Work-zone safety on highway projects continues to be a national concern, and project safety performance is one of the indicators of project success. Contractors and State Transportation Agencies believe that expedited construction time under incentive contracting contributes to reducing the safety risk of road users travelling through work zones. Nevertheless, the truth of this belief has never been measured or supported by any statistical evidence. Obviously, understanding the impact of time-related incentive provisions on project-safety factors is important in order to provide better guidelines for the effective use of incentives, as well as for construction work-zone safety. Improving the current practice for time-related incentive provisions through the implementation of the research findings will provide the travelling public with increased value and safety. The goal of this research, therefore, is to investigate the statistical relationship between time-related incentive road construction projects and frequency of vehicle crashes in the State of California and provide project planners and managers with a better understanding of the impact of time-related incentive contracting on project safety performance. This research started with a narrow literature review with regard to time-related incentive contracting performances and work-zone safety studies. The research team also collected incentive and non-incentive project data from the California Department of Transportation (Caltrans). In addition, vehicle crash data was collected from the California Statewide Integrated Traffic Records System (SWITRS). Using Geographic Information System (GIS) software, the locations of construction projects and crashes at the project locations were then pinpointed on GIS centerline layers. Finally, statistical analyses were performed to investigate the relationship between the frequency and characteristics of crashes at incentive project sites and ones at non-incentive project sites in the State of California. The results of these analyses about how the current project incentive systems impact on construction work-zone safety were summarized. The research team successfully compiled data representing the locations of construction work zone and crashes using GIS technology and performed statistical analyses to compare the frequency of crashes at time-related incentive construction project site before, during, and after construction. An analysis of variance (ANOVA) test for both time-related incentive projects and non-incentive projects was performed to test if the occurrence of crashes is significantly different among three scenarios: 1) Before Construction, 2) During Construction, and 3) After Construction. The statistical analysis results for both projects show that the differences of crash occurrence among all three variables are not significant. This indicates that there is no adverse safety impact on time-related incentive contracting projects during the study period. No statistical evidence was found that time-related incentive contracting projects have a negative impact on work-zone safety performance. Although there was no work-zone safety difference among three scenarios, it is noted that the number of project data used for this study was small and limited. Only 19 time-related incentive projects and 13 non-incentive projects were collected and summarized in Appendix A and B, respectively. Approximately 10% of all incentive project data implemented in California has been collected during the research period and tested for this study. Therefore, in order to draw a more meaningful conclusion, it is necessary for the research team to collect more project data for each category and perform a statistical analysis with a large sample size. (Author/publisher)
Samenvatting