Operation reliability for on-ramp junction of urban freeway

A disorder situation of traffic operation always appears in on-ramp junction area of urban freeway,because the operation action for vehicles presents the weaving condition,especially for different vehicle types.Based on the analysis on the cellular automata theory,and combining with on-site survey data,several key parameters were defined,namely,cellular length,cellular speed,cellular acceleration,updating time interval.In addition,cellular acceleration rule,cellular deceleration rule,random rule,lane-changing rule and other micro-simulation rules were set,and cellular automaton micro-simulation model was set up.Further-more,a micro-simulation module was developed for traffic operation actions of on-ramp junction with Matlab toolbox.Finally,a simulation experiment for traffic operation reliability was done with this micro-simulation module,and the situation of change for on-ramp junction area was obtained under the conditions of different mainline design speed,acceleration lane length,vehicle generation probability and lane-changing probability.The results show that operation reliability for on-ramp junction is determined by the parameters of the probability of vehicle generation and the length of acceleration lane,especially for on-ramp.

Efficiency promotion for an on-ramp system based on intelligent transportation system information

Effect of cars with intelligent transportation systems （ITSs） on traffic flow near an on-ramp is investigated by car-following simulations. By numerical simulations, the dependences of flux on the inflow rate are investigated for various proportions of cars with ITSs. The phase diagrams as well as the spatiotemporal diagrams are presented to show different traffic flow states on the main road and the on-ramp. The results show that the saturated flux on the main road increases and the free flow region is enlarged with the increase of the proportion of cars with ITS. Interestingly, the congested regions of the main road disappear completely when the proportion is larger than a critical value. Further investigation shows that the capacity of on-ramp system can be promoted by 13% by using the ITS information, and the saturated flux on the on-ramp can be kept at an appropriate value by adjusting the proportion of cars with ITS.

Traffic dynamics of an on-ramp system with a cellular automaton model

This paper uses the cellular automaton model to study the dynamics of traffic flow around an on-ramp with an acceleration lane. It adopts a parameter, which can reflect different lane-changing behaviour, to represent the diversity of driving behaviour. The refined cellular automaton model is used to describe the lower acceleration rate of a vehicle. The phase diagram and the capacity of the on-ramp system are investigated. The simulation results show that in the single cell model, the capacity of the on-ramp system will stay at the highest flow of a one lane system when the driver is moderate and careful; it will be reduced when the driver is aggressive. In the refined cellular automaton model, the capacity is always reduced even when the driver is careful. It proposes that the capacity drop of the on-ramp system is caused by aggressive lane-changing behaviour and lower acceleration rate.

Effects of the number of on-ramps on the ring traffic flow

Since ramps are an important composition of traffic systems and there often exist multi ramps in a tragic system, the number of ramps can have great effects on main road traffic and produce some complex phenomena. In this paper, we employ the model presented by Tang et al. [2009 Communications in Theoretical Physics 51（1） 71] to further study the effects of the number of on-ramps on the stability of traffic flow on a ring road. The numerical results show that this model can reproduce some complex tragic phenomena resulting from multi on-ramps on the ring road and the effects of the number of on-ramps on traffic flow, but the phenomena and the effects are both related to the initial density of the main road.

Combined bottleneck effect of on-ramp and bus stop in a cellular automaton model

The combined bottleneck effect is investigated by modeling traffic systems with an on-ramp and a nearby bus stop in a two-lane cellular automaton model. Two cases, i.e. the bus stop locates in the downstream section of the on-ramp and the bus stop locates in the upstream section of the on-ramp, are considered separately. The upstream flux and downstream flux of the main road, as well as the on-ramp flux are analysed in detail, with respect to the entering probabilities and the distance between the on-ramp and the bus stop. It is found that the combination of the two bottlenecks causes the capacity to drop off, because the vehicles entering the main road from the on-ramp would interweave with the stopping （pulling-out） buses in the downstream （upstream） case. The traffic conflict in the former case is much heavier than that in the latter, causing the downstream main road to be utilized inefficiently. This suggests that the bus stop should be set in the upstream section of the on-ramp to enhance the capacity. The fluxes both on the main road and on the on-ramp vary with the distance between the two bottlenecks in both cases. However, the effects of distance disappear gradually at large distances. These findings might give some guidance to traffic optimization and management.

