Optimal allocation model of signalized intersections with dynamic use of exit lanes for left turn

In order to improve the operational efficiency of heavy left-turn demand intersections,an optimal allocation model of an intersection with dynamic use of exit lanes for left turns(EFL)is proposed.The constraints of setting EFL are analyzed,including the number and length of reverse variable lanes,flow direction constraints,and signal constraints,etc.The constraints and control variables are combined in a unified framework for simultaneous optimization.The objective functions are defined as the average delay and left-turn capacity of an intersection.The model is solved by a non-dominated genetic algorithm(NSGA-Ⅱ).The results show that after the optimal allocation of EFL,the average vehicle delays of the intersection can be reduced by 14.9%and left-turn capacity can be increased by 19.3%.The effectiveness of the optimal allocation model of EFL is demonstrated.

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

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.

信控交叉口借道左转设计的延误优化研究

为准确分析交叉口借道左转设计的左转延误,针对现有的延误模型的不足,建立一个合适的延误优化模型,并提升其设置的科学性。先对逆向车道长度进行优化;再通过分析左转车辆的累计到达驶离曲线,以左转总延误最小为优化目标,建立一种新的考虑预信号延误的优化模型;最后,以长沙市芙蓉中路一个交叉口为实例,进行验证,分析左转到达流率对借道左转设计延误的影响及逆向车道长度对左转车均延误的影响。研究结果表明:左转流率越大,越能充分发挥借道左转设计的优势,该模型的左转延误下降可达59.21%;当左转流量偏低时,预信号位置的延误占比较大,随着左转流量的增大,传统车道和逆向车道的延误占比逐步增加。该研究可以准确评价借道左转设计的实用性和优劣程度,对借道左转设计的推广与应用具有重要意义。

城市道路平交口左转专用车道类型及设计长度研究

为了解决城市道路平面交叉口左转车流引起的交通拥堵,提高交叉口的通行能力和安全水平,以十字形交叉口左转专用车道为研究对象,总结了城市道路平面交叉口左转专用车道的设计类型。针对当前国内平面交叉口左转车道设计长度不足的问题,选取典型交叉口对其高峰时段左转车流的转弯情况进行调查,根据运动学方程和车流波动理论推算向上游延伸的最长排队距离,从而提出左转专用车道长度的新算法。该算法考虑了车辆之间的传递性、延迟性、连续性特征,由其计算得到的设计长度可以减少左转车辆在交叉口引起的停车延误,提高交叉口的通行效率。

基于多目标配时优化模型和交通设计的城市交叉口协同优化研究

文章基于多目标配时优化模型和交通设计,旨在缓解城市道路交通拥堵。通过分析城市道路交叉口交通流特性和问题,关注交叉口车流流向、车流交织点以及配时合理性。在交通设计方面,提出将左转车道右置的渠化设计方案。在配时优化方面,建立了多目标优化模型,以延误、通行能力和停车次数为优化目标,以各相位有效绿灯时间、交叉口饱和度及周期时长为约束条件。通过遗传算法对模型进行求解,并用SUMO仿真软件评价求解结果。研究结果表明,交叉口的时空资源得到更有效的利用,明显缓解了交通压力,为城市道路交叉口的运行、管理和规划提供了参考。

信号交叉口借道左转设计方法研究

借道左转作为一种提高交叉口通行能力的交通管理措施,应用广泛。为了使借道左转的使用效果最优,总结借道左转的适用条件和实际运行的4个阶段,提出通过确定左转预信号相位和借道左转车道长度的方法,进行借道左转方案设计。首先,以单位时间借道左转的车辆数为评价标准,分析车道长度变化对借道左转实施效果的影响;其次,归纳出不同参数间的数学关系,得出最优借道左转车道长度与其他变量的转换方法,并推导出合适的左转预信号相位方案;最后,通过VISSIM软件仿真模型进行验证,证明设计方法的有效性。

