Urban Expressway Network Research Articles

Coordination Optimization of VSL Strategy on Urban Expressway and Main Road Intersection Signal

With the rapid urbanization during the past three decades in China, the urban expressway network has arisen with large numbers in many cities. However, the traffic conditions are becoming worse and worse. One of the main reasons is that the connected sections of main road and expressway do not have a coordination by the intersection signal and variable speed limits (VSL) on expressway. In this paper, a new cooperation optimization model of VSL on urban expressway and the intersection signal timing are proposed based on the mesoscopic traffic flow model. Its objective is to minimize the total delay and the number of parking. Its essence is adjusting traffic flow on the network in space-time so that the whole network can be in a state of equilibrium. It is effective to the control of local traffic congestion and can avoid the spread of congestion, thus improving traffic safety. Additionally, the optimal VSL strategy is proposed. And then a solution algorithm based on the simultaneous perturbation stochastic approximation (SPSA) is designed for the proposed model. In the end, a practical example of Yanshan overpass in Ji’nan elevated expressway is used to validate the effectiveness of the proposed method. The simulation results are satisfactory. The conclusions are very useful for traffic management department to implement reasonable traffic control strategy.

城市快速路网交通拥挤水平的非线性模糊综合评价研究

城市快速路网交通拥挤水平的非线性模糊综合评价研究

Implementing Congestion Tolls on Currently Free Highways With Public–Private Partnerships: What Are the Financial and Economic Benefits?

A trillion dollars in Interstate highway improvement and modernization work has been deferred due to lack of funding. More than half of Interstate and other freeway and expressway lane miles are classified as urban. Therefore, one approach that could be considered to generate needed revenue for freeway improvements in urban areas is implementing congestion-based tolls on freeways during peak periods when they are congested. Such an approach has been implemented in the Washington, DC metro area, on the I-66 freeway inside the Capital Beltway in Northern Virginia. This article demonstrates how an analyst may estimate the financial and economic benefits of a concept involving imposition of congestion-based tolls on the entire urban freeway network, during peak periods only, in conjunction with transit service improvements using automated transit vehicles. Furthermore, the article evaluates potential benefits from using a public–private partnership for implementation of the concept.

Comparative evaluation of measures for urban highway network resilience due to traffic incidents

Abstract The resilience of an urban highway network may be described as the ability for a highway network’s operation to adapt and rapidly recover from a disruptive event. Although the concept of resilience has been studied in the past decades, researchers have yet to agree on common measures of quantifying urban highway network resilience. This paper proposed five candidate measures of urban highway network resilience that are consistent with the concept of resilience triangle. They are derived from queue length, link speed, link travel time, frontage road delay and detour route delay, respectively. These measures were calculated from outputs of a mesoscopic traffic simulation model that mimicked the highway network in the El Paso, Texas region. Thirty scenarios were simulated, each with a complete link closure at a selected major highway location caused by a traffic incident. The results have shown that the five measures are not statistically correlated with each other, and the different measures produced different ranked lists in decreasing order of the impacts of the links closure locations. This means that using different resilience measures will lead to different conclusions in the order of disruption caused by the link closures. The outcomes supports the notion that a common measure of transportation highway resilience may not be necessary, and researchers may define their own resilience measures to meet individual project’s need.

A survey of model predictive control methods for traffic signal control

Enhancing traffic efficiency and alleviating &#x0028 even circumventing &#x0029 traffic congestion with advanced traffic signal control &#x0028 TSC &#x0029 strategies are always the main issues to be addressed in urban transportation systems. Since model predictive control &#x0028 MPC &#x0029 has a lot of advantages in modeling complex dynamic systems, it has been widely studied in traffic signal control over the past 20 years. There is a need for an in-depth understanding of MPC-based TSC methods for traffic networks. Therefore, this paper presents the motivation of using MPC for TSC and how MPC-based TSC approaches are implemented to manage and control the dynamics of traffic flows both in urban road networks and freeway networks. Meanwhile, typical performance evaluation metrics, solution methods, examples of simulations, and applications related to MPC-based TSC approaches are reported. More importantly, this paper summarizes the recent developments and the research trends in coordination and control of traffic networks with MPC-based TSC approaches. Remaining challenges and open issues are discussed towards the end of this paper to discover potential future research directions.