A new targeted on-ramp control approach considering both efficiency and equity

On-ramp control is an effective approach for alleviating traffic congestion on highways.However,there is still a lack of on-ramp control approaches applicable to large regional highway networks.Here,we develop a targeted on-ramp control approach applicable to regional highway networks by taking advantage of the vehicle source information,which pinpoints the on-ramps contributing major traffic flow to the highway bottleneck.Furthermore,a combined and tunable controlling index is proposed to enhance the equity of the generated traffic control scheme.The proposed on-ramp control approach is validated on an actual large highway network using actual travel demand data.Results indicate that the proposed approach can well mitigate the traffic congestion of highway bottleneck while at the same time enhancing the equity and practicability of the generated traffic control scheme.

A dynamic speed guidance method at on-ramp merging areas of urban expressway considering driving styles

Dynamic speed guidance for vehicles in on-ramp merging zones is instrumental in alleviating traffic congestion on urban expressways.To enhance compliance with recommended speeds,the development of a dynamic speed-guidance mechanism that accounts for heterogeneity in human driving styles is pivotal.Utilizing intelligent connected technologies that provide real-time vehicular data in these merging locales,this study proposes such a guidance system.Initially,we integrate a multi-agent consensus algorithm into a multi-vehicle framework operating on both the mainline and the ramp,thereby facilitating harmonized speed and spacing strategies.Subsequently,we conduct an analysis of the behavioral traits inherent to drivers of varied styles to refine speed planning in a more efficient and reliable manner.Lastly,we investigate a closed-loop feedback approach for speed guidance that incorporates the driver’s execution rate,thereby enabling dynamic recalibration of advised speeds and ensuring fluid vehicular integration into the mainline.Empirical results substantiate that a dynamic speed guidance system incorporating driving styles offers effective support for human drivers in seamless mainline merging.

Queue Storage Design for Metered On-Ramps

Queue storage at a metered freeway on-ramp is an essential design element for metered on-ramps to prevent on-ramp queue from extending beyond on-ramps.In this paper,various existing methodologies that are used to size the queue storage at metered on-ramps were first reviewed.It was found that queue storage sized using 7%of peak hour on-ramp demand is widely accepted in practice.A limited dataset collected in California helps provide some reality check for this method.It is recommended that queue storage be recognized as an indispensable design element at metered on-ramps,and detailed sizing guidance be developed in the highway geometric design policy of the American Association of State Highway and Transportation Officials(AASHTO).

Hazard-based duration modelling of merging time interval on freeway on-ramps

Freeway on-ramps suffer high crash risks due to frequent merging behaviours.This study developed hazard-based duration models to investigate the merging time interval on freeway on-ramps based on microscopic trajectory data.Fixed effect,random effect and random parameters Weibull distributed accelerated failure time models were developed to capture merging time as a function of various dynamic variables.The random parameters model was found to outperform the two counterparts since the unobserved heterogeneity of individual drivers was captured.Modelling estimation results indicate that drivers along the merging section with an auxiliary lane perform a smooth merging process and are easily affected by speed variables.Dynamics of leading and following vehicles on the merging and target lanes are found to influence the merging time interval for merging without an auxiliary lane,whereas the influence of surrounding vehicles ismarginal for thosewith an auxiliary lane.The findings of this study identify potential countermeasures for improving safety during the merging process.

Controlling Congestion in Al-Seeb Highway Using Ramp Metering (Case Study)

This paper represents a case study of traffic congestion within a section on Al Seeb Street highway due to the on-ramp merging of vehicles that causes a bottleneck in the mainline road. It studies the efficiency of installing ramp metering within a ramp within the selected study zone. This is done by simulating the collected data using Vissim software by drawing three one-hour-long scenarios;the first scenario reflects the data collected for 30 minutes duration and is used as a base scenario to draw the other two scenarios, which are reflected as factored-up scenarios to create a situation observed in the early morning in the study zone at 6:00-7:00 in which slowing down of speeds exist, and breakdown is raised in working days. The two factoring-up scenarios were as follows: one without ramp metering and the other without ramp metering. Each scenario was calibrated and run five times with random seeds, and then the average was considered. The simulation examines the ability of RM to smooth traffic in mainline and reduce queuing on on-ramp roads within the selected study zone by comparing the performance of the network for the scenarios and comparing them in terms of the overall delays, number of stops and the average speeds for the vehicles within the mainline. The results showed a good performance reflected by the scenario with ramp metering with a reduction of the overall delay, a decrease in stops number and an increase of the average speed were achieved. For the base scenario, a visualization (video extracted from Vissim software) was extracted, showing no need to install RM with an associated table showing a number of stops equal to zero with an average speed of 102.74 km/h and a total delay of 6045 seconds. For the second scenario with no RM, a visualization was extracted showing a slowing down of speeds for vehicles within the mainline while vehicles merging from the on-ramp and need to be controlled with a table showing a number of stops equal to 16 and an average speed equal to 58 km/h and a total delay of 916,874 seconds. For the third scenario with RM, a visualization was extracted showing good control of the second scenario with a table showing the number of stops equal to 6, an average speed equal to 61 km/h and a total delay equal to 484,466 seconds. Ten literatures in regard to this study have been reviewed. The data collected are quantitative, which are collected using an indirect manual counting method and then the data is used to feed the software for simulation.

