Estimation Of Critical Gap Research Articles

Realistic Approach for Capacity Estimation of U-Turns Under Heterogeneous Traffic Condition

The main purpose of the present study is to estimate U-turn capacity at mid-block median openings (MBMO). Estimation of U-turn capacity requires three key parameters, namely: conflicting traffic volume, critical gap, and follow-up time. Conflicting traffic volume has been estimated by introducing a novel parameter, namely, spatiotemporal conflicting factor. Critical gap has been estimated using five different methods: modified Raff method, Ashworth method, logit model, occupancy time method, and support vector machine technique. The follow-up time has been estimated directly from recorded videos. Subsequently, capacity has been estimated for different types of vehicles along with the U-turning stream capacity. The estimated capacity has been validated using field capacity, using Kyte’s method. Further, a suitable method for the estimation of critical gap in the Indian context has been determined. This study could be used as a guideline for the U-turn capacity estimation for efficient design and management of traffic at MBMO.

Accuracy of critical gap estimates

The critical gap is an important parameter in capacity models of unsignalized intersections. Although there are many methods for critical gap estimation, there is currently no approach or method available to determine how precise a calculated estimate is, i.e. how close it is to the true mean critical gap. As a result, traffic engineers and researchers risk unknowingly working with imprecise estimates, which can lead to inaccurate or unreliable capacity analyses of unsignalized intersections. The purpose of this paper is to address this problem by providing new methods for measuring the accuracy of critical gap estimates. We focus on estimates obtained by the maximum likelihood method (using the so-called Fisher information), but a method for measuring the accuracy of arbitrary estimation methods (the Bootstrap method) is also provided. The paper shows how the proposed methods help to assess the quality of critical gap estimates, detect imprecise estimates, and provide guidance on how many observations should be made for the calculated values to be sufficiently precise. Specifically, we recommend that at least 100 observations should be made to generally obtain reliable estimates. For ease of use, an Excel spreadsheet implementing the proposed methods is provided.

Impact of Inconsistent Behavior of Drivers on Estimation of Critical Gap at Multi-Lane Roundabouts

Critical gap (CG) estimation, while taking into consideration inconsistent driver behavior resulting from heterogeneous traffic conditions, is a tedious task. Several methods dealing with CG estimation have been developed in the past but limited research has been done in this regard for developing countries and there is a lot of scope to explore this field considering varying traffic conditions on the roads. In this study, the maximum likelihood method (MLM), one of the most prominent methods of determining CG, has been compared with two other methods developed for traffic conditions prevailing in India. These methods use different techniques for calculating the CG, such as minimization of absolute differences of gaps given by Ahmad et al., and minimization of square root of standard deviation of actual gap value from the predicted CG as per the Indian Highway Capacity Manual (Indo-HCM). This paper discusses the estimation of CG for five different categories of vehicles using these methods to counter the heterogeneity of traffic. Data has been collected on two urban multi-lane roundabouts in India. SOLVER in MS Excel is used to optimize the functions defined in all three methods. The results reveal that the method suggested by Ahmad et al. gives the most consistent results which are close to actual value when driver behavior is inconsistent. The other two methods are also reasonably consistent, with the method given in Indo-HCM being slightly better than MLM. Further, two-way ANOVA was applied to check the consistency of results.

Implementing the Maximum Likelihood Method for Critical Gap Estimation under Heterogeneous Traffic Conditions

Gap acceptance analysis is crucial for determining capacity and delay at uncontrolled intersections. The probability of a driver accepting an adequate gap changes over time, and in different intersection types and traffic circumstances. The majority of previous studies in this regard have assumed homogeneous traffic conditions, and applying them directly to heterogeneous traffic conditions may produce biased results. Moreover, driver behavior concerning critical gap acceptance or rejection in traffic also varies from one location to another. The current research focused on the estimation of critical gaps considering different vehicle types (cars, and two- and three-wheelers) under heterogenous traffic conditions at uncontrolled crossings in the city of Peshawar, Pakistan. A four-legged uncontrolled intersection in the study area was used to investigate drivers’ gap acceptance behavior. The gaps were investigated for various vehicle types: two-wheelers, three-wheelers, and cars. For data collection, a video recording method was used, and Avidemux video editing software was used for data investigation. The study investigated the applicability of the maximum likelihood (MLM) method to analyzing a vehicle’s critical gap. MLM estimation results indicate that the essential critical gap values for car drivers are in the range from 7.45 to 4.6 s; for two-wheelers, the critical gap was in the range from 6.78 to 4.7 s; and for three-wheelers, the values were in the range from 6.3 to 4.9 s. At an uncontrolled intersection, the proposed method’s results can assist in distinguishing between different road user groups. This study’s findings are intended to be useful to both researchers and practitioners, particularly in developing countries with similar traffic patterns and vehicle adherence patterns at unsignalized intersections.

