Traffic Flow Speed Research Articles

DISTRIBUTION OF TRAFFIC SPEED IN DIFFERENT TRAFFIC CONDITIONS: AN EMPIRICAL STUDY IN BUDAPEST

Fundamental diagram, a graphical representation of the relationship among traffic flow, speed, and density, has been the foundation of traffic flow theory and transportation engineering for many years. Underlying a fundamental diagram is the relation between traffic speed and density, which serves as the basis to understand system dynamics. Empirical observations of the traffic speed versus traffic density show a wide-scattering of traffic speeds over a certain level of density, which would form a speed distribution over a certain level of density. The main aim of the current research is to study on the distribution of traffic speed in different traffic conditions in the urban roads since the distribution of traffic speed is necessary for many traffic engineering applications including generating traffic in micro-simulation systems. To do so, the traffic stream is videotaped at various locations in the city of Budapest (Hungary). The recorded videos were analysed by traffic engineering experts and different traffic conditions were extracted from these recorded videos based on the predefined scenarios. Then their relevant speeds in that time interval were estimated with the so-called “g-estimator method” using the outputs of the available loop detectors among the videotaped locations. Then different parametric candidate distributions have been fitted to the speeds by Maximum Likelihood Estimation (MLE) method. Having fitted different parametric distributions to speed data, they were compared by three goodness-of-fit tests along with two penalized criteria (Akaike Information Criterion – AIC and Bayesian Information Criterion – BIC) in order to overcome the over-fitting problems. The results showed that the speed of traffic flow follows exponential, normal, lognormal, gamma, beta and chisquare distribution in the condition that traffic flow followed over-saturated congestion, under saturated flow, free flow, congestion, accelerated flow and decelerated flow respectively.

Time Headway as Indices of Traffic Congestion

Urban mobility problem in Nigeria is on the increase, due to rapid growth in traffic that is not matched with the existing transport infrastructure, resulting in traffic congestion. Headway, a measure of level of service of a roadway, could be instructive in addressing this problem, hence this study. Headway, traffic flow and travel speed were collected for morning and evening peak periods for three consecutive weeks for two selected sections of a road in Ile-Ife, Osun state, using normal procedure. The obtained headway data were subjected to statistical analysis. Headway models were developed using regression analysis and the developed models were evaluated using Adjusted Coefficient of determination (R2). The results showed that the traffic along the road was heterogeneous. The maximum safe speed (85th percentile speed) was 31.20 km/hr, while the minimum allowable speed (15th percentile speed) was 28.50 km/hr. The ratio of flow to capacity (v/c) of the road was 0.65 and thus characterised to operate at level of service C. The headway models were h =0.001n2 -0.418n2 + 35.401, h = 0.002n2 – 0.569n + 42.122 , R-square values of 0.942 and 0.928 and minimum headway values of 5.35 sec. and 5.52 sec. For sections one and two respectively. The road is therefore prone to congestion.

Influence of Large Vehicles on the Speed of Expressway Traffic Flow

Large vehicles impact the quality of traffic flow. To predict the impact of large‐scale vehicles on the average speed of traffic flow, vehicle speeds under different vehicle mixing rates were collected through field observations. A laser roadside traffic survey instrument with automatic vehicle type identification functionality was used to collect cross section traffic flow data. The v/C ratio, large vehicle mixing rate, and average speed of traffic were calculated for each data set. A total of 158 traffic flow data sets were captured and divided into three groups according to the v/C ratio of the expressway. The v/C ratio ranges of the three groups are v/C ≤ 0.35, 0.35 < v/C ≤ 0.55, and 0.55 < v/C ≤ 0.90. SPSS software was used to analyze the correlation between the vehicle mixing rate and the average speed under different traffic flow conditions, and a model was determined between the average speed of the vehicle flow and the large vehicle mixing rate. Analysis of the results with SPSS revealed a negative logarithmic linear relationship between the average traffic speed and the mixing rate of large vehicles. The results could also be applied to passenger cars. The models are considered as corrections of the average speed of the traffic flow after the mixing of large vehicles. When the mixing rate of large vehicles is close to zero, the forecast value of the model is the average speed of passenger cars. Furthermore, as the traffic volume of the road section increased, the influence of the mixing rate on traffic flow speed became more obvious. The adaptability of the proposed prediction model of the expressway mixing rate was verified by evaluating model predictions against actual measurements.

