This study aimed at finding the effects of road geometry and cross-section variables on numbers of accidents. In addition, a methodology to combine variables by using decision trees was developed. Combination variables for road geometry and cross section were created by using the chi-square automatic interaction detection algorithm. Two negative binomial models were developed: one with homogeneous road segments and the other with 1-km road segments. Homogeneous road segments were divided on the basis of the horizontal alignment of the road. They were either curved or straight. The accuracy of the negative binomial model with homogeneous road segments was compared with that of the negative binomial model with 1-km road segments. The negative binomial model using homogeneous road segments was found to be the more accurate of the two models. The model with homogeneous road segments was used to draw conclusions with regard to the effect of variables on the number of accidents. Combination variables showed a significant effect on the number of accidents. The road geometry and cross-section variables were found to affect the number of accidents differently under various combinations of other variables.

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Work-related accidents at construction sites in Japan resulted in 1,001 fatalities and 44,886 injuries in 1996, but by 2005 the numbers had fallen to 487 fatalities and 27,193 injuries. In types of accidents at roadway work sites recorded between 1996 and 2000, traffic accidents ranked third. Since 2001, the Ministry of Land, Infrastructure, and Transport has sought to protect workers by mandating comprehensive improvements to uniforms of traffic control personnel, replacement of traffic control personnel with robots, more appropriate positioning of traffic control personnel, and placement of delta cushions. Research was done to contribute to safety at roadway work sites. Trucking companies and traffic safety contractors in Hokkaido were surveyed on their satisfaction with road safety measures. In addition, experiments were done at the Tomakomai Winter Test Track to evaluate the visibility of traffic control uniforms. For safety measures at roadway work sites, traffic safety contractors responded that items involving the upstream end of the work site (i.e., traffic control personnel placement and delta cushions) would most greatly influence their satisfaction. Trucking companies responded that ways of controlling traffic would most greatly influence their satisfaction. A portfolio analysis of customer satisfaction found that for both traffic safety contractors and trucking companies, ease of understanding of displayed construction information signs and nighttime visibility of traffic control personnel required priority improvement. Experiments on visual recognition of traffic control personnel identified the greatest recognition distances for fluorescent orange and yellow; the analytic hierarchy process identified the same result.

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