Critical Gap Estimation and Its Implication on Capacity and Safety of High-Speed Un-Signalised T-Intersection under Heterogeneous Traffic Conditions

In India, priority rules at un-signalized intersections are often ignored by drivers. The present paper reports the applicability of deterministic and probabilistic methods for estimating the critical gaps at high-speed un-signalized T-intersections. The critical gap is estimated for different vehicle types and crossing movements. The study quantifies the implication of critical gap values on the capacity and safety values at un-signalized T-intersections. The results point to conclusion that the value obtained for the critical gap using deterministic methods is lower than that estimated by the probabilistic method. The gap values estimated using the Binary Logit Regression method are similar to those computed using the equation reported in Indo-HCM (2017). It was concluded that a lower value of the critical gap yields a higher capacity value and a higher value of risk probability.

Relationship between Critical Gap and Certain Geometrical Parameters in Roundabouts

Gap-acceptance method is one of the classical methods used to analyze capacity of roundabouts. Critical gap has a privileged role in this approach. Different driver behavior and local rules of traffic has a key role in implementing it in the local standard for capacity calculation in each country. Therefore, a reliable method for estimation of critical gap at a certain location can be of great importance. This paper presents the first steps of an experimental investigation and analysis on whether it is possible to find correlation between video-based gap acceptance data and certain design parameters of roundabouts in Hungary. Ten single lane roundabouts of different size were recorded for hours in different locations in and around Budapest to assess gap acceptance data and relate it to certain design parameters like diameter, distance of neighboring entries, entry width, width of splitter island, number of entries over time, and entry angle – or any combination of those. Using only a linear approach, strong positive correlation was found between measured critical gap and distance between legs. There is correlation (not so strong however) between critical gap and (approach) entry width as well as splitter island width, and enough data were examined to say that there is no correlation between central island diameter and critical gap.

Critical Gap in Roundabouts – A Short Comparison of Estimation Methods

Gap-acceptance method is one of the classical methods used to analyze the capacity of roundabouts. Critical gap has a privileged role in this approach. Different driver behavior and local rules of traffic have key role in implementing gap-acceptance method into the local standard for capacity calculation in each country. Therefore, a reliable method for estimation of critical gap at a certain location can be of great importance. This paper presents an experimental investigation and analysis on whether it is possible to find differences between estimating critical gap using video-based gap acceptance data of roundabouts in Hungary. Three single lane roundabouts of different size were recorded for hours in different locations in Budapest and Érd to assess gap acceptance data. Three different methods or models were used to estimate critical gap and no significant differences were found between their results.

Critical Gap Estimation and its Implication on Capacity and Safety of High-Speed Un-Signalized T-Intersection Under Mixed Traffic Conditions

Critical Gap Estimation and its Implication on Capacity and Safety of High-Speed Un-Signalized T-Intersection Under Mixed Traffic Conditions

Comparative Appraisal of Critical Gap Estimation Techniques in the Context of U-turning Vehicles

Critical gap is a crucial factor for capacity estimation and safety evaluation at uncontrolled mid-block median openings (MBMOs). The U-turning vehicle makes a U-turn when a sufficient gap between two fast-moving vehicles is available in the approaching through traffic (ATT) stream. Even though, worldwide, temporal gaps are extensively used, the spatial gap is an important parameter that significantly affects minor street vehicles’ safety (U-turning vehicles in this study). The present research, undertaken in India, focuses on estimating the temporal and spatial critical gap of U-turning vehicles at uncontrolled MBMOs. The collected data were analyzed for six different types of U-turning vehicles at varying approaching through traffic volume (ATTV). For critical gap estimation, four different critical gap estimation techniques, namely, modified Raff method (MRM), Ashworth method, binary logit model (BLM) method, and occupancy time (OT) method were employed, separately. From the analysis, temporal and spatial critical gaps were observed to vary between different types of vehicle, and it was also observed to vary with ATTV. The critical gap values of this study were found to be smaller than the critical values reported in developed countries, signifying the aggressive driving nature of drivers in developing countries. A detailed appraisal of the different critical gap estimation methods has been carried out. From this analysis, the OT method was found to provide the closest critical gap values with the published literature compared with other methods. Lastly, the findings from the present study will be useful for capacity estimation and safety evaluation at MBMO.

