Traffic Flow Speed Research Articles

MODELLING OF INTERNAL COMBUSTION ENGINES’ EMISSION THROUGH THE USE OF TRAFFIC FLOW MATHEMATICAL MODELS

Road traffic flows on a straight road segment are modelled in this article. The mathematical model of traffic flows has been constructed by using the method of lumped parameters. CO2, CO, CH, NOx, PM regression equations of internal combustion engines’ (ICE) emission has been developed. The accuracy of regression equations is 0.98÷0.99. The article presents assumptions for constructing the mathematical model, description of the mathematical model and gives simulation results. Traffic flow parameters, such as traffic flow concentration and traffic flow speed are presented as modelling results. ICE emission depending on the concentration and traffic flow speed are presented as well.

Research on Relationships among Three Parameters in Short-Term Traffic Flow Forecasting

This paper expects to get the real-time changes of traffic flow by researching the relationships among the three basic parameters flow, speed and occupancy. we firstly carries out the statistical correlation analysis and grey relational analysis to study the connection between the traffic flow parameters flow and speed, flow and occupancy to get a conclusion that there doesn’t exist a significant linear relationship between neither of the comparisons, and the influence of speed on the flow is a little bigger than that of occupancy. Then we try to establish the binary linear regression model without the intercept and GM (0,3) model to do the data fitting, the final simulation results illustrate that the two methods has effects in some extent, also explain the complexity of traffic flow.

Numerical Simulation of Traffic Flow in the Tollgate Area with Variable Speed Limits

We investigate behaviors of vehicles passing a controlled area with variable speed limits (VSL) before a tollgate. The traffic flow mathematical model is formulated based on optimal velocity model. The typical sketch of tollgate area is plotted and variable speed limit signs are set in the area to control the traffic flow speed for fear of accident and congestion. Simulations are carried out to examine the influence on traffic flow passing the controlled area with different number of the speed limit signs under open boundary condition. The simulations results show that more speed limit signs may reduce the risk of rear-end collision and the occurrence of the congestion in the tollgate area.

RESEARCH OF CONGESTIONS IN URBAN TRANSPORT NETWORK USING CELLULAR AUTOMATION MODEL / SPŪSČIŲ MIESTO TRANSPORTO TINKLE TYRIMAS, TAIKANT LĄSTELINIO AUTOMATO MODELĮ / ИССЛЕДОВАНИЕ ПЕРЕГРУЗКИ ГОРОДСКОЙ ТРАНСПОРТНОЙ СЕТИ С ПРИМЕНЕНИЕМ МОДЕЛИ КЛЕТОЧНОГО АВТОМАТ

