Abstract: In order to study the influence of pedestrian and bicycle groups on the semi-actuated signal timing algorithm, an analysis was made of the characteristics of left-turn vehicles crossing pedestrian and bicycle groups at two-phase intersections first. Then, based on the HCM 2000(highway capacity manual 2000) queue service time model, a new model for calculating the initial green signal time in the semi-actuated signal control algorithm was built using the critical gap theory and the principle of balance between the arriving and departing left-turn vehicles. Semi-actuated signal timing plan was computed with the proposed model using the data collected in Huairou District of Beijing, and was validated by evaluation of the level of service (LOS) using the index of signal control delay in the field experiment. The numerical test results show that the total control delay of the whole intersection decreases 37.8%, and the LOS improves from grade C to grade B, so the proposed model can make the signal timing plan more adapted to intersections with many pedestrian and bicycle groups.