A method for estimating pedestrian critical gap using microsimulation

Estimating critical gap is crucial for modelling pedestrian level of service at crossings. Critical gap modelling becomes more challenging in signalized crossings because the proportion of pedestrians seeking gaps during red is usually unknown. Besides, the willingness – or lack of it – to cross during red signal indication varies by pedestrian and local characteristics, which makes gap acceptance modelling even more challenging. The main objective of this study is to propose a method for estimating pedestrian critical gap at signalized crossings using Vissim. The method considers that all pedestrians seek for gaps on red, and the critical gap parameter is calibrated for each pedestrian type having delay as calibration target. The results showed MAPE values of 2% and 9% for the two studied crossings. This method was compared to three existing methods of critical gap estimation. The results showed that the proposed method yielded the best estimations of delay, followed by the HCM’s.

Estimation of Critical Gap Using Maximum Likelihood Method at Unsignalized Intersection: A Case Study in Adama City, Ethiopia

Studying Critical gap and headway distribution has vital role in reduction of traffic problems. Critical gap and its distribution are traffic characteristics that are used in determination of capacity, delay and level of service at unsignalized intersection. Many study has been done on critical gap in developed countries under homogeneous traffic and road conditions. This study is aimed to insight available headway distribution and critical gap of driver in urban intersection under heterogeneous traffic condition and weak lane discipline in developing country like Ethiopia. In this paper three unsignalized intersection in Adama city has been selected on the basis of traffic volume and importance of the intersection. The primary data that were used for this study were traffic volume, available headways, waiting time, geometry of road. By using digital Camera, videos data were recorded; later quantitative data were extracted from videos. Two Statistical Packages that were used in analysis of this study. Statistical Package for Social Science Statistic 20 was used to fit best distribution model of headway. Kolmogorov Smirnov and Anderson Darling testing techniques were conducted to check validity of model for headways in different flow ranges. From hypothesized distributions, exponential, gamma, lognormal and normal distributions were selected for different intersection. It has been indicated that, for higher flow rate lognormal distribution model is best fit in estimating cumulative density function of headway. Critical gaps of drivers for three selected intersections were also computed by using maximum likelihood method. Through Comparison of estimated values indicates that, Franko intersection has highest critical gap of 5.17sec.

Critical gaps at three-legged unsignalised intersections using microsimulation

The aim of this study was to explore the viability of microsimulation in estimating critical gaps at unsignalised intersections. Critical gaps are generally estimated by extracting gap acceptance data from traffic videos. Extracting such data is a strenuous task, especially under mixed traffic conditions. In this study, gap acceptance data were generated from simulation models developed in the Vissim software package. Critical gaps of three unsignalised intersections were estimated using field data and simulated data of the intersections. Critical gaps were estimated by the logit method and the clearing time method. The critical gaps estimated using simulated data were reasonably close to those obtained using field data for both methods. The results also showed that the logit method was more robust than the clearing time method in estimating critical gaps under mixed traffic conditions. Moreover, the time needed for generating simulated data was only 3.6% of that required for obtaining field data. The method proposed in this study will help traffic engineers and practitioners in critical gap estimation by saving a considerable amount of time and effort.

Estimation of critical gap of U-turns at uncontrolled median openings considering Iran’s driver behavior

ABSTRACT The critical gap is typically used to determine the capacity at unsignalized intersections. A few studies have been carried out on the estimation of the U-turn critical gap at uncontrolled median openings. In this research, the critical gap was calculated using four well-known methods, Maximum Likelihood Method (MLM), Ashworth’s, Raff, and acceptance curve for different types of U-turn vehicles at four uncontrolled median openings in Iran. The data were collected using video recording. The results showed that MLM is the best method for calculating the critical gap according to the conditions of Iran. According to this method, the average critical gap was obtained 3.23 seconds, which was very low compared to other countries. Moreover, the result of MLM showed that the critical gap for Heavy Vehicles (HVs) drivers was almost less than car drivers, indicating the behavior of HVs drivers was more aggressive.

