Impact of Signal Timing Information on Safety and Efficiency of Signalized Intersections

Signalized intersections are provided in traffic networks to improve the safety and efficiency of vehicular and pedestrian movement. There are various measures under education, enforcement and engineering headings that are being attempted to improve safety and efficiency of operations at a signalized intersection. Provision of signal countdown timer, a timer showing the remaining red and green time in a phase, is one such measure and is commonly adopted in India. However, studies on effects of countdown timer under Indian traffic conditions are very scarce. Traffic heterogeneity and lack of lane discipline makes transferability of models developed in other countries (with more organized traffic) infeasible. The present study is an attempt to analyze the changes in queue discharge characteristics and red light violations (RLV) under Indian traffic conditions due to the presence of timer. A before and after analysis was carried out using the data collected from a selected intersection in Chennai, India. The analysis is carried out for different vehicle types in the presence and absence of timers separately for the start and end of red/green. Results showed that the information provided at the start of green (end of red) enhances efficiency, the startup lost time is reduced and there is an increase in red light violations. Two wheelers present at the start of the queue are found to be the category that is mostly affected by this information. However, the information provided at end of green (start of red) was found to reduce the red light violations. In the presence of information, it was found that the propensity of RLV (proportion of cycles having RLV) reduced from 59 % to 31 % at the end of green (start of red) and there was an increase from 12 % to 75 % at the start of green (end of red) with statistically significant drop in the headways (indicating an increased efficiency). Also, in presence of information, the intensity of RLV (Mean RLVs per RLV cycle) for both start of red and end of red reduced from 3.32 to 2.30 vehicles and 8.52 to 5.60 vehicles respectively. The impacts varied based on the vehicle types with major impacts on the two wheelers. The queue discharge models show a significant change in trend implying a need to update the signal timings when the timer’s are installed. These results also bring into light the trade-off between safety and efficiency and the choices drivers make in the presence of phase change information. These trade-offs should be carefully considered as the technology advances and drivers are provided more and more information. For example, with the advent of intellidrive technology (vehicle to infrastructure communications), the extent of information provided to the drivers should be tailored to achieve system optimality and results from studies such as the present one can help in decision making