On-ramp merging strategy for connected and automated vehicles based on complete information static game

Improper handling of vehicle on-ramp merging may hinder traffic flow and contribute to lower fuel economy,while also increasing the risk of collisions.Cooperative control for connected and automated vehicles(CAVs)has the potential to significantly reduce negative environmental impact while also improve driving safety and traffic efficiency.Therefore,in this paper,we focus on the scenario of CAVs on-ramp merging and propose a centralized control method.Merging sequence(MS)allocation and motion planning are two key issues in this process.To deal with these problems,we first propose an MS allocation method based on a complete information static game whereby the mixed-strategy Nash equilibrium is calculated for an individual vehicle to select its strategy.The on-ramp merging problem is then formulated as a bi-objective(total fuel consumption and total travel time)optimization problem,to which optimal control based on Pontryagin's minimum principle(PMP)is applied to solve the motion planning issue.To determine the proper parameters in the bi-objective optimization problem,a varying-scale grid search method is proposed to explore possible solutions at different scales.In this method,an improved quicksort algorithm is designed to search for the Pareto front,and the(approximately)unbiased Pareto solution for the bi-objective optimization problem is finally determined as the optimal solution.The proposed on-ramp merging strategy is validated via numerical simulation,and comparison with other strategies demonstrates its effectiveness in terms of fuel economy and traffic efficiency.

Safety benefit of cooperative control for heterogeneous traffic on-ramp merging

The safety of heterogeneous traffic is a vital topic in the oncoming era of autonomous vehicles(AVs).The cooperative vehicle infrastructure system(CVIS)is considered to improve heterogeneous traffic safety by connecting and controlling AVs cooperatively,and the connected AVs are so-called connected and automated vehicles(CAVs).However,the safety impact of cooperative control strategy on the heterogeneous traffic with CAVs and human-driving vehicles(HVs)has not been well investigated.In this paper,based on the traffic simulator SUMO,we designed a typical highway scenario of on-ramp merging and adopted a cooperative control method for CAVs.We then compared the safety performance for two different heterogeneous traffic systems,i.e.AV and HV,CAV and HV,respectively,to illustrate the safety benefits of the cooperative control strategy.We found that the safety performance of the CAV and HV traffic system does not always outperform that of AV and HV.With random departSpeed and higher arrival rate,the proposed cooperative control method would decrease the conflicts significantly whereas the penetration rate is over 80%.We further investigated the conflicts in terms of the leading and following vehicle types,and found that the risk of a AV/CAV followed by a HV is twice that of a HV followed by another HV.We also considered the safety effect of communication failure,and found that there is no significant impact until the packet loss probability is greater than 30%,while communication delay’s impact on safety can be ignored according to our experiments.

Simulation Analyses of Two On-Ramp Lane Arrangements

Ramps are vital pieces of infrastructure connecting city traffic networks to freeways.The performance of a ramp is to some extent determined by the on-ramp lane arrangement.In this paper,our primary aim is to evaluate the performance in terms of travel time and vehicle emissions for two on-ramp lane arrangements:added lane and zip merging.We estimate the travel time and CO_(2) emissions on the basis of the speed,and acceleration of vehicles in accordance with the improved comprehensive modal emission model(CMEM),and then analyse the impacts of traffic volume and heavy goods vehicles(HGVs)on travel time and emissions.The impacts of main road traffic flow on travel time and emissions for the two on-ramp lane arrangements are analysed under scenarios with traffic volumes of 800,1000,1200,1400,1600 and 1800 vehs/h/lane.Meanwhile,the relationships between travel time,emissions and various proportions of HGVs(2%,4%,6%,8%and 10%)for both on-ramp lane arrangements are evaluated as well.We eventually present emission contour charts for the two onramp lane arrangements based on the possible combinations of traffic volumes and HGV percentages.

