Saturation Flow Rate Research Articles

Determining the appropriate lane width at urban signalised intersections – a case study in Beijing

Intersections are the key nodes in an urban traffic network that affect overall traffic efficiency. Lane width is a major element of an intersection that is affected by the saturation flow rate of the intersection. It is also influenced by a variety of other factors, such as road resource constraints, vehicle composition, traffic safety, and driving comfort. To determine the appropriate lane width, this study analysed relationships between lane widths and design-related factors, including saturation flow rate, lateral safety distance, traffic crash rate, and driver comfort. First, screening and surveys were conducted using the design data of more than 3000 existing crossroads. Then, seven intersections with different lane widths were selected. To collect traffic flow data, video-based surveys were conducted. Meanwhile, the traffic crash rate was collected to assess traffic safety. Moreover, surveys were conducted to assess the driving experience. Finally, the Delphi method was developed to evaluate the index weights of the design-related factors. The case study revealed that the optimal lane width for four-legged intersections is 3.1 m. A lane width of 2.8 m is an alternative for cases of limited road resources. The results could be supplementary guidance or reference for road designers and administrators.

Traffic Evaluation of SPUI and TUDI Interchanges Based on Traffic Conditions in Tehran with Aimsun and Synchro Software

There are various interchanges with specific features and applications. The single-point urban interchange (SPUI) and tight urban diamond interchange (TUDI) are diamond and used in areas with limited right of way, and they have not been used in Iran so far. The choice between these two very similar interchanges is challenging. It is difficult for transportation engineers to choose between them without being aware of their right performance. This study aimed at measuring the efficiency of these interchanges using five measures of effectiveness for having more efficient interchanges in specific traffic conditions. The Synchro 9, Sim Traffic 9 and AIMSUN 6 software and calibrated values have been used for simulation for Tehran. Parameters such as vehicle specifications, give way time, lost time and saturation flow rates were calibrated using the calibration values based on the conditions in Tehran. The traffic data of NCHRP 3-60 report were used. Twelve different traffic scenarios which are covering different volumes were used for simulation. First, the least time of scenario cycle was calculated using Webster’s formula, and then, each scenario phase was optimized using Synchro software, and optimized scenarios were simulated using AIMSUN software. The results indicated that the SPUI interchange had lower delay, stop time, travel time and density while its average speed was higher. In general, by increasing traffic volume, the performance differences increase between the SPUI and TUDI interchanges in different parameters.

The influence of gradient on saturation flow rate at signalised intersections

Saturation flow rate is the maximum hourly traffic volume per lane that can be accommodated through an intersection, and is used in the design and analysis of signalised intersections and traffic signal plans. The most widely applied method to estimate saturation flow rate is provided by the Highway Capacity Manual (HCM), which proposes default values obtained from USA empirical data for application in saturation flow rate calculations. This study considers the applicability of the HCM proposed base saturation flow rates, and particularly the adjustment factors for gradient on saturation flow in the South African context. The data for this research was collected by author ES Viljoen for use in her dissertation conducted in the final year of the BEng degree at Stellenbosch University. The influence of approach lane gradient on saturation flow rate was investigated for application in the South African environment. The results of this research indicate that the HCM underestimates the influence of approach gradient on saturation flow rate, a similar finding to other international research. The standard use of a base saturation flow rate of 1 900 passenger cars per hour per lane for South African conditions was also commented on. HCM methods do not take into account the influence of speed limit on saturation flow rate, which has been shown to significantly affect saturation flow rate in numerous research projects, and is also commented on in this paper for zones with a 60 km/h and 80 km/h speed limit.

Trajectory-Based Measurement of Signalized Intersection Capacity

Capacities of road intersections are a limiting factor and crucial for the performance of road networks. Therefore, for purposes of intersection design and of optimal signal timing, numerous methodologies have been proposed to either estimate or directly measure the capacity of single movements at road intersections. However, both model-based estimation and direct measurement suffer from the large effort that is needed to gather the relevant data. Even worse, once the data are collected they only represent a snapshot of the capacity over time. This paper proposes an alternative approach to estimate capacity of signalized road intersections over time using only automatically generated trajectories of probe vehicles. The obtained capacity can be used to evaluate the effective degree of saturation using real demand, or to assess hypothetic different conditions in demand or signaling. The cyclic operation of signalized intersections allows for the accumulation of trajectories, and thus in practical applications for the compensation of potentially low penetration rates. Within a sequential process the intersection’s cycle time and the approach green time and saturation flow rates are determined. The determination of the cycle time and the green times is based on an existing approach. The derivation of the saturation flow rates relies on its direct dependency to the saturation time headway and uses two parameters to be calibrated. Testing with a commercial dataset on an intersection in Munich produced a good signal timing estimation and saturation flow values that are comparable to a calculation based on the German guideline.