The growing demand for transport and communication services leads to more and more important, traffic related and closely associated problems, especially in the city centre, such as traffic congestion, air pollution, noise and some others. When modelling traffic flows in the Kaunas city centre, the simulation models of crossroads were created based on the principle of cellular automaton model, taking into consideration such relevant traffic indicators as the average speed of traffic flow in different streets, traffic intensity, congestions and distributed flows. Operation of cellular automaton model is associated with the improved approach of further vehicle model. Modelling of microscopic traffic flows is based on the brake light–cellular automaton (BL–CA) model. Random functions were made discreet and autocorrelation values of these functions were calculated in this work. Fundamental macroscopic traffic characteristics were obtained. Numerical dependences of the average traffic speed and traffic flow, traffic density and traffic flow, the average traffic speed and density were determined, with a help of which the demand parameters of transport network were evaluated in the Kaunas city centre in certain time intervals. Santrauka Didėjantis susisiekimo poreikis lemia vis aktualesnes, ypač centrinėse miestų dalyse, tarpusavyje glaudžiai susijusias eismo problemas: eismo spūstys, oro tarša, triukšmas ir kt. Darbe atliekant transporto srautų Kauno miesto centre modeliavimą, sudaryti ląstelinio automato modelio principu veikiantys imitaciniai sankryžų modeliai, įvertinant tokius eismo požiūriu aktualius rodiklius kaip vidutiniai eismo srauto greičiai skirtingose gatvėse, eismo intensyvumas, eismo spūstis ir srautų pasiskirstymas. Ląstelinio automato modelio veikimas susietas su patobulintu tolesnio automobilio modelio priartėjimu. Mikroskopinis eismo srautų modeliavimas paremtas ląstelinio automato (brake-light, BL-CA) modeliu. Darbe diskretizuotos atsitiktinės funkcijos, apskaičiuotos šiųfunkcijų autokoreliacinės reikšmės. Gautos fundamentalios makroskopinės transporto eismo charakteristikos. Nustatytos vidutinio eismo srauto greičio ir eismo srauto, eismo tankio ir eismo srauto, vidutinio eismo srauto greičio ir tankio skaitinės priklausomybės, kuriomis remiantis įvertinti transporto tinklo paklausos parametrai Kauno miesto centre tam tikrais laiko intervalais. Резюме Возрастающая потребность в перемещении приводит к тесно взаимосвязанным проблемам движения: перегрузке движения (заторам), шуму, загрязнению среды и т. д., что проявляется и особенно актуально в центральных частях города. В статье исследуются транспортные потоки в центре города Каунаса (Литва). С использованием принципа модели клеточного автомата (клеточный автомат – это математический объект с дискретными пространством и временем, каждое положение в пространстве представлено отдельной клеткой) созданы действующие имитационные модели перекрестков, учитывающие актуальные с точки зрения движения показатели: среднюю скорость потока движения на различных улицах, интенсивность движения, перегрузку потока и распределенный поток. Работа модели клеточного автомата связана с усовершенствованной моделью приближения следующего автомобиля. Микроскопическое моделирование потоков движения основано на модели клеточного автомата (brake-light, BL-CA). В работе дискретизированы случайные функции, вычислены значения автокорреляции этих функций, получены фундаментальные макроскопические характеристики транспортного движения, установлены числовые зависимости средней скорости потока движения и потока движения, транспортной плотности и потока движения, средней скорости движения и плотности, с помощью которых оценены параметры потребности транспортной сети в центре Каунаса с определенными временными интервалами.

Highway Capacity Prediction in Adverse Weather

The purpose of this study was to find out the effects of rainfall on traffic flow rates and the implications on highway capacities. Data was generated from a pneumatic tube detector placed on a 2 km straight section of a principal road that was operating in the free flow regime. This is with a view to isolating all bottlenecks and incidences that could affect traffic flows and to see the direct effect of the rainfall on traffic. Data from nearby rain gauge station was used to identify dry and wet traffic flow conditions. Empirical evidence exists for traffic flow contraction, speed reduction and increase in density. A speed reduction of 3.52% resulted in a flow rate change of 8.64% under rainfall conditions. Furthermore, the fundamental diagram was used to predict the capacity flows in both dry and wet conditions. A 42.27% loss of capacity was obtained at critical densities of 186.82 and 111.97 vehs km -1 for both dry and wet conditions respectively. It is concluded that adverse weather can seriously degrade the capacities of highways. At higher flow rates, the instabilities that could result from adverse weather effects can cause prolong delays to drivers with its attendant economic losses. Rainfall intensity variation should be investigated to determine capacity loss thresholds at which resources can be placed to manage traffic in adverse weather.

The Relationship between Ramp Length and Traffic Flow Speed (TFS) for Interchange

The relationship between ramp length and traffic flow speed (TFS) was studied based on analyzing the design elements of geometry alignment for interchange. After analyzing the process of vehicle running in the ramp, the speed change process was divided into four forms, namely, one deceleration and acceleration process, one deceleration process, one acceleration process and more than one deceleration and acceleration process, and then the relationship between the ramp length and TFS was established respectively. Through an example of the HeDa Interchange of Heilongjiang Province, it showed that although the differences of alignment units of ramps can result in various speeds and specific expressions of relationship between ramp length and TFS. However, all of these relations can be expressed by homologous nonlinear function.