Expressway bottleneck pattern identification using traffic big data—The case of ring roads in Beijing, China

How to efficiently identify traffic bottlenecks in the expressway network and implement targeted measures is an important issue to mitigate traffic congestion. In recent years, with the proliferation of smartphones, smartphone-based navigation applications are receiving the worldwide popularity, which are being treated as an extremely rich source of traffic data. In this paper, we are devoted to proposing a novel approach to investigate traffic state and identify recurrent bottlenecks quickly and accurately from macroscopic network perspective, through fusing the data sources of fixed detectors and mobile navigation apps. First of all, this paper plots flow-speed fundamental diagram to derive critical speed, which is treated as the criterion to determine traffic state. Once the criterion has been established, typical bottlenecks in the entire expressway network can be efficiently identified through only utilizing smartphone-based probe speed data. Secondly, three pioneering indicators are put forward to quantify oversaturated traffic state and classify bottleneck patterns on urban expressway network. Applying this methodology, we take Beijing expressway network as a case to identify different patterns of bottlenecks, which are validated to comply with the reality. Moreover, the relationship between critical speed and the associated road segment features is explored and shows the possibility of predicting the critical speed even without flow data. As an end, some recommendations are proposed for improving different types of traffic bottlenecks.

Efectos de las autopistas urbanas en sus entornos inmediatos: un análisis desde la Sintaxis Espacial

La inauguración del túnel bajo la avenida Kennedy en octubre de 2017 en Santiago, transformó en vía expresa el último tramo de la autopista oriente-poniente de la ciudad que aún mantenía ciertas características de vía local. Con ello, se puso fin a la primera etapa de autopistas urbanas que entraron en funcionamiento hace ya 20 años y que han sido cuestionadas desde distintos frentes. Este trabajo busca profundizar en el análisis de los efectos (positivos y negativos) que la actual red de autopistas urbanas tiene en los barrios adyacentes, usando el marco teórico y metodológico de la sintaxis espacial.Para ello se analizaron las cuatro autopistas que penetran en el tejido urbano (Autopista Central, Costanera Norte, Acceso Sur a Santiago y Américo Vespucio), y tres escenarios: situación base, ciudad gratuita, y ciudad tarificada, considerando un buffer de 500 metros desde cada autopista para el análisis.Los resultados mostraron que la integración global o accesibilidad global de la red de calles, varió fuertemente en las cuatro autopistas analizadas, mientras que la integración local (accesibilidad a nivel de barrio) no muestra mayores cambios. Las variaciones a nivel global se explican por la forma en que fue intervenida la trama de calles vecinas a las autopistas: mientras en algunos casos se hizo un esfuerzo por generar continuidad entre ambos lados de la vía donde antes no la había (por ejemplo, Costanera Norte donde se construyeron nuevos puentes sobre el río Mapocho); en otros la intervención de las autopistas sobre la trama de calles tendió a dividir barrios que antes eran uno solo (por ejemplo Acceso Sur).Lo anterior muestra que los efectos negativos de las autopistas en los barrios pueden ser mitigados (en gran medida), con un adecuado diseño de las conexiones en sus bordes. Pasados 20 años desde la primera autopista urbana en Santiago, parece necesario que estas infraestructuras comiencen a ser evaluadas como proyectos urbanos con consecuencias en sus entornos.