Steady-State Car-Following Time Gaps: An Empirical Study Using Naturalistic Driving Data

The time gap is defined as the time difference between the rear of a vehicle and the front of its follower, which affects both safety and the saturation flow rate of a roadway segment. In this study, naturalistic driving data were examined to measure time gaps from seven different drivers in a car-following scenario within steady-state conditions. The measurements were taken from a 13-km section of a Dulles Airport access road in Washington, DC. In total, 168,053 time gap samples were obtained covering seven speed intervals. Analysis of the data revealed a large variation in time gaps within individual drivers’ driving data, with coefficients of variation as high as 63.8% observed for some drivers. Results also showed that the variability within drivers was more significant at speeds higher than 54 km/h. In addition, there was a large variability between drivers. At speeds above 108 km/h, minimum time gaps left by some drivers could be 1.6 times longer than those left by others. Several statistical distributions were used to fit the data of the seven drivers as well as the data for all drivers combined for each speed interval. The selected distributions passed the goodness-of-fit (Kolmogorov-Smirnov, Chi-square, and Anderson-Darling) criteria only when the number of samples was reduced. Data reduction was not performed randomly, but rather in a manner intended to maintain the same observed distribution when all the samples were used. It is therefore recommended that empirical measures of distributions be used in traffic microsimulation software rather than theoretically fit distributions obtained based on statistical tests. This will lead to better naturalistic traffic behavior simulations, resulting in more precise predicted measures of performance (travel time, fuel consumption, and gas emissions).

Impact of Guideline Markings on Saturation Flow Rate at Signalized Intersections

Many intersections around the world are irregular crossings where the approach and exit lanes are offset or the two roads cross at oblique angles. These irregular intersections often confuse drivers and greatly affect operational efficiency. Although guideline markings are recommended in many design manuals and codes on traffic signs and markings to address these problems, the effectiveness and application conditions are ambiguous. The research goal was to analyze the impact of guideline markings on the saturation flow rate at signalized intersections. An adjustment estimation model was established based on field data collected at 33 intersections in Shanghai, China. The proposed model was validated using a before–after case study. The underlying reasons for the impact of intersection guideline markings on the saturation flow rate are discussed. The results reveal that the improvement in the saturation flow rate obtained from painting guide line markings is positively correlated with the number of traffic lanes, offset of through movement, and turning angle of left-turns. On average, improvements of 7.0% and 10.3% can be obtained for through and left-turn movements, respectively.

Effects of winter weather on traffic operations and optimization of signalized intersections

Abstract Adverse winter weather has always been a cause of traffic congestion and road collisions. To mitigate the negative impacts of winter weather, transportation agencies are under increasing pressure to introduce weather responsive traffic management strategies. Currently, most traffic signal control systems are designed for normal weather conditions and are therefore suboptimal regarding efficiency and safety for controlling traffic during winter snow events due to changes in traffic patterns and driver behaviors. The main objective of this research is to explore how to modify pre-timed traffic signal control parameters under adverse weather conditions to increase traffic efficiency and road safety. This research consists of two main components. First, we examine the impacts of winter weather on three key traffic parameters, i.e., saturation flow rate, start-up lost time, and free flow speed. Secondly, we investigate the potential benefits of implementing weather-specific signal control plans for uncoordinated intersections as well as coordinated corridors. Two case studies are conducted, each with varying levels of traffic demand and winter event severity, to compare the performance of different signal plans. Evaluation results from both Synchro and VISSIM show that implementing such signal plans is most beneficial for intersection with a medium level of traffic demand. It is also found that the benefit of implementing weather-responsive plans was more compelling at a coordinated-corridor level than at an uncoordinated-intersection level.