Optimal Measurement Interval for Pedestrian Traffic Flow Modeling

Measurement interval is crucial in obtaining stable traffic flow parameters, such as traffic flow rate, density, and speed. Credible relationships among these parameters and reasonable capacity for analysis are also dependent on the appropriate measurement interval. Nevertheless, the measurement interval has not been mentioned explicitly in most previous studies related to pedestrian traffic flow. Different researchers adopted various time intervals for traffic flow parameters measurement, and the reasons for the choice of a certain measurement interval were usually not clearly stated. This paper deals with the impact of different intervals on the results of pedestrian traffic flow parameters counting and the methods to determine the appropriate measurement interval. It takes pedestrian traffic in Shanghai Metro stations into an observation context. By video recording, pedestrian traffic parameters, including volume and density, are extracted manually through recording tapes using an initial 5-s interval for level passageway, ascending stairway, descending stairway, and two-way stairway. Taking 5 s as the basic incremental unit, traffic parameters for 10-s interval, 15-s interval, and other analogical time interval values are acquired in sequence. On the basis of the principles of measurement interval selection, the appropriate measurement interval is determined by comparing its influence on stability of hourly flow rate and invariability of pedestrian traffic status when applying different time interval values. It is revealed that a 30-s interval value is optimal for all the observed facilities in this research context. From the analysis of optimal measurement interval, it could also be inferred that traffic stability of level passageway is higher than that of stairways, and a one-way stairway is more stable than a two-way stairway. The collected data, proposed methods, and revealed pedestrian flow characteristics could be helpful in improving the theories on pedestrian traffic flow, and serve as valuable references for similar pedestrian context studies. Language: en

Empirical Study of Driver Responses during the Yellow Signal Phase at Six Maryland Intersections

This paper presents the analysis results of driver responses during a yellow phase, based on field observations of 1,123 drivers collected with a specially designed system from six signalized intersections of high crash frequency in Maryland. By classifying drivers into aggressive, conservative, and normal groups based on their responses (i.e., stop or pass) and the distances to the stop line when the signal turns yellow, the statistical tests with the ordered probit model clearly indicate some critical variables and their impacts on a driver’s decision at intersections. Such variables include average traffic flow speeds, traffic volume rate, the green split, the number of through and crossing lanes in the target approach, signal coordination, the difference between a vehicle’s approaching speed and the average traffic flow speeds, a driver’s gender and age, talking over a cell phone or not, a vehicle’s type and model, and so on. The research findings for this study offer the basis for responsible agencies to identify underlying factors contributing to aggressive maneuvers at signalized intersections which often cause traffic crashes, and to develop improvement strategies, such as customized driver education and intelligent safety protection systems.

Estimation of Day-Evening-Night Sound Level of Road Traffic Noise in Urban Area

Road traffic noise, within an urban area, is under consideration. The proposed method enables approximation of the yearly average value of the day-night sound level, L den , and its uncertainty, U den . The method requires measurements of the one-hour average sound level, L Aeq,1h , and concurrent measurements of the hourly traffic flow and traffic speed. The measurements have to be carried out under four types of meteorological conditions. Calculations of L den and U den are facilitated by the use of the Japanese model of noise generation.

Empirical Study on Relationship among the Lane-Changing, Speed and Traffic Flow

Lane-changing behavior in weaving segment of urban expressway in transportation engineering is a significant factor contributing to the loss of capacity. This paper attempts to analyze the statistical relationships among lane-changing, speed and density of traffic flow in different lanes of weaving segment of urban expressway under a given traffic condition and general levels of service. Based on the analysis result, a series of models is recommended. The effectiveness between the recommended models and the existing model is compared. Although the optimization effect not very clear, but the lane-changing factors have some relationship with the traffic characteristics in weaving segment of urban expressway.

Evaluation of Effectiveness of Coordinated Signal Control in Reducing Vehicle Emissions during Peak Hours versus Nonpeak Hours

Traffic signal coordination is not only an effective traffic flow operational strategy to smooth the traffic in urban areas but is also considered a potentially effective means to reduce vehicle emissions. Nevertheless, when traffic flow speed decreases, the effectiveness of using traffic signal coordination to reduce emissions may be substantially weakened. This paper evaluates the effectiveness of signal coordination in reducing vehicle emissions during peak versus nonpeak hours, two speed scenarios. The operating mode binning approach is used as a statistical technique to calculate emission rates, and the difference in emissions is adopted as the measure of effectiveness in the study. Data used in the study include Global Positioning System data and emission data collected from real-world tests. It was found from the study that coordinated signal control could reduce vehicle emissions in the following order (most to least reduction): oxides of nitrogen, carbon dioxide, hydrocarbons, and carbon monoxide. However, its effectiveness would be impaired during peak hours when the speed was decreased. Meanwhile, the test shows that the effectiveness will be affected by driver behavior. Either low average speed or intentionally slow driving will weaken the effectiveness of coordinated control in reducing vehicle emissions. The research in this paper is a pilot study and the same methodology will be used to conduct a more thorough study.