匝道单向板楼盖板的等效均布可变荷载确定方法

在仓储物流项目中,匝道楼板布置方式常以单向板楼盖为主。本文分别通过对物流货车轮压垂直和平行于单向板短跨行驶时的状态,根据简支板跨中绝对最大弯矩相等原则采用查表法对匝道单向板楼盖板的等效均布可变荷载进行计算和分析,为工程项目的设计提供经验参考。

苏州中南中心工程桩永临结合坡道设计与施工

超深基坑安全与施工进度息息相关,土方开挖与转运速度是基坑施工进度的重要影响因素。苏州中南中心项目利用前期工程试桩、试验锚桩及一柱一桩永临结合作为临时运输坡道竖向支撑,节约深基坑土方开挖过程中转土、吊土时间,有效加快施工进度,确保基坑安全,同时节约成本,取得良好综合效益。

大型工业厂房弧形上料汽车坡道关键施工技术

以绍兴市循环生态产业园(二期)焚烧厂工程为背景,针对弧形上料坡道施工中遇到的重难点,采取了一系列技术措施予以解决,主要包括弧坡测量信息化放线技术,金刚砂耐磨坡面一次整体浇捣成型技术,定制护栏模板支设应用技术等。通过应用这些技术措施,最终使得坡道混凝土成型质量高,坡道上部钢架被精准定位安装,最后取得了较好的应用效果并总结出一套完整的弧形坡道关键施工技术经验。

A modified weighted probabilistic cellular automaton traffic flow model

This paper modifies the weighted probabilistic cellular automaton model （Li X L, Kuang H, Song T, et al 2008 Chin. Phys. B 17 2366） which considered a diversity of traffic behaviors under real traffic situations induced by various driving characters and habits. In the new model, the effects of the velocity at the last time step and drivers＇ desire for acceleration are taken into account. The fundamental diagram, spatial-temporal diagram, and the time series of one-minute data are analyzed. The results show that this model reproduces synchronized flow. Finally, it simulates the on-ramp system with the proposed model. Some characteristics including the phase diagram are studied.

缓坡型小生物礁体的精细雕刻与“一井双礁”高产气井的突破——以川东地区长兴组小生物礁群为例

缓坡型生物礁具有侧向迁移、礁体规模小、离散状分布的地质特征,生物礁体精细雕刻难度大、生物礁气藏难以实现效益开发。为了破解上述难题,在深入认识缓坡型生物礁地质特征的基础上,提出了井震结合识别生物礁体的新方法并成功指导了四川盆地川东地区大猫坪Y012-X16井“一井双礁”的钻探,测试获得113.65×10^(4)m^(3)/d的高产工业气流,取得了生物礁气藏勘探的重大新进展。研究结果表明:①缓坡型生物礁台缘斜坡坡度仅2°~4°,礁体迁移演化规律主要受古地貌及海平面变化的控制,形成多排、多期的小礁体且缓坡型生物礁气藏气水界面不统一,具有“一礁一藏”的特征,礁体顶部含气性好,上二叠统长兴组二段早期礁体整体含气性较差,长兴组三段晚期礁体整体含气性较好;②创新形成以地震“双高”一体化处理技术、数据驱动的“盒状体”透视技术、残厚法沉积古地貌恢复技术和三维可视化技术为核心的生物礁识别新方法,实现了缓坡型小礁体三维空间精细雕刻;③应用生物礁识别新方法落实了大猫坪区块生物礁展布细节,建立了长水平段“一井双礁”开发模式,Y012-X16井刷新了中石油生物礁储层钻遇长度的纪录,为小生物礁群的效益开发开辟了新途径;④大猫坪区块预计可新增多个礁体开发区,可为气藏开发提供近100×104 m3/d的补充产能,具有较大天然气勘探开发潜力。结论认为,缓坡型小生物礁体的精细雕刻技术有助于对四川盆地缓坡型小生物礁群的识别和生物礁气藏的有效勘探开发。

城市快速路出口匝道瓶颈区域交通流率特征研究

分析城市快速路出口匝道附近的交通流率特征,对确定通行能力和提出管理措施具有重要意义.针对城市快速路线圈检测数据,利用方差分析和配对样本检验分析比较出口匝道瓶颈区域各车道之间交通拥挤前后的流率变化.发现内侧车道的交通流率在拥挤之前低于外侧车道,而在拥挤期间高于外侧车道.外侧车道在拥挤之后的排队消散流率会显著降低,而内侧车道的消散流率反而增加,即存在早发性交通拥挤的现象,并通过流量-速度关系图对内外车道交通流特征的差异进行阐释.

斜阶跃信号激励下的RLC互连线时延模型

文章对斜阶跃信号激励下的RLC互连线时延模型进行了研究。用改进1阶模型逼近传输线的传输函数,得到了比较简洁的时延解析式。该模型计算所得的结果与SPICE仿真结果的误差小于5%。