Study on Merging Sign Installation in Work Zone of Expressway Based on Changeable Critical Headway

The purpose of this research was to consider the vehicles’ changeable critical headway when driving along the upper work zone, and reducing conflicts and risks by merging in the end of the warning area, via installation of merging signage. A merging probability model was established by differential methods according to the M3 model and headway acceptance theory. According to the model, the appropriate position of merging signs was calculated in different traffic conditions. The influence of the merging probability by traffic parameters was analyzed, which indicated that the distance of merging signs had a positive correlation with the traffic volume; the distance of merging signs had a negative correlation with the proportion of free flow in the major lane; the distance of merging signs had a positive correlation with the vehicles’ speed in the major lane; the establishing of merging signs should be combined with the speed limiting.