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7 driving population as a whole. Whereas the increase in crash Work Zone Accident database. This database is a one-of-a- risk to an individual motorist may, in theory, be greater at kind resource developed in the 1980s and expanded over the night than during the day, the much lower traffic volumes years, specifically for use in tracking all types of work-zone- (and thus vehicle exposure) that typically exist at a given related traffic crashes and worker accidents on NYSDOT con- location at night may more than offset this incrementally struction projects statewide. The database has been a valuable higher increased risk. Higher traffic volumes during the day asset to both NYSDOT personnel and other researchers in mean that the same number of crashes will produce much examining various questions about work zone features and lower crash rates per mvm. If the day versus night decision is crash characteristics that cannot be examined through tradi- for a given work zone, then it would appear that the practi- tional state traffic crash records and databases (42, 43, 44, tioner will want to minimize the number of crashes (assuming 45, 46). For this study, researchers explicitly examined the rel- equal severity). Thus, crash rate per mile of work zone would ative differences in the types and severities of traffic crashes and appear to be a better comparison metric. Certainly, differ- worker construction accidents during both daytime and night- ences in the severity of the increased crashes may also exist time work operations on New York freeway and expressway between daytime and nighttime work operations, which also facilities. Even more importantly, the database included spe- must be considered in the analysis. Together, this implies that cific information on various types of worker-involved traffic the use of additional crash costs, normalized on the basis of crashes and construction accidents sustained during both day the amount of work activity required at a given project loca- and night work activities; this is something that is not available tion, will most closely reflect the information that highway at the present time nationally in any other database. agencies must weigh in their decisions of whether or not to The second prong of the research effort was the collection work at night. and analysis of crash experiences of a four-state sample of Finally, although emphasis is traditionally placed on un- work zones. For some of the projects, work activities were derstanding and measuring the safety impacts of highway done predominantly during the daytime; for other projects, work zones to the motoring public, when considering the work activities were done mainly at night. For still other proj- differences between daytime and nighttime work operations, ects, some work activities were done during the day (mainly the consequences to highway workers also need to be taken those activities that did not require the temporary closure of into consideration. Unfortunately, very little data on this issue travel lanes), and other activities that required travel lanes to exist. The highway contracting community perceives work- be closed for several hours were performed at night. Four ing at night to be a significantly greater risk to workers than states were included in the analysis: working during the day. National databases (such as the Bureau of Labor Statistics) do not allow for a thorough com- California, parison of nighttime and daytime highway work condition North Carolina, safety. Data sources that provide at least some insight into dif- Ohio, and ferences in highway worker risks during these work periods Washington. are sorely needed. These states were selected because they provide access to their statewide traffic crash and roadway inventory databases Study Overview through FHWA's Highway Safety Information System (HSIS) Researchers ultimately adopted a two-pronged investiga- and because they reportedly had sufficient numbers of night tion for this research project, based on data sources available work projects ongoing during the time period of interest in to the research team. The first prong utilized the NYSDOT this study.