Driver behavior and gap acceptance studies at roundabouts

This thesis addresses drivers' gap-acceptance behavior characteristics at roundabouts and documents the measurement results of critical headway and follow-up headway based on selected roundabout sites in California. To measure these two parameters, video data were recorded and analyzed, and a computer program was developed to extract necessary gap events from the videos. The maximum likelihood methodology was applied in this study to calculate the critical headway, while the follow-up headway was obtained directly from the extracted time events. Raff's method was used to estimate the critical headway and compared with the result of maximum likelihood method. Comparisons were also made between the critical headway and follow-up headway results from California and those in other states. In addition, the factors affecting critical headway and follow-up headway were also investigated.; Statistical analysis did not show significant difference between the critical headway values in California and other states, while the follow-up headway measured at California roundabouts showed statistically difference from those obtained from other states. The conflicting flow rate was found to have a negative correlation with both critical headway and follow-up headway, and the speed of the circulating traffic was identified to have a negative correlation with critical headway and follow-up headway. The results from this study provide enhancement of the existing database related to drivers' gap-acceptance characteristics in the United States.