Dynamic-model-based switched proportional-integral state observer design and traffic density estimation for urban freeway

In the face of the frequent occurrence of urban traffic congestion, only part traffic sensors can be utilized in the urban freeway, in order to more accurately estimate traffic densities and timely identify the congested road segments, a novel estimated algorithm of proportional integral state observer is proposed. Firstly, by embedding the Cell Transmission Model (CTM) into the Dynamic Graph Hybrid Automata (DGHA) framework, we model traffic flow over the urban freeway network. In modeling procedure, an urban freeway network is partitioned in term of three hierarchical structures which are freeway networks, links and cells, respectively. On the one hand, both the dual digraph of road segment structure and hybrid automata respectively are adopted to describe the freeway topology and the multi-modes of dynamic densities in road segments. On the other hand, a deterministic and reasonable constraint is used to reduce the number of combination modes, and thus the modeling procedure is modularized, rule-based and easily-extensible with the help of a combination algorithm. Therefore, the Piecewise Affine System (PWAS) model of the freeway network can be obtained. Secondly, In order to estimate the traffic densities of the urban freeway network, based on the dynamic model, we design a switched proportional integral state observer, and the observer design problem is transferred into the stability problem of the switching system. So the proportional gains and integral gains can be computed via introducing the Lyapunov function and using LMI technique, and thus the traffic densities can be estimated by the designed observer. Especially, the traffic congestion can be identified by checking whether the estimated densities are greater than the critical ones. Finally, a section of Beijing south third ring freeway as an example to verify the proposed approach, and the effectiveness and the feasibility are shown in the experiment results.

Optimizing location of variable message signs using GPS probe vehicle data.

A multi-objective optimization model is proposed to allocate the location of VMSs by maximizing the average traffic guidance utility of VMSs and the number of benefited links, while minimizing information redundancy. The traffic guidance utility is defined to quantitatively measure the value of an installed VMS, which is calculated from passively collected GPS data and the physical topology of road network. The number of benefited links is to measure how many links are covered by upstream VMS to disseminate information. Information redundancy is introduced to quantify the mutual impairing between any two VMSs. A heuristic search algorithm is developed to solve the optimization model, which can calculate the saturated number of VMS for a road network and optimize the project schedule of VMS installation process based on the proposed objectives. A real-world case study is conducted in Beijing to illustrate the validity of the proposed approach, where taxis are used as probe vehicles to provide GPS data. The results show the effectiveness of the proposed multi-objective optimization model and it is promising to use the emerging GPS data to help agencies to allocate the locations of VMSs on both urban roads and highway networks, instead of relying on the subjective judgment from practitioners.

Variable speed limit strategies analysis with link transmission model on urban expressway

The variable speed limit (VSL) is a kind of active traffic management method. Most of the strategies are used in the expressway traffic flow control in order to ensure traffic safety. However, the urban expressway system is the main artery, carrying most traffic pressure. It has similar traffic characteristics with the expressways between cities. In this paper, the improved link transmission model (LTM) combined with VSL strategies is proposed, based on the urban expressway network. The model can simulate the movement of the vehicles and the shock wave, and well balance the relationship between the amount of calculation and accuracy. Furthermore, the optimal VSL strategy can be proposed based on the simulation method. It can provide management strategies for managers. Finally, a simple example is given to illustrate the model and method. The selected indexes are the average density, the average speed and the average flow on the traffic network in the simulation. The simulation results show that the proposed model and method are feasible. The VSL strategy can effectively alleviate traffic congestion in some cases, and greatly promote the efficiency of the transportation system.

Decentralized State-Observer-Based Traffic Density Estimation of Large-Scale Urban Freeway Network by Dynamic Model

In order to estimate traffic densities in a large-scale urban freeway network in an accurate and timely fashion when traffic sensors do not cover the freeway network completely and thus only local measurement data can be utilized, this paper proposes a decentralized state observer approach based on a macroscopic traffic flow model. Firstly, by using the well-known cell transmission model (CTM), the urban freeway network is modeled in the way of distributed systems. Secondly, based on the model, a decentralized observer is designed. With the help of the Lyapunov function and S-procedure theory, the observer gains are computed by using linear matrix inequality (LMI) technique. So, the traffic densities of the whole road network can be estimated by the designed observer. Finally, this method is applied to the outer ring of the Beijing’s second ring road and experimental results demonstrate the effectiveness and applicability of the proposed approach.