Optimal location of the U‐turn at a signalised intersection with double left‐turn lanes

The location of the U-turn median opening at signalised intersections can have important effects on the intersection performance. However, there has been very little prior work on this issue, especially on intersections with double left-turn lanes. This study analyses the mutual interference of the U-turn and the left-turn movements at signalised intersections with double left-turn lanes. A lane selection model, based on the Wardrop Equilibrium Principles is developed for left-turn drivers. The saturation flow rate model of the double left-turn lanes is developed to quantitatively evaluate its utilisation. This study also presents the guidelines for the design of the U-turn median opening for maximising the saturation flow rate of double left-turn lanes. The proposed model is also verified by means of simulation, and then a case study is used to compare the intersection performance before and after optimisation. The results of case study show that if the U-turn locations are varied, the saturation flow rate of the double left-turn lanes would also vary considerably. The authors show that there can be a major difference of 77.47%, and the saturation flow rate of optimal location can be improved by 7.63% compared with the current location of the U-turn median opening.

Coupling of CFD and population balance modelling for a continuously seeded helical tubular crystallizer

A comprehensive model coupling the computational fluid dynamics with the population balance equation (CFD−PBE) for a continuous seeded mixed suspension mixed product removal (MSMPR)-helical tubular (HT) crystallizer assembly has been developed. The model accurately depicts the fluid dynamics, mass transfer, heat transfer and crystal size distribution (CSD) in the MSMPR-HT crystallizer. The crystallization system considered was to produce metastable α-form of L-glutamic acid. The PBE was discretized using a high-resolution central scheme and solved simultaneously with CFD equations in COMSOL Multiphysics® utilizing user-defined scalars. A good agreement was observed between the model and experimental data for the metastable α-form crystals of L-glutamic acid with uniform particles and a mean crystal size of 160 µm. The continuous crystallization under different stirrer speeds, saturated solution flow rates, inlet saturated solution concentrations and temperature was investigated. It was found the higher stirrer speeds, saturated solution flow rate and temperature lead to uniform distribution with smaller crystal size. Moreover, the mean crystal size becomes larger and the CSD wider when the saturated solution concentration increase.

Single capillary oximetry and tissue ultrastructural sensing by dual-band dual-scan inverse spectroscopic optical coherence tomography

Measuring capillary oxygenation and the surrounding ultrastructure can allow one to monitor a microvascular niche and better understand crucial biological mechanisms. However, capillary oximetry and pericapillary ultrastructure are challenging to measure in vivo. Here we demonstrate a novel optical imaging system, dual-band dual-scan inverse spectroscopic optical coherence tomography (D2-ISOCT), that, for the first time, can simultaneously obtain the following metrics in vivo using endogenous contrast: (1) capillary-level oxygen saturation and arteriolar-level blood flow rates, oxygen delivery rates, and oxygen metabolic rates; (2) spatial characteristics of tissue structures at length scales down to 30 nm; and (3) morphological images up to 2 mm in depth. To illustrate the capabilities of D2-ISOCT, we monitored alterations to capillaries and the surrounding pericapillary tissue (tissue between the capillaries) in the healing response of a mouse ear wound model. The obtained microvascular and ultrastructural metrics corroborated well with each other, showing the promise of D2-ISOCT for becoming a powerful new non-invasive imaging tool.

Determination of Adjustment Factors for Far Side and Near Side Bus Stops on Saturation Flow

Saturation flow under mixed traffic conditions is affected by vehicular mix and its characteristics, approach grade, driver behaviour, roadway geometry, and road side frictions in the vicinity of intersection. Side friction arises from pedestrian movement, activities of public transport vehicles, and parking of vehicles on road premises. Due to the influence of these factors, realistic estimation of saturation flow is a complex task under heterogeneous traffic conditions. Road side friction arising from stopping of public transport adjacent to signalised intersection tends to interfere with vehicular discharge at intersections. This paper attempts to analyse the impact of far side (down stream side) and near side (upstream side) bus stops on saturation flow rate. As a first step towards quantifying the effect of bus stops, saturation flow of approaches that satisfies the base conditions set for the study were estimated in PCU/hr using area occupancy concept. Mathematical model for the prediction of base saturation flow was proposed. Effect of bus stops on saturation flow rate was then determined by analysing saturation flow rates of approaches where bus stops are located adjacent to intersections. Adjustment factors were introduced to incorporate the effect of far side bus stop (Ffb) and near side bus stop (Fnb) on saturation flow rate. Linear regression models were developed for the prediction of adjustment factors based on data generated using a micro simulation programme. The results of the study showed that adjustment factors vary with distance of bus stop from stop line, width of approach and proportion of green time blocked. The study also revealed that the reduction in saturation flow rate is more when bus stops are located in the upstream side (near side bus stop).