Multiplicative method for creating the traffic monitoring base in a megapolis

The purpose of the study is the development of methods of identification of vehicles. These methods based on the system of identification their optical images for organization of movement and reducing the number of road accidents. There is a way of mathematical processing of signals in this method. These signals are registered with the help of optical-electronic sensors for the rapid decision-making based on computer technology. As a result, there is a confirmation of the method’s operability in real conditions. Digital signal processing lets to determine the intensity, speed and density of traffic flow automatically. At the same time, multiplicative method is a method of multidimensional analysis in a multidimensional space of numerical criteria. It divides the traffic flow by classes. This technology opens a lot of great opportunities for optimizing traffic management and helps to improve the safety of vehicles. The results of the survey are proposed for using in smart city systems.

Analysis of the Relationship between the Number of Traffic Accidents and the Traffic Flow & Section Location in Extra Long Tunnel

In order to study the influence of the traffic characteristics on traffic accidents in extra long tunnel, the main measurement indicators of traffic flow during the time of traffic accidents are matched with the accident information to form a data set of the number of traffic accidents and the hourly traffic flow of the accident. Vehicle ratio and the number of accidents are mainly used as the characteristic indicators of traffic flow. At the same time, the longitudinal distribution law of the average speed of traffic flow and the number of traffic accidents in the extra long tunnel is studied. Based on the superposition principle, the extra long tunnel is divided into 5 traffic safety zones. This paper analyzes the distribution of time, morphology, cause of accident, and other characteristics in different traffic safety zones, finding that the shape of traffic accidents in extra long tunnel is mainly rear-end collisions. Improper operation and illegal lane changes are the main causes of accidents.

Investigation of transport flow delay at unsignalized intersections with limited speed

Introduction. Many studies have argued that traffic delays at unregulated intersections depend on the intensity of the main flow and the intensity of pedestrian flow. Purpose. It is proposed to investigate traffic flow delays using the VISSIM software environment at unsignalized intersections at different flow rates. Results. Areas of the street and road network for experimental research were selected in the central part of Lviv. Triangles of visibility distance are calculated, problem places where it is necessary to establish a road sign 3.29 “Limitation of the maximum speed of movement” are defined. An analysis of existing methods for determining traffic delays at unregulated intersections is carried out at the paper. The method of estimating the average speed of traffic flow and the method of simulation modeling of transport flows in order to build a theoretical model are presented. The analysis of the dependence of the change of transport delays, obtained based on measured actual data and the method of modelling traffic flows, is carried out. The visibility distance for each intersection is calculated taking into account the speed mode. Graphical dependences of the change of the average and maximum length of the queue of vehicles under different modes of traffic light regulation in the secondary direction are given. It is determined that the average flow speed varies from 17 km/h to 38 km/h when changing the maximum speed limit from 15 km/h to 40 km/h. It is established that the lowest average traffic delay at unregulated intersections is observed at a traffic flow speed of 30 km/h. Conclusions. The substantiation of the introduction of the recommended speed regime on sections of streets with limited speed is given which takes into account transport delay, queue length, geometric parameters of the street, the presence of public transport stops and pedestrian crossings, traffic intensity and composition. The proposed method of controlling secondary traffic flows at unsignalized intersections, allows to increase traffic safety when traveling in secondary vehicles.

