The Intermodal Surface Transportation Efficiency Act established a documentation procedure for crashes in work zones for daytime and nighttime operations. Yet the various crash databases maintained by state departments of transportation (DOT) and other agencies (for example, the Fatal Analysis Reporting System [FARS]) fail to yield data that can lead to explicit conclusions concerning the relative danger of nighttime construction operations versus daytime operations. The data are plagued by uncertainties on issues such as (1) the level of detail contained in the data, (2) the relationship of crashes to specific work zone locations, and (3) the variation in reporting practices. Cottrell, B.H., Jr., “Improving Night Work Zone Traffic Control,” Virginia Transportation Research Council, August 1999, concluded that, “although there is a perception that night work zones are less safe than daytime work zones, evidence to substantiate this perception, such as higher accident rates, was not available because of lack of traffic exposure data.” Information is needed to assess the characteristics of these crashes in both daytime and nighttime work zones. Subsequent research suggested that nighttime work zones have traffic-related crash rates up to three times higher than daytime work zones. If in fact nighttime operations are as dangerous as the data and perceptions suggest, more significant resources should be directed at ensuring worker and driver safety in nighttime work zones. The importance of this issue is magnified by recent operational efforts by DOTs to increase nighttime work operations in order to decrease work-zone traffic congestion. Under NCHRP Project 17-30, “Traffic Safety Evaluation of Nighttime and Daytime Work Zones,” researchers at the Texas Transportation Institute developed the crash rates for nighttime and daytime work zones; determined the nature of, and identified similarities and differences between traffic related crashes in nighttime and daytime work zones; identified and evaluated management practices that promote work zone safety and mobility; and developed work-zone crash reporting recommendations to further improve the data collected on work zone crashes. The New York State DOT work zone accident data base was used to conduct the analysis of the differences and similarities of traffic crashes and highway worker construction accidents occurring during nighttime and daytime periods in that state. Project work activity and crash data from 64 projects in California, North Carolina, Ohio, and Washington were also analysed to determine similarities and differences in crash risks experienced during nighttime and daytime operations. The researchers also critiqued and prioritised various highway agency management policies, procedures, and practices believed capable of mitigating work zone crashes and developed detailed recommendations regarding the collection and analysis of work zone crashes by highway agencies. Overall, working at night does not result in significantly greater crash risk for an individual motorist travelling through the work zone than does working during the day. In addition traffic crashes that occur in nighttime work zones are not necessarily more severe than those that occur in similar daytime work zones, when compared across similar work operations. The implications of these findings are that work activities that require temporary lane closures on moderate to high-volume roadways have substantially lower total safety impact to the motoring public if the work is done at night. The lower traffic volumes present on roadways at night result in a much lower number of crashes occurring over a work operation of a given duration. (Author/publisher) This report may be accessed by Internet users at http://onlinepubs.trb.org/onlinepubs/nchrp/nchrp_rpt_627.pdf
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