Automatic Estimation Method for Intersection Saturation Flow Rate Based on Video Detector Data

Saturation flow rate (SFR) is a fundamental parameter to the level of service evaluation, lane capacity calculation, and signal timing plan optimization at signalized intersections. It is affected by a variety of factors including weather conditions, lane width, and the type of the driver. How to accurately estimate the SFR remains one of the most important tasks in traffic engineering. Existing studies generally rely on the field measurement method which requires a large number of people collecting data at the intersection. As a result, the method incurs a high economic cost and cannot adapt to the dynamic change of SFR. In recent years, video detectors have been widely installed at intersections which are capable of recording the time each vehicle passes the stop line, the number plate of each vehicle, and the vehicle type. This paper therefore aims to propose an automatic estimation method for the SFR based on video detector data in order to overcome the limitation of the field measurement method. A prerequisite for estimating the SFR is to recognize the saturation headway. We consider the actual vehicle headway as time series and build an auxiliary regression equation whose parameters are estimated through the ordinary least squares method. We employ the Dickey-Fuller test to verify whether the headways in the time series are saturation headways. An iterative method using quantiles is proposed to filter out abnormal data. The SFR is finally calculated using the average value of saturation headways. To demonstrate the proposed method, we conduct a case study using data from an intersection with three entrance lanes in Qujing city, Yunnan Province, China. The overall estimation process is displayed and the impacts of quantile selection and data duration on the estimation accuracy are analyzed.

Estimating saturation flow under weak discipline traffic conditions, case study: Iran

Intersections, as the critical elements and the major bottleneck points of urban street networks, may have inconsistent performances in different countries. This is largely due to the fact that the factors affecting their performance e.g. driving behavior, vehicle characteristics, control methods, and environmental conditions may vary from one country to another. It is, therefore required to take into account these factors when developing or applying available models and methodologies for their capacity analysis or signal control setting. This is particularly important for the countries with heterogeneous and weak discipline traffic streams such as Iran. Meanwhile, estimating the saturation flow rate, which is a key parameter in capacity and delay analysis and in optimal timing of traffic signals, is of great importance. In this study, the possibility of identifying and or developing appropriate models for estimating the saturation flow rate at the signalized intersections in these situations has been explored. For this purpose, a case study performed at the signalized intersections located in the city of Yazd, a medium sized city located in the middle of Iran. Using the data obtained from several intersections together with the application of analytical procedures proposed by American, Australian, Canadian, Indonesian, Iranian and Malaysian highway capacity guides, the saturation flow rate was estimated from both field observations and analytical methods. A comparison of these results indicated that in the protected left-turn situations, the Australian guide produced the best comparable results with the field data. On the other hand, in the permitted left-turn situations, the method proposed in the American Highway Capacity Manual guide produced the best comparable results with the field data. Furthermore, three new models were developed for estimating the saturation flow rate in three different situations namely, unopposed mixed straight and turning traffic movements, opposed mixed straight and turning traffic movements and merely straight through movement. The effective width, traffic composition, and opposite oncoming through traffic flow were considered as the effective parameters in the proposed models. Moreover, using the multivariate regression analysis, the Passenger Car Equivalent coefficients for motorcycles and heavy vehicles were calculated as 0.51 and 2.09, respectively.