On the Use of Glint-Doppler-Azimuth Correlation for Speed Estimation of Nearby Tangential Targets

This article introduces a new radar architecture, which implements a new signal processing scheme, with applications to the Intelligent Transportation Systems. The proposed solution exploits a well-known problem regarding low range radar systems, the Glint Effect, in order to improve previous results. For that purpose, the presented system is required to measure azimuth and Doppler of targets, for which it opts for a 2-channel Digital Array Receiver scheme working with a frequency-modulated continuous wave. This involves more complex hardware and signal processing software, comparing to the common mono-channel non coherent systems, nevertheless latest devices (radio frequency subsystems, field-programmable gate arrays, digitizers, etc) make it simple and affordable. The proposed system, with an easy-and-fast side-looking installation, exploits several advantages of its 2-channel synchronous architecture (e.g. clutter cancellation, Doppler history availability, etc) to achieve a better estimation of two key measurements: traffic flow (instantaneous and average) and vehicles speed.

Simulation and modeling traffic flow based on Division K Nearest Neighbor

A new traffic flow model is proposed based on cellular automata and Division K Nearest Neighbor for the predication problem of traffic flow state change trend. The model firstly gives the update rules of vehicle state evolution and lane change rules of a vehicle, and establishes the state prediction model based on Division K Nearest Neighbor. Finally, the simulation analysis is conducted by the use of experimental platform, and the relationship between the factors such as average traffic flow speed, average flow rate, traffic flow density and lane change frequency, etc. is deeply studied. The results show that the prediction model has great advantages in the medium and low density area, and lower lane change rate has limited effect on the improvement of traffic flow.

Recruitment and entropy decrease during trail formation by foraging ants

Social insects utilise a complex spatial orientation system mediated by chemical signals. This study investigated how the foraging behaviour of ants (Dorymyrmex thoracicus) varies depending on the quantity of an available resource using a field experiment. Further, we demonstrated computationally that ant displacement is compatible with a model based on pheromone deposition. Our experiment tested how the resource size (large or small) and availability (one or two simultaneous patches) of resources offered influence the number of recruited ants (traffic flow) and the speed of traffic flow both moving towards a resource and returning to the colony. The results showed that the returning flow was higher than the going flow independent of resource. The traffic flow towards a single resource was higher than the flow for either of two simultaneous resources patches offered; thus, multiple resources sources split the flow, regardless of the fact that resource size did not affect foraging choices. Our results indicated that the ants used an orientation mechanism that can be reproduced by a theoretical computer model. With our model, we showed that initially, the displacement of ants followed no clearly detectable pattern. However, with increasing levels of ant recruitment and consequent pheromone deposition on the most used trails, returning displacement revealed the formation of shorter and more organised trails. The model revealed key transition between periods of order and disorder that continued until the flow of information reached an organised state (Shannon entropy). This study highlights an exceptional mechanism of foraging optimisation in eusocial insects.

The Effect of Brick and Granite Block Paving Materials on Traffic Speed.

Slowing traffic speed in urban areas has been shown to reduce pedestrian injuries and fatalities due to automobile accidents. This research aims to measure how brick and granite block paving materials, which were widely used historically prior to the use of asphalt paving in many cities, may influence free flow traffic speed. Traffic speeds for 690 vehicles traversing street blocks paved with asphalt, granite block, and brick materials were measured using a radar gun on a sample of 18 matched pair (asphalt and historic paving material) street blocks in Philadelphia, Pennsylvania. Fixed effects linear regression was used to estimate the effect of paving material on vehicle speed after controlling for the street class (e.g., arterial versus local road) and the matched pair. Results indicate that brick reduced speeds by approximately 3 mph (~5 km/h) and granite block reduced speeds by approximately 7 mph (~11 km/h), as compared to asphalt paved city streets, which we attribute to drivers intentionally slowing due to road roughness. This research suggests that brick and granite block paving materials may be an effective traffic calming strategy, having implications for reducing negative health outcomes associated with pedestrian–automobile collisions.

