Traffic Safety Evaluation of Nighttime and Daytime Work Zones (2008)

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

For work activities that require temporary lane closures, the total safety impacts to the motoring public are less if the work is done at night. Active work zones result in additional crash costs regardless of whether the work is performed during the day or at night. However, the amount of the increase is less if the work is done at night. This benefit of working at night, compared to doing the work during the day, extends across all AADTs, but it becomes much larger at higher AADTs. The severity of worker construction accidents is the same when working at night or during the day. The available data re- garding worker accidents did not allow a determination to be made as to whether such accidents are more frequent at night. However, the data do show that the accidents that do occur are no more severe at night than they are when they occur during the day. Management Policies, Procedures, and Practices to Improve Nighttime and Daytime Work Zone Safety Several strategies have the potential to substantially lower the increased crash costs resulting from work zones. Strategies that appear to offer the greatest potential for crash cost reduction include the following: • Practices to reduce the number and duration of work zones required; • Use of full directional roadway closures via median crossovers or detours onto adjacent frontage roads; • Use of time-related contract provisions to reduce con- struction duration; • Moving appropriate work activities (i.e., those that require temporary lane closures) to nighttime hours; • Use of demand management programs to reduce volumes through work zones; and • Use of enhanced traffic law enforcement. Other strategies may offer moderate reductions in crash costs due to work zones, depending on conditions. Strategies that have been grouped into this category include the following: • Designing adequate future work zone capacity into highways; • Use of full roadway closures that require traffic detours onto adjacent surface streets; • Use of ITS strategies to reduce congestion and improve safety; • Improvement of work zone traffic control device visibility; • Efforts to reduce flaggers’ exposure to traffic; and • Efforts to reduce workspace intrusions and their consequences—primarily at long-term, high-volume work zones. Work Zone Crash Data Elements, Collection and Storage Techniques, and Analysis Methods A need exists for both a state crash report form that includes the recommended MMUCC data elements and highway-agency- collected data elements for work zone crash analysis. Both approaches to obtaining work zone crash information have their advantages and disadvantages. The large amount of data that police officers investigating a crash must collect on the state crash reporting form limits how much specific detail about work zones can be included. In addition, certain types of technical data (type of devices in use, work zone design fea- tures in place, etc.) cannot be effectively judged by police per- sonnel who do not have this level of engineering expertise. Collection of this type of data by highway agency personnel is more appropriate. In addition, details about industrial accidents in the work area, something that is not typically in- vestigated via police crash reporting, can be better collected directly by the highway agency. The main drawback to high- way agency collection of crash data is that it may miss those crashes and accidents that occur when project staff are not onsite when the event occurs (weekends, rain days, periods of work inactivity, etc.). The crash report form data elements currently recommended in the MMUCC guideline provide a good starting point for establishing quality data on work zone crashes. Many of the rec- ommended data elements provide information that can be useful in assessing how work zones are affecting safety at both a project and process (regional or agency-wide) level. Some minor adjustments in several of the MMUCC data elements (changes to specific code descriptions and introduction of an additional work-zone-specific code) could further enhance the quality and quantity of crash data available to assess work zone impacts on traffic safety. Exposure data at work zones are particularly needed to im- prove process-level work zone crash analysis. Hours of activity (with and without lane closures or other capacity restrictions), traffic volumes, etc. are needed to allow consolidation across multiple work zones, to facilitate the computation of current benchmarks, to track safety performance against those bench- marks over time, and to allow possible comparison across regions and states. Work zone crash analysis procedures should include both monitoring and post-hoc analysis components. Monitoring procedures require quick access to crash data (the Ohio DOT manually collects hard-copy crash reports from law enforce- ment offices on a regular basis during a significant project) and a simple method of determining whether certain roadway segments or time periods in the project timeline are resulting in exceptionally more crashes than would be expected. These assessments serve as flags that the agency may need to evaluate 66

certain aspects of the work zone more closely. However, the more subtle effects of particular work zone design decisions or operating strategies can only be assessed through a more rigor- ous analysis across multiple projects and longer exposure peri- ods, typically after the projects have been completed. Recommendations The results of this research have led to a number of rec- ommendations that agencies should consider as they strive to improve work zone safety in their jurisdictions. In addition, a number of questions raised in this report have generated recommendations for future research that should be consid- ered as well. These are enumerated below: • At a minimum, agencies should evaluate their current poli- cies and procedures to encourage consideration of the fol- lowing strategies during design and implementation of work zones in their jurisdiction: – Practices to reduce work zone duration and number of work zones required; – Use of full directional roadway closures via median crossovers or detours onto adjacent frontage roads; – Use of time-related contract provisions to reduce con- struction duration; – Moving appropriate work activities (i.e., those that require temporary lane closures) to nighttime hours, especially on high-volume roadways; – Use of demand management programs to reduce vol- umes through work zones; – Use of enhanced traffic law enforcement; – Consideration of incorporating future work zone capacity into highway designs; – Use of full roadway closures that require traffic detours onto adjacent surface streets, where adequate capacity is available on alternative routes; – Use of ITS strategies to reduce congestion and improve safety; – Improvement of work zone traffic control device visibility; – Efforts to reduce flaggers’ exposure to traffic; and – Efforts to reduce workspace intrusions and limit their consequences at long-term, high-volume work zones. • Agencies should consider establishing their own data col- lection, archival, and analysis procedures for work zone crashes. The specific data elements to collect and the meth- ods used to collect those data will depend on what other data elements are already being collected through the state crash report form. Crash report forms that have most or all of the MMUCC data elements that were recommended for work zones in Chapter 5 may require agencies to collect only a few additional items in the event of a work zone crash. Crash report forms that do not include most of the key data elements identified will necessitate the collection of more of the data by the highway agency. In either case, it is important that both sources of data be accessible on a crash-by-crash basis to facilitate subsequent analysis. • For significant projects, agencies should consider estab- lishing procedures to monitor crashes occurring during construction in a way that allows agency personnel to quickly ascertain whether an excessive number of crashes are occurring at specific locations or during certain times within the project. • This research suggests that intrusion crashes, especially those that involve highway workers, are a relatively small subset of work zone crashes. However, when they do occur, they are more likely to result in injuries and fatalities to motorists, passengers, and/or highway workers. Additional research is recommended to further define the significance of the work zone intrusion crash problem and to conduct studies to determine the extent to which various proposed countermeasures reduce such intrusions. • Finally, this research has yielded a rich multi-state database of work zone, roadway, and crash data. Although extensive analyses of that dataset were performed as part of this re- search, there are likely many other questions about work zone crash safety that could be examined using these data. It is recommended that steps be taken to make these data available to other researchers or students looking for re- search topics related to work zone safety issues. 67