Impact Assessment of Short-Term Work Zones on Intersection Capacity in New York City

New York City infrastructure is one of the oldest transportation infrastructures in the United States. Local street construction and short-term work zones are almost continuously planned events that affect the movement of traffic on city streets by requiring the closing of one or more lanes at intersections throughout NYC, and it is important to understand the effect on capacity due to such work. This paper looks at the effect of short-term work zones on the capacity of signalized intersections in New York City. Data was collected at five locations in New York City, both during the work zone and then again after the work zone was removed. Over 25 hours of video data was collected and reduced. It was found that at all locations, the saturation headway was smaller during the work zone compared to after the work zone was removed, that is, the saturation flow rate per lane increased during the work zone. This was an unexpected result. A possible reason for this is the increased traffic pressure that drivers feel when a lane is closed. Thus, although overall approach capacity does decrease because a lane is closed, it did not decrease as much as expected. The field values are then compared with those from two other models: the Highway Capacity Manual model and a model developed by Schroeder et al. It was found that both models underestimate the capacity of the approach.

ESTIMATION OF FACTORS AFFECTING BASE SATURATION FLOW RATE AT SIGNALIZED INTERSECTION

With growing population and urbanization to provide the safe and efficient traffic is a challenging task to the transportation engineering. To estimate the traffic at signalized / un-signalized intersection the base saturation flow rate play vital role. The base saturation flow rate was measured and analyzed to provide the smooth traffic flow rate at Hyderabad, for four intersection approaches. The objective of the study is to estimate and develop the affecting parameter of base saturation flow rate for various approaches in the Hyderabad city. Form the obtained base saturation flow rate, the capacity of the signalized intersection was determined. The study result was concluded that the maximum base saturation flow rate found at L. B nagar and also the minimum base saturation flow rate at tarnaka. It’s also indicated that the parameter affects the base saturation flow rate at various approaches and its factors values were described.

The impact of highway base-saturation flow rate adjustment on Kuwait's transport and environmental parameters estimation

Traditional transportation systems' management and operation mainly focused on improving traffic mobility and safety without imposing any environmental concerns. Transportation and environmental issues are interrelated and affected by the same parameters especially at signalized intersections. Additionally, traffic congestion at signalized intersections has a major contribution in the environmental problem as related to vehicle emission, fuel consumption, and delay. Therefore, signalized intersections' design and operation is an important parameter to minimize the impact on the environment. The design and operation of signalized intersections are highly dependent on the base saturation flow rate (BSFR). Highway Capacity Manual (HCM) uses a base-saturation flow rate of 1900-passenger car/h/lane for areas with a population intensity greater than or equal to 250,000 and a value of 1750-passenger car/h/lane for less populated areas. The base-saturation flow rate value in HCM is derived from a field data collected in developed countries. The adopted value in Kuwait is 1800passengercar/h/lane, which is the value that used in this analysis as a basis for comparison. Due to the difference in behavior between drivers in developed countries and their fellows in Kuwait, an adjustment was made to the base-saturation flow rate to represent Kuwait's traffic and environmental conditions. The reduction in fuel consumption and vehicles' emission after modifying the base-saturation flow rate (BSFR increased by 12.45%) was about 34% on average. Direct field measurements of the saturation flow rate were used while using the air quality mobile lab to calculate emissions' rates.

Analysis of saturation flow rate at tandem intersections using field data

A tandem intersection is an unconventional intersection design that possesses the important property of increasing the traffic capacity using pre-signals and sorting areas. However, the operational efficiency of the lanes in the sorting areas may be affected by driver unfamiliarity and confusion. This study evaluates the effect of the tandem control on the saturation flow rate using field data. Statistical analyses were conducted to identify the difference in the saturation flow rate of the approach lanes when the tandem control was open and closed. A saturation flow rate adjustment model for tandem control was established in accordance with three factors: unequal distribution of traffic, red light violations at the pre-signal, and incomplete discharge of vehicles at the sorting area. The results indicate that the tandem control decreases the saturation flow rate of the approach lanes in the sorting area. Most of the observed reductions are caused by the first factor, i.e. the unequal distribution of traffic. The other two factors, red light violations and incomplete discharge, can be controlled by using appropriate traffic signs, markings, and signal timing design.