Investigation of Critical Gap for Pedestrian Crossing Using Fuzzy Logic System

This paper assesses pedestrian crossing behavior and critical gaps at a two-way midblock crossing location. A critical gap is the shortest gap that a pedestrian accepts when crossing a road. A dataset was collected in 2017 in Edinburgh (UK). The analysis was performed using the fuzzy logic system. The adopted membership function of the fuzzy logic system is of a triangular form since it has a simple and convenient structure. The input variables that are used in the analysis are the number and length of rejected gaps and length of accepted gaps at the crossing location. The output variables are the critical gaps. The results show that assessing critical gap estimation of pedestrians crossing using fuzzy logic is achievable and produces reasonable values that are comparable to values that are reported in the literature. This outcome improves the understanding of pedestrian crossing behavior and could therefore have implications for transport infrastructure design. Further analysis using additional parameters including waiting time and demographic characteristics and alternative forms for membership functions are strongly encouraged.

Aplicação de métodos determinísticos para a obtenção de gap crítico em rotatórias urbanas brasileiras

O presente estudo tem o objetivo de avaliar o gap crítico e o follow-up headway para rotatórias brasileiras e comparar com estudos estrangeiros. Para tanto, foram selecionadas três rotatórias brasileiras de duas faixas de circulação e de entrada. Para a obtenção de gaps críticos foram utilizados cinco métodos determinísticos: Siegloch (1973), Raff (1950), Miller & Pretty (1968), Wu (2012) e Bunker (2012), sendo que pelo primeiro método foi possível obter também o follow-up headway. Os valores de gaps críticos foram consideravelmente diferentes em função da faixa utilizada: na faixa da direita, os motoristas aceitam gaps menores para entrar na interseção. Esta diferença não foi significativa quando se trata de valores de follow-up headway. Em seguida, os métodos de estimação de gap crítico foram validados comparando a capacidade das interseções pelo método de Hagring (1998) com dados de fluxos agregados por minuto. Finalmente, os valores brasileiros foram comparados com dados estrangeiros e foram verificadas semelhanças com países como Suíça, Itália e Portugal.

Analyzing variations in spatial critical gaps at two-way stop controlled intersections using parametric and non-parametric techniques

At two-way stop controlled (TWSC) intersections drivers on minor stream are generally at risk because of the difficulty in judging safe gap between major stream vehicles. Any misjudgment by the driver while choosing gap may result in a collision with major stream vehicle. This paper provides important insights for determining and analyzing spatial critical gaps of drivers at high speed and medium speed TWSC intersections. The critical gap line (CGL) fitted for the accepted and rejected gaps using parametric (binary logit model-BLM) and non-parametric (support vector machines-SVM) techniques gives critical gap values at 15th, 50th and 85th percentile speeds. The evaluation of spatial critical gap with respect to major road vehicle (conflicting vehicle) speed makes it easier to understand the impact of variation in speed on spatial gaps accepted by the drivers on the minor road. The logit models developed revealed that the probability of accepting gap decreases with increase in the speed of the conflicting vehicle and it increases with increase in the distance of conflicting vehicle. The spatial critical gaps estimated using support vector machines were found in close approximation with those estimated using binary logit model. The study results showed that SVMs have very good potential to be an alternative tool for the estimation of driver's critical gap. The spatial critical gaps corresponding to 15th, 50th and 85th percentile speeds for medium speed intersections were 32 m, 38 m and 46 m respectively and for high speed intersections these values were 64 m, 76 m and 104 m respectively. The increase in the magnitude of gap value with respect to the percentile speed clearly states the effect of speed on spatial gaps. The insights from the study can be used to suggest various measures to improve the safety of crossing drivers at uncontrolled intersections. • The study provides important insights for analyzing spatial critical gaps at high speed and medium speed uncontrolled intersections. • BLM and SVM are used as a linear classifiers to fit decision boundary between accepted and rejected gaps. • The spatial critical gaps estimated using BLM and SVM corresponding to 85th percentile speed are 46 m and 45 m respectively. • SVMs have very good potential to be an alternative tool for the estimation of driver's critical gap.