공간통계기법과 내비게이션 자료를 활용한 도시부 도로 교통량 추정연구

교통량은 주말 및 첨두시 O/D 구축, 차량주행거리 산정, 혼잡도로개선 대책 등에 활용되는 중요한 기초자료이다. 그럼에도 불구하고 국내 도시부 도로의 교통량 링크 커버리지는 매우 낮아, 현재 수집 교통량으로는 교통정책 및 분석에 제약이 따를 수밖에 없다. 이에 본 연구에서는 특 광역시 중 수집교통량 및 속도의 링크 커버리지가 가장 낮은 서울시를 대상으로, 수집 교통량과 속도를 활용하여 교통량 결측링크의 교통량을 추정하는 방안을 제안하였다. 여기서, 교통량 추정 방법으로 공간적 통계기법을 활용하였다. 교통량 추정모형 구축시, 서울시의 도시고속도로와 도시부 도로는 교통류 및 통행패턴은 상이하므로 이를 분류하여 도시고속도로에는 구간별 상수함수, 도시부 도로에는 회귀크리깅을 적용하였다. 이용 데이터로는 서울시 TOPIS, 국교부 국가교통정보센터 등에서 수집한 공공부문 교통량, 속도와 민간 내비게이션 DB를 활용하였다. 내비게이션 DB는 대부분의 도로링크에서 수집되므로 교통량 추정에 매우 용이하다는 강점을 가지고 있다. 단, 내비게이션 DB는 수집 교통데이터의 샘플데이터이므로, 모집단인 교통량, 속도와 비교 검증하여 적용하였다. 뿐만 아니라 내비게이션 DB도 결측링크가 존재하고, 차종이 승용차로만 구성되어 있으므로 이를 보정하여 적용하였다. 공간적 통계기법을 통해 추정한 교통량은 MAPE, RMSE를 활용하여 실제 교통량과 비교 검증하였다. 검증결과 model error가 MAPE 6.26%, RMSE 5,410로 모델의 추정력이 높고, prediction error는 MAPE 20.3% 로 교통량 추정에 대한 추정력도 높은 것으로 분석되었다. 본 연구에서 제시한 교통량 결측링크의 교통량 추정모형은 차량주행거리와 온실가스 배출량 산정 등에 다양하게 활용될 수 있을 것으로 판단된다. Traffic volumes are fundamental data widely used in various traffic analysis, such as origin-and-destination establishment, total traveled kilometer distance calculation, congestion evaluation, and so on. The low number of links collecting the traffic-volume data in a large urban highway network has weakened the quality of the analyses in practice. This study proposes a method to estimate the traffic volume data on a highway link where no collection device is available by introducing a spatial statistic technique with (1) the traffic-volume data from TOPIS, and National Transport Information Center in the Ministry of Land, Infrastructure, and (2) the navigation data from private navigation. Two different component models were prepared for the interrupted and the uninterrupted flows respectively, due to their different traffic-flow characteristics: the piecewise constant function and the regression kriging. The comparison of the traffic volumes estimated by the proposed method against the ones counted in the field showed that the level of error includes 6.26% in MAPE and 5,410 in RMSE, and thus the prediction error is 20.3% in MAPE.

Modeling and Density Estimation of an Urban Freeway Network Based on Dynamic Graph Hybrid Automata.

