| Description |
Speeding-related crashes have contributed to a significant number of traffic-related fatalities throughout the United States. Previous analyses have indicated that small reductions in driver speed can significantly reduce the number of injury and fatal crashes. Many types of speed-reduction treatments have been tested and used. This study focuses on Optical Speed Bars (OSB). OSB are a low-cost speed treatment intended to cause drivers to reduce their speeds through alerting as well as perceptual cues. OSB have been tested using driving simulators and field applications. The results show statistically significant speed reductions. Although statistically significant, the magnitude of the reductions have generally been small in magnitude (with some exceptions). There are multiple field trials that have tested the speed reduction effects of OSB. Although many results have seen statistically significant speed reductions, it is difficult to compile, interpret, and draw conclusions regarding overall OSB effectiveness based on the separate published studies. There is a need to quantitatively combine previous results so that more direct conclusions can be made about the expected speed reduction effects of OSB. Meta-analysis is a methodology that can be used to quantitatively combine the results from multiple published studies. A meta-analysis combines results from multiple treatments and gives one overall expected effect for the treatment. This thesis applies a meta-analysis to estimate the overall expected speed reduction effects of OSB using field studies published from 2000 - 2013. Both fixed effects and random effects models are used. The data consisted of five published studies, 17 treatment locations, and 34 individual data collection points within those treatment locations. The overall speed reduction effects were then estimated through six different analyses. Each analysis looked at different characteristics of OSB (e.g., line style, alerting and perception cues, and the location of data collection points). Overall, speed reductions were statistically significant but were small in magnitude. This conclusion parallels many previous studies; however, the meta-analysis provided an expected speed reduction for all applications of OSB. Meta-analysis proved to be an effective methodology to combine and represent multiple published studies and is recommended for other speed treatment applications. |