Estimation of critical gap at small roundabout

The gap acceptance theory is basically implied to describe the driver’s behavior in the minor stream at the entry of roundabout searching for a suitable gap at the major stream to merge. The critical gap is an important parameter in the gap acceptance theory. However, the critical gap cannot be measured directly on the field. One way to measure the critical gap is by measuring only the rejected and accepted gaps. This study attempts to determine the critical gap at small roundabout using three different methods namely Raff’s Method, Wu’s Method, and Simple Logit Method. The data is collected at a two-lane roundabout in Skudai – Johor Bahru at the morning and afternoon peak hour using video camera technology. Accepted and rejected gaps are then extracted from the recorded videotape. The accepted and rejected gaps obtained are analysed to determine the critical gap. The findings from the study reveal that the critical gap values from the three methods are almost similar, having a critical gap of 3.45s, 3.60s and 3.45s for Raff’s Method, Wu’s Method, and Simple Logit Method respectively.

Critical Gaps at Unsignalized Intersections with Bending Right-of-Way

The capacity calculation procedure for unsignalized intersections is based on the gap-acceptance theory in most of existing capacity regulations and it relies on one of the important parameters - critical gap. However, the capacity calculation procedure and values of critical gaps according to these regulations are valid only for intersections with standard right-of-way (major street leading straight). Nevertheless, in Slovakia, intersections with bending right-of-way (major street not leading straight, but bending) can be encountered. The specific mode of right-of-way results in different priority ranks of traffic movements (set by traffic rules of driving), more complicated traffic situation and therefore, different driver behaviour characteristics. To examine the gap acceptance behaviour of drivers under these specific conditions, an unsignalized four-leg intersection with bending right-of-way located in an urban area of Zilina, Slovakia, was selected. Three different methods (Raff, Wu, and MLM Troutbeck) were used for critical gap estimation from the field data. In the article, results of critical gaps for three through movements of different priority rank (major-street through movement of Rank 2 and minor-street through movements of Rank 3 and 4) are presented. The results show, that the values of critical gaps differ depending on the method by about 3-5 % only, which is not significant. Troutbeck ´s MLM method gives the highest values. The priority rank of movement has the greatest impact on the result. The values of critical gap for major-street through movement of Rank 2 are the smallest; they are approximately 1.3-2.1 s smaller than the values for minor-street through movements of Rank 3 or 4. The highest values of critical gap have been estimated for minor-street through movement of Rank 4 and they are higher compared to the current Slovak regulations TP 102 values for the same priority rank.

Calibração do modelo de aceitação de brechas em interseções urbanas com o microssimulador de tráfego VISSIM

Este artigo tem como objetivo principal propor um método para a modelagem do processo de aceitação de brechas em interseções urbanas não semaforizadas utilizando o microssimulador VISSIM. O método proposto tem como medida-alvo o tempo que o motorista leva no processo de avaliação das brechas, ou seja, o tempo de espera enquanto está na primeira posição da fila. O c2 da aderência entre as distribuições dos tempos de espera (simulados e observados) e a diferença entre as médias foram utilizados na estimação da brecha crítica. O método foi aplicado em uma interseção da cidade de Fortaleza. Os resultados indicaram valores levemente diferentes da brecha crítica entre os movimentos de conversão. O segundo objetivo deste trabalho é comparar o método proposto com o método de calibração mais convencional, no qual a medida-alvo é uma medida de desempenho do tráfego, como o tamanho médio da fila. O método proposto apresentou melhores resultados.

Application of Gap Acceptance Concept to Investigate Crossing Behaviour of Pedestrians at Unsignalized Intersections

In this study, an attempt has been made to study the gap acceptance behaviour of pedestrians to establish safety margins while crossing at unsignalized intersections. To examine the gap acceptance behaviour of the pedestrians, road geometric and traffic data were collected from 42 unsignalized intersections of seven Indian cities. Equilibrium probability method and maximum likelihood method were adopted for the estimation of critical gap of pedestrians on the basis of different demographic factors. Comparison between these two methods shows that equilibrium probability method is more suitable for estimating pedestrian critical gap at unsignalized intersections in mixed traffic condition. Analysis shows that the average critical gap for a young pedestrian is (5.31 s) less than that for a middle-aged (6.49 s) or old pedestrian (6.09 s), whereas regarding gender, the average critical gap for male is (5.7 s) less than that for female (6.1 s). It has been noted that with increase in critical gap, the crossing time increases logarithmically. Pedestrian safety margin model has been developed with the help of ridge regression technique. It was found that critical gap and crossing time had significant effect on the safety margin of the pedestrian. The model was validated with R2 value of 0.75 and the model output showed that 7% of pedestrians took high risk while crossing, as their safety margin was observed to be nearly zero.