In this paper, in order to describe complex network systems, we firstly propose a general modeling framework by combining a dynamic graph with hybrid automata and thus name it Dynamic Graph Hybrid Automata (DGHA). Then we apply this framework to model traffic flow over an urban freeway network by embedding the Cell Transmission Model (CTM) into the DGHA. With a modeling procedure, we adopt a dual digraph of road network structure to describe the road topology, use linear hybrid automata to describe multi-modes of dynamic densities in road segments and transform the nonlinear expressions of the transmitted traffic flow between two road segments into piecewise linear functions in terms of multi-mode switchings. This modeling procedure is modularized and rule-based, and thus is easily-extensible with the help of a combination algorithm for the dynamics of traffic flow. It can describe the dynamics of traffic flow over an urban freeway network with arbitrary topology structures and sizes. Next we analyze mode types and number in the model of the whole freeway network, and deduce a Piecewise Affine Linear System (PWALS) model. Furthermore, based on the PWALS model, a multi-mode switched state observer is designed to estimate the traffic densities of the freeway network, where a set of observer gain matrices are computed by using the Lyapunov function approach. As an example, we utilize the PWALS model and the corresponding switched state observer to traffic flow over Beijing third ring road. In order to clearly interpret the principle of the proposed method and avoid computational complexity, we adopt a simplified version of Beijing third ring road. Practical application for a large-scale road network will be implemented by decentralized modeling approach and distributed observer designing in the future research.

Evaluation of vehicle control algorithm to avoid conflicts in weaving sections under fully-controlled condition in urban expressway

Abstract: Weaving section is one of the major bottlenecks in urban expressway network. A field observation showed that approximately 80% of the weaving vehicles changed their lanes within the most upstream 25% part of the entire section length. It means an insufficient use of provided infrastructure, and strategies to use them are necessary. Then this study developed vehicle control algorithms to avoid conflicts in weaving sections and aimed to achieve the capacity improvement. The proposed algorithms were implemented into a microscopic traffic simulation model in order to evaluate their effects. Two types of weaving sections and several scenarios of weaving ratios were prepared. The amount of the throughput at the downstream section was counted and the lane change positions of individual vehicles were recorded. The result showed that the total throughput was decreased gradually as the weaving ratio was increased. However, this drop were improved significantly by applying some algorithms. This means that there is a potential to utilize the existing infrastructure more efficiently and to alleviate congestion without huge construction investment.

Research on the Macroscopic Fundamental Diagram for Shanghai urban expressway network

Abstract This paper are trying to investigate the existence and the characteristics of macroscopic fundamental diagram (MFD) for urban expressway network in different types of days based on detectors data in Shanghai, China. At first, the features of the urban expressway is discussed relating the speed and occupancy, and then the existence of MFD in Shanghai urban expressway network is proved based on one week’s data. Moreover, the hysteresis phenomena exist in most days and the network exhibits different hysteresis loops under different traffic situation. In order to explore the reason of hysteresis loops, all the detectors are categorized into seven types. When the free flow detectors are removed, the hysteresis loop also exist like the MFD of all the detectors. And when those detectors whose flow-occupancy relations exhibit similar hysteresis loop are removed, the hysteresis loop of MFD is not clear. Hence, they are proved to be the important part of all the detectors. And the hysteresis loop of individual detectors are influenced by shock waves and traffic situations. And the transitions of free flow traffic to congested traffic and the transitions of other way around are different. Hence, the fundamental diagram of individual detectors has significantly impact on the hysteresis phenomena of MFD. It is worthwhile to study the key detectors when the hysteresis of the MFD are discussed.

Correction of Bias Errors in Detected Traffic Volume on a Virtual Urban Expressway Network

Correction of Bias Errors in Detected Traffic Volume on a Virtual Urban Expressway Network

Continuity and change in American urban freeway networks

The American Interstate Highway System was created in 1944, though construction did not commence until 1956. During the planning process for this network the blueprint for American urban freeway systems was set in 1955 by a federal document called the Yellow Book. This provided about 100 maps of cities with planned urban freeway locations for the Interstate Highway System. A set of three basic network patterns were applied to these cities based on their size and location. In the half century since 1955 urban freeways in the Interstate System have expanded from a planned 2000miles to over 16,600miles, along with another 11,500miles of non-Interstate freeways. The number of large metropolitan areas has increased tremendously while the monocentric commuting patterns of have been transformed. This paper explores how these urban freeway systems were applied to the country's urban geography of the 1950s and how they have adapted to changing populations and other transformations in American metropolitan areas in the last half century.

