to be less severe in nature. This trend exists traffic crashes at nighttime and daytime work zones; to iden- regardless of whether the work is performed during the day tify and evaluate various management practices to promote or at night. The only exception to this finding was for intru- safety and mobility in nighttime and daytime work zones; sion crashes extracted from the NYSDOT database. In that and to identify and develop recommendations to improve the particular subset of the data, intrusion crashes during night- data collected, archived, and analyzed regarding work zone time work operations involved a higher percentage of injury traffic crashes. Based on analysis of data from five states (New and fatal crashes than did intrusion crashes during daytime York, California, North Carolina, Ohio, and Washington), work operations. Not all injuries or fatalities in either time the key findings from this research are summarized in the period involved highway workers; many were drivers and section that follows. passengers of the intruding vehicles. Although the increased risk of a crash is similar, differences do exist in the types of crashes that occur at nighttime and daytime Findings work zones. For example, based on the NYSDOT work zone traffic crash and worker accident database, those traffic crashes Nighttime and Daytime Work Zone Effects involving workers, construction vehicles or equipment, and on Crashes and Worker Accidents construction materials and debris (both intrusion and non- Overall, working at night does not result in significantly greater intrusion crashes) comprise a greater percentage of crashes at crash risk for an individual motorist traveling through the work night than during the day. Furthermore, intrusion crashes in- zone than does working during the day. When work activity is volving workers are also a higher percentage of crashes at occurring and travel lanes are temporarily closed, the risk of night than during the day. However, they are only a small a crash for an individual motorist traveling through the work proportion of the total work zone crash experience in either zone increased by about 66 percent during the day and by time period. 61 percent at night, compared to the expected crash risk that Nighttime and daytime work zones also affect rear-end would normally exist at a particular location. The actual traffic crash percentages differently. Although the percent of change in crash risk varied substantially between projects crashes involving rear-end collisions typically increases as a examined in this research, even when stratified on the basis function of AADT in both daytime and nighttime periods, of time period (daytime or nighttime) and work condition the percentages are substantially lower in the nighttime (no work activity, active work without lane closures, or active periods. Furthermore, the percentage of rear-end collisions work with lane closures). Crash risks increased on some proj- increases noticeably during daytime work activity on low- to ects and decreased on others, compared to the expected values. moderate-volume roadways, but this is not so on higher- Furthermore, no relationship existed between the change in volume roadways. At night, rear-end collision percentages individual motorist crash risk and roadway AADT. increased during work activity across the entire range of road- Crashes that occur in nighttime work zones are not necessarily way AADTs. The effect is somewhat greater when temporary more severe than those that occur in similar daytime work zones. lane closures are in place than when they are not, consistent For each of the work conditions examined, the increases in with expectations.