NEW APPROACH TO ADDITIONAL LEFT-TURN SECTIONS OF THE TRAFFIC SIGNAL REGULATION

Introduction. The paper describes methods of using the additional left-turn phase of regulation. The authors view the main foreign and domestic methods used in the specialization of the left turn in a separate phase of regulation. To propose a new approach to the specialization of the left-turn direction in a separate phase of regulation the authors investigate one of the most loaded intersections in Voronezh and determine the main characteristics of the traffic flow. Therefore, the authors suggest new parameters in choosing of the necessary method of traffic organization at controlled intersections.Methods and materials. The paper analyses the main methods, which were conditionally related to two approaches: the accident rate of the site and the characteristics of the traffic flow (speed and intensity of the left-turn flow). The authors explained that the new approach, which took into account such parameters as speed, vehicle delays and queue length, allowed effectively controlling the intersection due to the optimal choice of the necessary traffic organization method and due to the result of changes in the parameters by combining the intensity of the left-turn flow and forward flow.Results. The authors developed the approach to the additional left-turn section introduction at the controlled intersection based on a comparison of the left-turn intensity and forward flow and on the analysis of changes in the main characteristics of the traffic flow (speed, vehicle delays and queue length).Discussion and conclusions. The authors concluded that it is necessary to use the proposed approach at the stage of modeling, design and reorganization of the regulated area on the basis of changes in the main characteristics of the traffic flow.

Modeling of the Relationship Between Speed Limit and Characteristic Speed of Expressway Traffic Flow

Understanding the relationship between speed limit and characteristic speed of expressway traffic flow is of great significance for formulating a reasonable speed limit scheme and improving highway safety and transportation efficiency. In this study, the speed data of the same traffic flow passing through speed limits of 80, 100, and 120 km/h were continuously collected through a field test. The 85th, 15th, and 50th percentile speeds were considered the characteristic speed parameters of the traffic flow. A regression analysis was performed to establish a relationship between the characteristic speed parameters of the traffic flow and the speed limit. Under a free-flow state, the characteristic speed exhibited a strong linear relationship with the speed limit, where the variation ranges of the 85th and 50th percentile speeds were approximately consistent with that of the speed limit. However, a slight inconsistency was found for the 15th percentile speed, which was approximately half the speed limit increase; under a non-free-flow state, the correlation between the speed limit and the vehicle speed was no longer significant.

The impact of the average traffic flow speed on occurrence risk of road crash

Traffic flow characteristics have a significant impact on occurrence risk of road crash. The most important characteristics of the traffic flow, the impact of which is the subject of numerous studies, are the traffc flow, density, average traffic flow speed, dispersion of traffic flow speeds, as well as the contents of vehicle in traffic flow. These characteristics are in strong correlation between each other, so changes in one parameter conditional make change of other parameters. Research shows that speed-related traffic flow parameters have a significant impact on occurrence risk of road crash. Therefore, in this study an analysis of the impact of the change in the average speed of the traffic flow on the risk of an accident occurred. The research includes a section of the single carriageway from Preljina to Ljig. After the construction of the highway in the stated section of the signle carriageway, a change in the characteristics of the traffic flow occurred, with this study examining the impact of changing the average speed of the traffic flow to the occurrence risk of road crash. The connection between the speed of traffic flow and the risk of accidents has been confirmed in this study, so with the increase in average speed the risk of accidents increases.