Factors affecting vehicles’ carbon emission in road networks

ABSTRACTIn urban highway networks, some factors may influence the amount of average kilometric vehicle carbon emission (AKVC). Especially in highway networks of a large metropolitan area, the factors could be more diversified. In the present paper, the particular factors in the statistics of the districts in Seoul City that affect the AKVCs were investigated. Individual and combined factors were considered. The individual factors in the present study included the number of intersections, the number of intersections per kilometre, the road portion to the total area, the number of registered vehicles, the number of commuters, the population, the population density, the total land area and the road length. The combined factors considered included the number of intersections per kilometre over the number of registered vehicles, the number of intersections per kilometre over the road portion to the total area, and the road portion to the total area over the number of registered vehicles. Using the stepwise regression, it was demonstrated that the number of intersections per kilometre is the only significant factor affecting the AKVC in the road network of the district. All other factors are regarded as insignificant in affecting the AKVC. Additionally, correlation analysis confirms the result. From the study, as ‘the number of intersections per kilometre’ is the most influencing factor on reduction of vehicle carbon emissions in the road network, it may be implied that the number of intersections should be controlled or reduced in the road network of a city.

Congestion pricing strategies to investigate the potential of route diversion on toll facilities using en-route guidance

The application of intelligent transportation systems (ITS) technologies to facilitate the traffic mobility requires dynamic routing decisions. This study examines the effectiveness of Paramics, a microscopic traffic simulation model that uses a link-to-link shortest path algorithm to consider both updated link travel times and incident conditions detected through different traffic assignment techniques. This paper describes modeling of an urban highway network's traffic conditions to investigate potential route diversion through congestion pricing strategies on toll facilities in Orlando, Florida using Paramics. The experimental design included a multi-level factorial design with three qualitative variables and four response quantitative variables. The experiment's objective was to investigate different scenarios for reducing tolls on less congested roads (SR528 and SR417) and increasing tolls on more congested roads (SR408) to determine the impact on travelers' route choices and overall congestion in the network. The simulation results demonstrate that the Dynamic Feedback Assignment (DFB) led to a reduction in the average queuing delay and average travel time when compared to results from the Stochastic Assignment (SA). DFB significantly affected the percentage of diversion in the network. Drivers saved 10%–16% of travel time when DFB information was provided. Results also show that percentages of route diversion vary from one route to another and depending on the travel cost between specific origin-destination pairs. While drivers incorporate real time guidance information to maximize their own utility, not all drivers gain the same benefit. This was attributed to the limited extra capacity of the alternative routes and the longer travel distance. Combining congestion pricing strategies with traffic information maximize travel time benefits.

The Properties of Topological Network Connectivity Measures and Their Application to U.S. Urban Freeway Networks

The mathematical concepts of graph theory were introduced into geography in the early 1960s, providing a means of conceptualizing transport networks as made up of nodes and links. Among the contributions were several measures of topological network connectivity known as α (alpha), β (beta), and γ (gamma). These ratio measures identified the level of connectivity present in a network. These measures attracted considerable attention before fading from view, although they have recently returned to prominence in several applications. Despite this renewed attention, the basic mathematical properties of these measures remain largely unexamined. This research investigates the properties of these three simple ratio measures and explores values and properties that might be typical in urban freeway networks. Although simple correlation reveals little relationship between connectivity and freeway structure, they can be used to identify several groups of freeway networks as well as identifying important details about the use and interpretation of these measures. It is likely that these simple measures will continue to be applied to new situations, and this article provides some guidelines for those applications.