Impact of Pedestrian Traffic on Saturation Rate of Protected Left-Turn at Urban Intersections

Yixin Chen,Xiaoduan Sun,Yulong He

doi:10.4236/ojapps.2015.51003

Yixin Chen, Xiaoduan Sun + Show 1 more

Open Access

https://doi.org/10.4236/ojapps.2015.51003

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Abstract

Heavily congested intersections in metropolitan areas in China are facing unique problems due to high travel demand and a high degree of traffic law violations. Based on a study conducted by the authors of this paper, 93% of left-turn vehicles turning left in these areas were slowed in order to avoid conflict with pedestrians. Intertwined pedestrian and vehicular flows can significantly reduce the capacity of exclusive left-turn lane group through reducing saturation flow rate, which increases the congestion at intersections. This paper investigates how the saturation flow rate of exclusive left-turn lane group is affected by the characteristics of pedestrian flow. By analyzing the imagery data collected by video cameras installed at intersections, the research team is able to obtain the characteristics of both vehicular and pedestrian flows, such as speed and spatial locations. The average operating speed at the saturation flow rate with and without pedestrian traffic is used as a direct measurement to evaluate the effect of pedestrians. Based on the statistical analysis, the paper concludes that saturation flow rate is mainly affected by the position of pedestrian in the crosswalk (inside or outside of left-turn vehicle’s trajectory), and the distance between the vehicle and pedestrians. In general, when the distance is less than four meters, the smaller the distance between vehicle and pedestrians, the larger the impact. However, there is no significant impact when the distance is larger than four meters. To accurately quantify the effect, the degree of pedestrian-vehicle impact is defined in four levels. The results show that the difference in the saturation flow rate between the best and the worst level could be 15.7%, which clearly indicates how important it is to enforce pedestrian crossing behavior.

Highlights

Signalized intersections in urban areas are problematic because of high travel demands and a high amount of pedestrians disregarding traffic signals
By investigating how the saturation flow rate is affected by illegal pedestrian crossings, this paper analyzes the imagery data collected at two intersections in Beijing, which show that pedestrians on the inside of vehicular flow affect the left-turn saturation rate the most
Based on the statistical analysis, the pedestrian influence is classified into four levels and the effect is quantitatively estimated at each level

Summary

Introduction

Signalized intersections in urban areas are problematic because of high travel demands and a high amount of pedestrians disregarding traffic signals. Based on our observations made at two typ- ical intersections in Beijing, about 63% of pedestrians at signalized intersections walk across the street while right-of-way is assigned by traffic signal to left-turning vehicles exclusively, and about 93% of left-turn vehicles are forced to slow in order to avoid pedestrians, undoubtedly affecting capacity of the lane group and aggravating traffic congestion problems. It is widely observed that more than 50% of pedestrians start walking across the street as soon as the signal turns green exclusively for left-turn vehicles. The speed slower than normal speed of left-turning vehicles could result in lower saturation flow rate. It is a serious problem for already heavily congested intersections in China

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