Quadruple left-turn lanes (QLL) are a popular design at major signalized intersections in metropolitan areas of China. At QLL intersections, traffic organization is extremely disordered; and a primary reason is frequent lane changes during left-turn (LCDL) behaviors. This study identified the contributing factors that cause LCDL behaviors at QLL intersections based on the observations of 192 green intervals and 550 individual lane-change behaviors collected in Changchun, China. A linear regression model was developed to predict the rate of lane changes during left turns (both inside to outside and outside to inside). In addition, a logistic regression model was used to estimate the probability of LCDL (inside to outside only) for an individual vehicle. Based on the two models, it was found that a long weaving distance (53–60 meters) tends to decrease the LCDL rate by 7.6% and the probability of individual LCDL behaviors by 18.2% when compared to a short weaving distance (22–29 meters). The initial lane that a lane-changing vehicle starting from was another factor that significantly contributes to the probability of LCDL. The most inside lane experiences the highest probability of LCDL (80.6%), followed by the second inside lane (60.4%) and the third inside lane (49.4%). Other significant factors include the left-turning traffic flow rate, the percentage of large vehicles, and the traffic flow rate on adjacent lanes (left and right). To reduce LCDL, some countermeasures were suggested for transportation agencies including engineering, enforcement, and education.