城市道路应急车辆借道通行与信号协同优化模型

考虑单一的信号优先策略无法保证应急车辆不停车通过交叉口,因此,本文提出应急车辆借用逆向左转车道与交叉口信号协同优化模型。首先,在路段上通过应急车辆速度引导与逆向左转车道预信号配时的协同控制,优化应急车辆路段行驶速度,实现借用逆向左转车道通行;其次,增设应急相位保证应急车辆优先通过交叉口,以社会车辆出行总时间最小为目标,相位开启时间和绿灯持续时间为决策变量,考虑交叉口相位间的冲突、预信号开启和持续时间等约束条件,建立混合整数线性规划模型;并通过AMPL(A Mathematical Programming Language)编译并调用求解器求解,最后,以主干道和次干道相交的交叉口为例,对所提模型进行验证。结果表明:与绿灯延长模型相比,协同优化模型能显著降低应急车辆在交叉口区域的出行时间,减少社会车辆出行总时间。通过对流量和车道长度等参数的敏感性分析发现,随着流量和车道长度的增加,协同优化模型具有更好的优化效果。

Review of United States research and guidelines on left turn lane offset:Unsignalized intersections and signalized intersections with permitted left turns

The purposes of this paper are to better understand the design and impact of left turn lane offset and provide state transportation agencies recommendations on best practices and alternative design options to address left turn sight line obstruction issues.Research studies and existing guidelines on left turn lane offset were reviewed and summarized to offer insights in driver sight distance and behavior,intersection safety and operations,as well as design elements related to left turn lane offset.Studies showed that at both unsignalized intersections and signalized intersections with permitted left turns,obstructed sight line could cause higher possibilities of collisions between left turning vehicles and oncoming vehicles from the opposing direction.Existing evaluations of left turn lane offset,with data from multiple states in the United States,reported that positive left turn lane offsets were beneficial in terms of safety and operations.Most agency guidelines provided very limited discussions about left turn lane offset.This review demonstrated that positive left turn lane offsets are beneficial to intersection safety and operations.Based on the review of research and guidelines,recommendations were provided for transportation agencies for left turn lane offset implementation.A discussion on new left turn design concepts was also included to point out directions for future research and practice.

Safety effectiveness of roadway conversion with a two way left turn lane

In urban or suburban areas with a large number of access points, four-lane undivided highways are prone to crashes due to left-turning and through movements in a single lane. Many studies recommended expensive countermeasures like conversion from undivided to divided road with physical separation. One inexpensive alternative is reconfiguring the existing roadways by either increasing or decreasing the number of lanes. This study investigated the safety impact of converting four lane undivided roadways （4U） to five lane undivided roadways （ST） with a two way left turn lane （TIkrLTL）. This study used Empirical Bayes method to determine the safety impact of this inexpensive countermeasure. In this study, data from eight sites from Louisiana were collected for investigation, and site- specific crash modification factor （CMF） values were calculated. Although ST is usually not preferable due to its exposure of higher number of crashes in the existing literature, the findings of the current study indicated a positive safety impact. The benefit-cost ratio of this conversion ranges from 97 to 379. The current findings indicate that conversion of 4U to 5T is a feasible inexpensive solution for urban roadways with lower volume and a limited number of driveways.

Critical Conditions for Left-Turn Lane's Stop Line Backwards Setting Under Exclusive Left-Turn Phase

Aiming at the problem that the vehicles always turn left in advance which causes heavy conflicts in the intersection and effected traffic efficiency,the solution of the left-turn lane’s stop line backwards setting was proposed,and the critical conditions on the stop line’s setting were studied.Firstly,we studied the characteristics of trajectories distribution in the release process of turning left in advance vehicles.Based on that,we proposed to move the stop line backwards to solve the problem of turning left in advance.Considering the intersection’s geometric features and the vehicle operation features,the geometric critical condition was given for setting the position of left-turn lane’s stop line.And then the model of left-turn vehicles’queuing length was established based on queuing theory and traffic wave theory.By using queuing length model,the flow restrictions of stop line backwards could be found.Assuming left-turn vehicles’arrival rate is stable in a certain period of time,the minimum green time and the maximum red time of left-turn phase were given after the stop line was set up.According to the changes of the vehicles’turning paths,the shortest yellow setting recommendation was given.Finally,the application of the critical limits used in stop line backwards setting was demonstrated.The research result could provide a theoretical basis for traffic signs and markings’setting and perfect the relevant laws and regulations.

