An Analysis of the Interactions between Adjustment Factors of Saturation Flow Rates at Signalized Intersections

Abstract

An insufficient functional relationship between adjustment factors and saturation flow rate (SFR) in the U.S. Highway Capacity Manual (HCM) method increases an additional prediction bias. The error of SFR predictions can reach 8–10%. To solve this problem, this paper proposes a comprehensive adjusted method that considers the effects of interactions between factors. Based on the data from 35 through lanes in Beijing and 25 shared through and left-turn lanes in Washington, DC, the interactions between lane width and percentage of heavy vehicles and proportion of left-turning vehicles were analyzed. Two comprehensive adjustment factor models were established and tested. The mean absolute percentage error (MAPE) of model 1 (considering the interaction between lane width and percentage of heavy vehicles) was 4.89% smaller than the MAPE of Chinese National Standard method (Standard Number is GB50647) at 13.64%. The MAPE of model 2 (considering the interaction between lane width and proportion of left-turning vehicles was 33.16% smaller than the MAPE of HCM method at 14.56%. This method could improve the accuracy of SFR prediction, provide support for traffic operation measures, alleviate the traffic congestion, and improve sustainable development of cities.

Investigation of saturation flow rate using video camera at signalized intersections in Jordan

“…It was not significant in both models with p-values equal to 0.930 and 0.843 for THMO and LUTM, respectively. On the contrary, previous studies concluded that lane width was significant in the SFR estimations [7,11,[17][18][19][20]. On the other hand, the number of lanes variable was significant in THMO-SFR, but not significant in LUTM-SFR model.…”

“…In China, several studies investigated the factors affecting SFR. It was observed that the lane width and turning radius [7], rainy weather [8], queue length [9], pavement markings [10], and lane width plus the proportion of heavy vehicles [11] were significant in the SFR estimations. Shao et al [7] estimated that the mean value of SFR based on 18 cities field measurements in China equals 1800 VPHPL.…”

Dynamic Estimation of Saturation Flow Rate at Information-Rich Signalized Intersections

“…The adjustment factor for turn radius and PCE (passenger car equivalents) were developed. Wang et al [7] and Lewis et al [8] found that there was an interaction effect between heavy vehicles and lane width. Wang et al [7] proposed a comprehensive adjustment factor for considering the interaction.…”

“…At present, researchers have proposed many estimated saturation flow rate models, which are mainly divided into the following three categories. One is a type of model based on the adjustment method in HCM [4][5][6][7][8] (see Section 2). In consideration of the traffic characteristics of different areas, they revise the existing adjusted factors and add new adjusted factors to improve the original adjustment model.…”

“…PoHV means the percentage of heavy vehicles 6. LW means lane width 7. MTL means multiple through lanes 8.…”