IMPACT OF GEOMETRY AND TRAFFIC CHARACTERISTICS ON SATURATION FLOW RATES AT SIGNALIZED INTERSECTIONS

Signalized intersections play a critical role in the motion of both urban and arterial streets. One of the basic parameters for the design and analysis of signal controlled intersections is saturation flow rate. This paper reports the estimation of saturation flow rate (SFR) considering the prevailing conditions in Egypt, at signalized intersections. Accordingly, three main objectives are stated for this study: The first one is to investigate the effect of the geometric and traffic characteristics on saturation flow rates. The second objective is to estimate a calibration factor for using US-HCM-2010 model to be suitable for the prevailing conditions in Egypt. The third objective is to develop a regression model for SFR considering intersection characteristics in Egypt.The required data for this study was collected at four signalized intersections in Shebin-Elkom city and in Tanta city using video recording technique. Geometric data and signal data were collected manually in the field. Data analysis showed that with the increase of the lane width, the saturation flow rate increases. The same conclusion can be extended to the turn-radius and vice versa with HV%. While comparing the saturation flow calculated from US-HCM-2010 with measured saturation flows, it is observed that the values aren't matching with the difference in values as 7.6%. After calibration, it can be seen that calibrated saturation flow based on US-HCM-2010 model is closer to the measured saturation flow with difference of 2.1%. Many regression models were developed for saturation flow rate considering intersection characteristics in Egypt. The best model has R2 equals 78%. This models includes 3 independent variables; %HV, lane width and lane type. The results indicated that, SFR measured using this model is closer to the field measured with a maximum difference of 1.2%. The model is valid for estimating the saturation flow rate at signalized intersections in Delta region of Egypt that have similar characteristics.

Study of the impact of type and condition of the road surface on parameters of signalized intersection

Abstract This paper explores the effects of the road surface type and condition on the traffic flows management mode in case of directive management. The subject matter of the study is the process of traffic flow movement at a signalized intersection. The scope of the study is the method of assessment of effect of the road surface type and condition on the capacity rate of the signalized area and therefore its effects on the traffic flow management mode. Building on the existing scientific data, the authoring team carried out studies in the area of signal control and determined a number of parameters that have an effect on traffic management modes in urban environment. The analysis of papers on the saturation flow value that is used to calculate the parameters of a signalized intersection and experimental findings showed that this value is influenced by the tyre friction coefficient which is the main parameter of the road surface type and condition. It was revealed that these parameters of the road surface have their effect on the parameters of a signalized intersection, i.e. cycle length and timing. The study showed that there is a correlation between this value (friction coefficient) and the capacity of the managed area (saturation flow) resulting in the change of the traffic lights cycle, which is also corroborated by the conducted field experiment on a signalized intersection. Saturation flow rates for the main road surface types and conditions were calculated (dry and wet asphalt, snowy and icy surface). The values of cycle length increase required in case of change of the road surface type or condition were defined.

Performance evaluation of the inside intersection median-turn lane markings on the mobility and safety performance of signalized intersections in the Philippines and Japan

Signalized intersections are one of the key elements that play a vital role at road networks. The efficiency and safety levels of intersections can affect the operational performance of the whole system. In general, turning traffic, especially median-turning, has always been considered as the most problematic movement in the operation of intersections. This becomes more critical with high turning demand where exclusive turning lanes (single or double) can be assigned to provide larger capacities for these movements and to reduce conflicts with through traffic. However, improper treatment of median-turn lanes could create cross-maneuvering behavior which may limit the expected increase in capacity and create safety issues. Median-turning lane markings are commonly provided at intersections in Japan to guide drivers while turning which is expected to reduce the conflicts among turning traffic. Meanwhile, in the Philippines, exclusive median-turn lanes are installed at intersections without proper treatment which may contribute to the low mobility and safety levels. Therefore, this study evaluated the impact of inside intersection lane markings on the operation of median-turn lanes in terms of mobility and safety. The vehicle maneuver, speed and interactions between the turning traffic were utilized as essential components for the assessment. The empirical analysis shows that conflicting trajectories were present on double turn lanes without median-turn lane markings in the Philippines, which resulted to serious conflicts among the turning vehicles and negatively influenced the turning speed and saturation flow rate of the turn lanes. On the other hand, the turn lane markings in Japan, provided a positive impact to mobility and safety of the turning lanes. Moreover, it was also found that the geometric characteristics and traffic signal phasing scheme highly affects the capacity and safety condition of signalized intersections.