| Title | Effects of Speed limits on Crash Frequency in Freeway Tunnels |
| Year | 2018 |
| Degree | Master |
| School | Department of Transportation and Logistics Management National Chiao Tung University |
| Author | Shu Ming Hsu |
| Summary | The effect of tunnels’environment on crash frequency has no t been proved by empirical research or consensus model, and there are few crash researches about tunnels. Mo st researches treat tunnels as category variables. The focus of t his research i s on the effect measure ment of crash frequency by geometric design and traffic characteristics . D ifferent methods using transfor med variables were us ed to establish safety performance functions. After choos ing a better model, crash modification factors were applie d to measure its effect to crash frequency with in different range s of variable s . Different from before after crash modif ication factors, this study adopts variables’ baseline condition and measure s relative effect s in other condition s . Before establishing safety performance function, f ive models with different variable transform ation, includ ing original variable s , logarithm of annual average daily traffic, logarithm of annual average daily traffic and tunnel lengths, natural logarithm of annual average daily traffic, and natural logarithm of annual average daily traffic and tunnel lengths. L ikelihood ratio index and B ayesian Information Criterion were then applied to choose the model with better explanatory variable transform ation . The results show that the model with natural logarithm of annual average daily traffic and tunnel length is more better. E mpirical Bayesi an approach was applied to estimate the relationship between each speed limit and each lane numbers. By setting 90 km/h as the baseline condition, it appears that there are less crashes in 80 km/h and 100 km/h sections. By setting three lane as the baselin e condition, it appears that there are less crashes in two lane and four lane sections. |
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