Speed Estimation from Single Loop Data Using an Unscented Particle Filter

Abstract: This article presents a hybrid method, the Unscented Particle Filter (UPF), for traffic flow speed estimation using single loop outputs. The Kalman filters used in past speed estimation studies employ a Gaussian assumption that is hardly satisfied. The hybrid method that combines a parametric filter (Unscented Kalman Filter) and a nonparametric filter (Particle Filter) is thus proposed to overcome the limitations of the existing methods. To illustrate the advantage of the proposed approach, two data sets collected from field detectors along with a simulated data set are utilized for performance evaluation and comparison with the Extended Kalman Filter and the Unscented Kalman Filter. It is found that the proposed method outperforms the evaluated Kalman filter methods. The UPF method produces accurate speed estimation even for congested flow conditions in which many other methods have significant accuracy problems.

Calculation of traffic flow breakdown probability to optimize link throughput

Traffic breakdown phenomenon is prevalent in empirical traffic system observations. Traffic flow breakdown is usually defined as an amount of sudden drop in traffic flow speed when traffic demand exceeds capacity. Modeling and calculating traffic flow breakdown probability remains an important issue when analyzing the stability and reliability of transportation system. The breakdown mechanism is still mysterious to practitioners and researchers in varying manner. Treating breakdown as a random event, this paper use discrete time Markov chain (DTMC) to model traffic state transition path, as a result, a transition probability matrix can be generated from empirical observations. From empirical analysis of breakdown, we found this formulation of breakdown probability follows the Zipf distribution. Therefore, a connection from traffic flow breakdown probability to how many vehicles are occupying a certain freeway segment (e.g. a link) will be established. Following from the results, a quantitative measure of breakdown probability can be obtained to optimize ramp metering rates to achieve optimum system performance measures.

Roundabouts in Signalized Corridors

Typically, roundabouts in the United States are installed at isolated intersections to address location-specific safety or operational needs. The use of roundabouts in signalized corridors, however, has not been well evaluated. It is commonly believed that roundabouts can improve traffic flow and travel speeds along an urban corridor by reducing delay caused by idling at intersections. Concern exists, however, that a roundabout in a coordinated signalized corridor will disrupt continuous traffic flow: downstream signals can more efficiently process vehicles in a platoon, and roundabouts disperse rather than form platoons. Roundabouts also can discharge vehicles more efficiently when traffic arrives randomly. Thus unnecessary queuing may result when roundabouts are downstream of signalized intersections. Since little research was available to compare the traffic flow impacts of roundabouts within a signalized corridor, two case studies were evaluated with the microscopic traffic simulation package, VISSIM. A roundabout and two signalized alternatives, as well as a roundabout and a four-way, stop-controlled alternative, were compared at intersections along signalized corridors in Ames, Iowa, and Woodbury, Minnesota, respectively. The traffic data and corridor geometry were coded into VISSIM, and traditional intersection traffic control within the corridors was compared with a scenario that had a two-lane roundabout. With the microsimulation software, average travel time, stopped delay, and average delay for the entire corridor were compared.

MATHEMATICAL MODELLING OF NETWORK TRAFFIC FLOW

The article describes mathematical models of traffic flows to initiate different traffic flow processes. Separate elements of traffic flow models are made in a way to be connected together to get a single complex model. A model of straight road with different boundary conditions is presented as a separate part of the network traffic flow model. First testing is conducted in case the final point of the whole modelled traffic line is closed and no output from that point is possible. The second test is performed when a constant value of traffic flow speed and traffic flow rate is entered. Mathematical simulation is carried out and the obtained results are listed.

Cellular automaton model for mixing traffic in two-lane system with period boundary condition

Based on the analysis of the existing classical cellular automaton model of traffic flow, considering the characteristic of part of expressways without differences between running lane and passing lane, we demarcated the parameters such as length of the cellar automaton, operation speed, random slow mechanism and the max speed etc, set up the vehicle's generating function and vehicle changing lane regulation, and established Cellular Automaton (CA) model for mixing traffic in two-lane system with period boundary condition. Then we analyzed the relation among three parameters of traffic flow through computer simulation, and the impact of the occupation rate of large-scale freight vehicles on traffic flow. We compared the space-time evolution figure with density changing under the same occupation of large-scale vehicles. The result shows that the occupation rate of large-scale freight vehicles has little influence on the speed of mixed traffic flow in the situation that the expressways have no differences between running ways and passing ways. The stochastic deceleration probability of the vehicle plays an important role in the motion state of mixed traffic flow.