The Effect of Posted Speed Limit on the Dispersion of Traffic Flow Speed

Speed dispersion is an important indicator to portray the quality of traffic flow and is closely related to the road safety operation level. In order to clarify the influence of posted speed limits on the dispersion of traffic flow speed, three sections with speed limits of 80 km/h, 100 km/h and 120 km/h on the same expressway were selected for observation, and traffic volume, speed and other parameters were collected. The characteristic speeds, such as average speed, V15 and V85, were evaluation indicators, where V15 and V85 are the speeds of the 15th and 85th percentiles measured at the feature points of the road when the traffic is in a free-flow state and the weather is good. The relationship between different posted speed limit values and the above indicators was analyzed using the statistical analysis software, SPSS. The results show that the speed limit has a high correlation with the average speed of traffic flow, V15 and V85 in free-flow state, with the coefficient of determination being as high as 0.84, 0.85 and 0.92, respectively. In the restricted flow state, the factors affecting the driver’s driving speed are mainly the decrease in driving freedom caused by the increase of traffic volume rather than the speed limit value. In a free-flow state, when the posted speed limit is increased and the average speed and the V85 also increased by approximately the same magnitude. The posted speed limit values of 80 km/h, 100 km/h and 120 km/h correspond to the 90, 88 and 97 percentile speeds of the traffic flow, respectively. The higher the speed limit is, the larger the speed difference between V15 and V85 becomes. The results of the study are very useful for rationally determining the speed limit scheme under different traffic flows.

Left-Side On-Ramp Metering for Improving Safety and Efficiency in Underground Expressway Systems

As one of the effective measures of intelligent traffic control, on-ramp metering is often used to improve the traffic efficiency of expressways. Existing on-ramp metering research mainly discusses expressways with right-side on-ramps. However, for underground expressway systems (UESs), left-side on-ramps are frequently adopted to reduce the ground space occupied by ramp construction. Since traffic entering from the left and right sides of the mainline may have different traffic characteristics, on-ramp metering for UESs with left-side on-ramps should be explored specifically. This study examines the impacts of left-side on-ramps on the traffic safety and efficiency of UESs and proposes an effective on-ramp metering strategy. Firstly, using field data, traffic flow fundamental diagrams and speed dispersion are discussed to explore the traffic flow characteristics of the “left-in” UES. The results show that the capacity and critical occupancy are both reduced in left-side on-ramp compared to right-side on-ramp expressways. Meanwhile, the speed dispersion is higher in left-side on-ramp UESs, which means a higher accident risk. Based on this, considering traffic safety and efficiency, a novel two-parameter left-side on-ramp metering strategy for UESs is proposed, in which occupancy and speed are used as the control indicators simultaneously. Additionally, the mechanism of the metering strategy is explained. Finally, the proposed on-ramp metering strategy is simulated on a real UES. The results demonstrate the advantages of the proposed two-parameter on-ramp metering strategy for improving the traffic safety and efficiency of UESs.

Adaptive Rolling Smoothing With Heterogeneous Data for Traffic State Estimation and Prediction

Spatial–temporal traffic state estimation and the prediction of urban expressways is a vital component of traffic management and information systems. The adaptive smoothing method is one of the most frequently used approaches to estimate traffic states. However, the fixed filter parameters used in existing approaches sometimes fail to characterize traffic dynamics well. To better capture generation, propagation, and mitigation dynamics of traffic congestion, we propose an adaptive rolling smoothing (ARS) approach by dynamically tuning the filter parameters in a rolling horizon scheme for online applications. The fusion of heterogeneous traffic data combines aggregate traffic measurements (e.g., traffic flow rate, time occupancy, and speed collected by remote microwave sensors) and disaggregate information (e.g., timestamps of individual vehicles detected by license plate recognition cameras). A nonlinear traffic flow filter based on the virtual trajectory algorithm is established to reconstruct the spatial–temporal traffic state and estimate experienced travel times of individual vehicles. The results demonstrate the capability and effectiveness of the proposed ARS approach in the historical traffic state estimation and short-term traffic flow prediction. Complicated traffic states of weaving, merging, and diverging segments can be well distinguished by reconstructing time-space speed diagrams. The proposed approach can be extended to develop efficient missing data imputation algorithms and hierarchical control strategies for heterogeneously congested urban expressways.

