[Purposes] To quantitatively evaluate the impact of left-turning non-motor vehicle signal lights at urban intersections on traffic safety. [Methods] An evaluation method based on extended time to collision (ETTC) was proposed to assess the safety of left-turning non-motor vehicle signal lights. This study used video software to extract the microscopic vehicle trajectory data to calculate conflict indicators. In view of the existing time to collision (TTC) was not suitable for the evaluation of left-turning non-motor vehicles conflict at intersections, the improved TTC was used for the analysis of non-motor vehicle conflict. The extended time to collision considered the influence of vehicle dimensions and acceleration. The case study was conducted based on video data at 4 typical signalized intersections in Changsha, and used video trajectory tracking software to extract the conflicting trajectory data. [Findings] The install of left-turning non-motor vehicle signal lights provided a clear passing time for non-motor vehicles, which can significantly reduce the rate of non-motor vehicles conflict. Non-motor vehicles conflict rate of non-peak time and peak time was reduced by 40.11% and 25.27% respectively. At the end of the straight phase and when the left turn phase was about to light up, the left-turn non-motor vehicles in treatment groups wait in the waiting zone, and the conflict rate is 0; while near a half of non-motor vehicles had illegal left-turn behaviors during this period, leading to amounts of serious conflicts. The treatment effect (TE) of left-turning non-motor vehicle signal lights increases first and then decreased with the increase of non-motor vehicle flow. With the increase of motor vehicle flow, the trend of the treatment effect fluctuation gradually decreased. [Conclusions] This study revealed the influence of non-motor vehicle left turn signal on reducing traffic conflicts at intersections. It can provide useful reference for the control of non-motor vehicle traffic safety at signalized intersections.