Influence of Various Restrictions on Speed–Flow Models

This paper presents traffic speed models developed on the basis of numerous measurements. In studies of the speed–flow relationships the following research issues were analyzed: impacts of the speed limit, traffic flow, traffic flow composition, and time of day on speed–flow and impacts of qualitative road and roadside features (cross sections, road function, accessibility, intensity of development, roadside pedestrian traffic) on free-flow speed. The research included road sections with numerous constraints of traffic freedom. Such sections include sections of roads through built-up areas (small communities and towns). Regression analysis using generalized multiple regression was the basic tool in investigations. In addition, in analyzing data from speed measurements, the classic form of the logit function for a multiple-valued regression was applied. The analyses showed that even at general and posted speed limits the characteristic traffic flow–speed relations can be identified. The shape of these relations is characteristic of empirical results in which the spread of recorded values is typical for randomness and impacts of local factors. Average speed in traffic flow depends not only on geometric alignment of a road cross section but also on local factors and speed limits. Speed in free-flow traffic is significantly influenced by qualitative road and roadside characteristics. Most important of these factors are type of cross section, intensity of roadside development, and accessibility of the road.

Estimation of Traffic Density on Urban Freeways

Traffic density is one of the most important parameters to identify traffic state, but it is very difficult to be acquired in real world. This paper has proposed a method to estimate traffic density using the output (traffic flow and time mean speed) of fixed traffic detectors. The method firstly converts time mean speed to space mean speed by introducing the coefficient of variation and standard error of space speed, and then, acquires traffic density through the relationship between traffic flow, density, and space mean speed in traffic flow theory. Furthermore, the paper has indicated that traffic density is insensitive to the coefficient of variation of space speed. In the end, the method has been applied to Shanghai inner elevated ring freeway and the traffic density can be reasonably estimated. In addition, fitting curves among traffic flow, density, and space mean speed are acquired. The results are similar to classic traffic flow theory. The method can estimate traffic density directly on the basis of outputs of fixed detectors, especially for urban freeways with lots of traffic detectors, which are laid with mutually short distance. It is proved that the method is very simple and applicable to urban freeways.

Optimal Total Vehicle Pollutants Emission Quantity Based on Link Traffic Capacity Constraints

With the growing of vehicles ownership, the vehicular exhaust emissions have become major sources of air pollution in cities. In this paper, the pollutants, carbon monoxide (CO), nitrogen oxides (NO x), and hydrocarbon (HC) are considered as evaluation factors. On the basis of the relation between the emission factors and vehicle's velocity and the relation amongst three parameters (Volume, Speed, and Density) of traffic flow, we have designed a model. This calculates the total quantity of pollutants emission from vehicles based on speed, proportion of vehicle types, and traffic volume. Using the theory of nonlinear programming, we have formed an optimal model in which the link capacity is one main constraint and the minimum of the total quantity of pollutants emission is the goal and designed its algorithm solution. The aim of our research is to find a method to control the quantity of traffic pollutants emission through adjusting and controlling the composition of vehicle types, and then the traffic volume and vehicle's running speed indirectly. Finally, the feasibility of the model is justified through a practical example.

Road Capacity and Performance Implications of Ramp Closure Toronto, Canada, Experience

To alleviate traffic congestion and safety concerns on the Gardiner Expressway in Toronto, Ontario, Canada, the City of Toronto has elected to implement scheduled closures for the two on-ramps since early 1970s. This study investigates the traffic impacts of the daily on-ramp closures at Gardiner Expressway and Jameson Avenue. The average changes to traffic flow variables such as traffic volume throughput due to the ramp closures are computed quantitatively. Results show that ramp closure has resulted in smoother traffic flow and higher travel speed but not higher traffic throughput on the expressway. Ramp reopening causes a spike in speed variations as measured by upstream detectors. The network performance metrics (vehicle hours traveled, vehicle kilometers traveled, delay, and travel time) are computed and analyzed to determine the performance benefits of the ramp closures. The travel time saving in the area due to the ramp closure is estimated to be 225 vehicle-hours per day.