城市道路交叉口左转车道设置分析

城市道路交叉口作为路网的节点,承担了不同流向的车流和行人流。其中,左转车流对交叉口通行能力和交通安全的影响尤为重要。因此,对不同左转车道设置方式的车辆流线进行分析,发现采取“内移”的方式增设左转车道可以避免左转车辆和直行车辆交织变道;然后提出了一种可以变相“内移”左转车道的鱼腹形交通导流线优化设置方式,并借助VISSIM仿真软件对采用不同左转车道增设方式的交叉口通行能力进行了分析计算;最后以北京市某道路交叉口为例进行了仿真验证。分析结果表明:优化后的鱼腹形交通导流线在对左转车辆和直行车辆有序分流的同时,还能保证左转车道有足够的排队长度,较未设置鱼腹形交通导流线的车道,可在一定程度上降低交叉口总车均延误。

借对向出口车道左转交叉口交通控制方案优化

为提高借对向出口车道左转交叉口信号配时的科学性以及交通流运行效率,提出借对向车道左转的适用条件,将左转机动车的到达-驶离图式分为8种情况,分别建立每种情况下左转机动车的延误计算方法.以交叉口车均延误最小为目标,以周期时长、主信号与预信号各相位绿灯时间、借对向车道左转车道的长度为优化变量,建立了交叉口信号控制方案优化模型,并采用遗传算法进行求解.以算例的形式对所建立的优化方法进行验证,并与传统控制方法进行对比.结果表明:优化方法可以提高左转机动车通行能力,减少其所需绿灯时间,进而缩短交叉口周期时长;左转相位绿灯时间的缩短减小了直行相位的红灯时间,进而缩短了交叉口的车均延误,在高峰期交叉口车均延误下降比例达到23.8%.

城市道路两相位交叉口左转车道通行能力研究

以无信号控制交叉口可插车间隙理论为基础,分析了常见城市道路两相位信号控制交叉口左转车的交通流特性,建立了左转车道通行能力计算模型,通过实例对模型中的参数进行了标定。运用Vissim 3.6仿真软件对实际交叉口交通环境进行模拟,得到单位时间允许左转车通过交叉口进口道的最大车辆数,与模型计算所得通行能力值相比较,两者相对误差小于10%,从而证明所建立模型具有较强的适用性。

保护相位下左转车道存储段长度计算

以左转交通量、周期长度、左转绿灯时间为变量,运用排队论和概率论,从满足左转排队车辆停放需求的角度,对信号交叉口进口道设置为左转保护相位且仅有1条左转专用车道时的左转车道存储段长度展开研究.基于M/M/1排队系统,建立了保护相位下单条左转车道存储段长度计算的理论模型.在此基础上,讨论了模型的适用条件和实用性,分析了存储段长度随饱和度、左转交通量的变化规律,综合考虑空间几何条件、服务质量、经济性能,指出排队车辆数不宜超过20辆,当置信概率为95%时,实用饱和度区间为[0,0.8].讨论了置信概率、设计交通量及单位车辆停放长度等参数的取值方法.对典型情况计算、分析,提出极限交通量和极限排队长度、临界交通量和临界排队长度2组便于工程应用的概念,并绘制图表.制定了应用图表确定存储段长度的流程.该研究为交叉口采用左转保护相位且进口道仅设置1条左转车道的存储段长度确定提供了依据,修订后,也可以用于直行及右转车流排队长度和车道长度的计算.