Analysis of truck-related crashes of freeways in China

Truck-related crashes result in tremendous lives and property loss and become a serious safety issue in China. The goal of this article is to identify the influential factors for severity of truck-related crashes using data from Jingjintang freeways in China and to design an ordered probit model to explore their relationship. Records including crashes, traffic flow attributes, and geometric design features ranging from 2009 to 2012 were collected from Jingjintang freeway. Crashes are divided into three severity levels: slight injury, injury, and fatal injury. The injury crashes is ranking the first place occupying 64.37%. Truck-related crashes are likely to occur when truck percentage is around 20% and 80%. The speed of traffic flow decreases with the more appearance of trucks. The ordered probit model is developed to estimate the impacts of influential factors on injury severity of truck-related crashes. Marginal effects for each level of injury severity are calculated. The results reveal that truck-involving crashes are highly sensitive to factors such as time of day, truck percentage, average slope, operating speed, speed difference, and exposure variable. The average slope of road segment and speed gaps has the greatest impact on all severity levels of crashes.

Parking policy as an instrument for reducing passenger cars’ harmful emissions

Passenger car related harmful gas emissions have become one of the most significant problems that cities worldwide are facing during the last thirty years. One of the approaches to harmful emissions reduction is certainly preventing or reducing traffic congestion in central urban areas and high trip-attraction zones. One of the congestion influence factors, i.e. (already low) traffic flow speed further reduction, is parking, that is search for a vacant on-street parking space. Since parking search is primarily due to the high occupancy of parking spaces, (better) parking management can affect its reduction. The paper presents the impact of parking time limit and parking price on the passenger cars’ total parking search (cruising for parking) time, as well as their related harmful gases emissions. A survey presented in this paper was carried out in the central urban area of Belgrade, the so-called red parking zone, in order to examine the passenger car users’ preference regarding the parking time limit and parking price variations. The potential benefits in the field of air pollution and fighting climate change due to the implementation of a balanced parking policy and on-street parking price were analysed in this paper.

Travel time prediction with viscoelastic traffic model

Travel time through a ring road with a total length of 80 km has been predicted by a viscoelastic traffic model (VEM), which is developed in analogous to the non-Newtonian fluid flow. The VEM expresses a traffic pressure for the unfree flow case by space headway, ensuring that the pressure can be determined by the assumption that the relevant second critical sound speed is exactly equal to the disturbance propagation speed determined by the free flow speed and the braking distance measured by the average vehicular length. The VEM assumes that the sound speed for the free flow case depends on the traffic density in some specific aspects, which ensures that it is exactly identical to the free flow speed on an empty road. To make a comparison, the open Navier-Stokes type model developed by Zhang (ZHANG, H. M. Driver memory, traffic viscosity and a viscous vehicular traffic flow model. Transp. Res. Part B, 37, 27–41 (2003)) is adopted to predict the travel time through the ring road for providing the counterpart results. When the traffic free flow speed is 80 km/h, the braking distance is supposed to be 45 m, with the jam density uniquely determined by the average length of vehicles l ≈ 5.8 m. To avoid possible singular points in travel time prediction, a distinguishing period for time averaging is pre-assigned to be 7.5 minutes. It is found that the travel time increases monotonically with the initial traffic density on the ring road. Without ramp effects, for the ring road with the initial density less than the second critical density, the travel time can be simply predicted by using the equilibrium speed. However, this simpler approach is unavailable for scenarios over the second critical.

Research of Traffic-Flow Speed on Weaving Sections of Freeway Intersections

Traffic growth on public roads in the Russian Federation requires implementation of new rules and regulations for their design while taking into account heavy traffic flows. Such requirements must be developed on the basis of studies of the traffic flow patterns, including their weaving sections relative to traffic conditions on the country’s road system. The results of traffic flow speeds analyses within the bounds of their weaving sections with regard to the traffic conditions in the Russian Federation have presented in this paper. The observation technique has presented, the obtained results have analyzed and conclusions concerning a significant influence of the weaving sections’ length on traffic speed provided. The conducted research work allows finding a reasonable approach to lengths regulation of the traffic flows weaving sections while considering their speeds.