平面交叉口左转车道的几何设计方法研究

针对平面交叉口左转车道的设计方法进行研究,参考发达国家平交路口安全设计规范,分析现有的设计技术规范中不合理的因素,从左转车道的布置、车道宽度的确定、车道长度的确定、过渡段的设计等几个方面,进行了详细的分析研究,提出了平面交叉口左转车道的几何设计方法。

基于逆向可变车道的交叉口公交左转优先方法

针对交叉口出口道时空资源利用不高的问题,以进口道公交左转优先为目标,提出了一种基于现有道路条件下的逆向可变车道及左转公交专用道设置方法从而实现了公交车辆的左转优先。分析了上述两种车道交叉口需满足的实施条件,并对车道进行设计,提出了相应的信号控制方法,最后结合设计案例,利用VISSIM软件对比分析了逆向可变车道设置前后交叉口的运行效果。仿真结果表明:设置后的管理方法能有效地降低本进口左转公交的车均延误及提高其通行量,且不影响交叉口其他方向车辆的正常通行,从而验证了本方法的有效性,为实现公交左转优先和减少出口道资源浪费提供了新的思路与方法。

共用左转车道通行能力比较分析

在不同车道配置、信号配时和直左交通量的情况下,将两种研究共用左转车道通行能力的方法(即1994《美国通行能力手册》和中国《城市道路设计规范》中的方法)进行了比较分析。结果表明:随着左转交通量的增加,共用车道的通行能力相应降低;当周期长从60s增加到90s,具有相同有效绿信比的进口道通行能力有所降低。具有相同总绿信比的长周期的通行能力略有增加;当左转交通量超过一个定值时,进口道的总需求交通量超过通行能力。改进信号相位相序,实施左转保护相位可解决这一问题。

考虑行人和非机动车的借道左转车道设置方法研究

针对借道左转交叉口交通组织方式,研究借道左转车道设置条件,提出了考虑行人和非机动车的主信号、预信号借道左转交叉口配时优化方法,以及进出口车道平衡度评价指标.以苏州市人民路-十梓街交叉口为例进行实证研究,并结合VISSIM仿真,对比分析优化前后交叉口中各车道的延误指标、平衡度指标及二者关联关系.结果表明:优化后交叉口各相位车均延误减少的同时,车道平衡度更加趋向合理,二者之间具有关联性,即延误指标和平衡度指标均能有效评价交叉口的运行情况.

信号交叉口左弯待转区对车辆排放的影响分析

为探究左弯待转区对信号交叉口车辆排放的影响,以左弯待转区长度和左转短车道长度为重要参数、以相位有效绿灯时间为决策变量,建立最小化车辆延误和交通排放的孤立交叉口信号配时优化模型。以大连市五一路/西南路交叉口为例,参考现状方案通过调整相位相序、增设左弯待转区、增设左转短车道获得5种优化方案。结果显示,在优化配时方案的前提下,能使车辆延误和排放减少的有效因素从高到低依次为增设左转短车道、调整相位相序、增设左弯待转区;对于相同的相位相序和渠化方案,只增设左弯待转区使车辆排放最少增加0.7%、停车次数最少增长14.8%、车均延误最少上升2.1%。研究表明,增设左转短车道比增设左弯待转区能更有效地减少延误和排放。

行人干扰对左转车流速度和加速规律影响及量化

中国信号交叉口中,机非干扰现象十分普遍.本文通过实际调查,以无行人影响的左转饱和车流为基础,通过显著分析方法,量化了行人位置(转弯车流内、外侧与距离)、人数对专用左转车流车速的影响,并根据严重程度将影响划分为4个等级,同时拟合了各级影响下排队车辆起步后的速度时间变化曲线.研究结果表明:(1)行人距车流距离是显著影响因素,而行人人数不是;(2)车流两侧同时有行人对饱和车流造成的影响,与其中较严重的单侧行人影响情况相同;(3)排队车辆在加速过程中的速度变化曲线呈'S'型,行人对车流影响越严重,车流加速到饱和流所需时间越长,饱和流车速越低,但不影响速度—时间曲线线型——'S'型.这些结论可为科学的交通管理奠定基础.