Documents published in Scipedia

• Impact of Bottleneck Merge Control Strategies on Freeway Level of Service

  O. Ramadan, V. Sisiopiku

  Collection of Transportation Research Procedia (2017).

  
  

  Abstract

  Freeway work zones typically mandate lane closures that often induce bottlenecks. Merge maneuvers and the accompanying increase in the rate of lane changes at these bottlenecks can become problematic resulting in undesirable mobility and safety impacts. Traditionally, merge control strategies are deployed to mitigate such impacts. Literature sources indicate that available merge control strategies fall into one of four categories, namely: (i) early merge control, (ii) late merge control, (iii) temporary ramp metering, and (iv) mainline merge metering. However, little is known about the proper criteria for selecting and implementing one of the available merge control strategies. In addition, the impact of the various control strategies on freeway Level of Service (LOS) is currently under-researched. The purpose of this study is to evaluate the operational impacts of the above-mentioned freeway merge control strategies. The goal is to provide work-zone-aware LOS indicators that would help transportation agencies in selecting the most appropriate merge control strategy to minimally impact the freeway operations. In order to meet the research goals and objectives, this study used the CORSIM micro-simulation platform to evaluate impacts of various merge control strategies at a freeway study corridor in Birmingham, AL. The 2010 Highway Capacity Manual methods for calculating LOS were considered and modifications were proposed to align the calculated LOS with the assessed impacts of each merge control strategy. This study is significant for its contribution to providing transportation researchers and professionals with tools and methods to evaluate freeway LOS under work zone conditions and assisting them in mitigating the adverse impacts of work zones on traffic operations.

  Abstract
  Freeway work zones typically mandate lane closures that often induce bottlenecks. Merge maneuvers and the accompanying increase in the rate of lane changes at these bottlenecks [...]

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• Capacity and Delay Estimation at Signalized Intersections Under Unsaturated Flow Condition Based on Cycle Overflow Probability

  N. Wu, S. Giuliani

  Collection of Transportation Research Procedia (2017).

  
  

  Abstract

  Capacity at signalized intersections is a basic parameter in urban transport networks. The capacity of a signalized intersection is a function of existing geometric, control, weather, and other conditions. Estimation of capacity at signalized intersections is one of the most important topics in traffic Engineering. If the capacity can directly be measured, the delay at signalized intersections and thus the traffic performance and quality of service can be calculated according to the functional relationship between delay and capacity. Unfortunately, under real world traffic conditions, the capacity cannot easily be measured directly for an existing intersection, especially under unsaturated flow conditions where the flow volume is lower than the capacity. This paper presents a model for estimating the capacity of an existing signalized intersection under unsaturated flow condition based on the cycle overflow probability which can be directly measured by loop detectors at stop lines. The cycle overflow probability is just the proportion of cycles with occupied detector at end of green time phases. Also the flow volume can directly be measured by loop detectors at stop lines. According to the queuing theory, the cycle overflow probability is a function of the degree of saturation, i.e. a function of flow volume and capacity. Thus, by measuring the cycle overflow probability and the flow volume, the capacity can be estimated according to the functional relationship. The proposed model is calibrated to data obtained from loop detectors at different signalized intersections under unsaturated conditions. For validation the model, the real capacities at the same intersections are measured for saturated cycles where the capacity can be considers as the measured volume. The proposed model delivers a useful tool for estimating capacity at signalized intersections under unsaturated conditions. Using the proposed model, the capacity and thus the traffic quality of service at existing signalized intersections can directly be estimated using data from loop detectors at stop lines. The model is theoretically reasonable and easily to use for practitioners. The results of the calibration and validation are very promising.

  Abstract
  Capacity at signalized intersections is a basic parameter in urban transport networks. The capacity of a signalized intersection is a function of existing geometric, control, [...]

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• The New Procedures for Diverge, Merge, and Small Weaving Segments in the New Version of German Highway Capacity Manual (HBS 2015)

  N. Wu, K. Lemke

  Collection of Transportation Research Procedia (2017).

  
  

  Abstract

  The first version of German Highway Capacity Manual was published in 2001. Now, a new version is published in 2015 (HBS 2015). For the new German Highway Capacity Manual, most major chapters are revised and some of them are totally rewritten. The chapter for merge, diverge, and small weaving segments is rewritten in accordance with forthcoming developments in the past 10 years. In this paper, an overview of the chapter in the new German Highway Capacity Manual is presented. Procedures dealing with performance analyses and level of service (LOS) of those segments are introduced both for freeways and rural highways. Differences between the former version and the new version of the chapter in the German Highway Capacity Manual are indicated and discussed. In most of the existing highway capacity manuals, LOS of merge, diverge, and small weaving segments is traditionally defined by speed, volume, or density in critical areas. In that traditional concept several capacity values of different critical areas (merge, diverge, and weaving) as well as upstream and downstream basic segments within the influence areas are evaluated separately. In the new HBS 2015, a new model which considers the total merge, diverge, and weaving segment as an entire object is incorporated. A combined volume-to-capacity ratio (freeways) or a combined density (rural highways) is used for defining the LOS of the total segment. The parameters of the new procedure are functions of the number of lanes of the major road, the number of lanes in the on-ramp or off-ramp, and the predefined geometric design of those segments. The coefficients are calibrated with field data or defined by experts’ experiences within a matrix of coefficients. With those procedures, the traffic quality (LOS) can be obtained directly as a function of the volumes or densities on the major road and on the on-ramp or off-ramp respectively. The new procedure has the following advantages: a) a uniform function for all types of merge, diverge, and small weaving segments, b) traffic quality assessment for all critical areas under investigation in one step, and c) the procedure can easily be calibrated. For applications in practice, a set of graphs is provided.

  Abstract
  The first version of German Highway Capacity Manual was published in 2001. Now, a new version is published in 2015 (HBS 2015). For the new German Highway Capacity Manual, [...]

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• Saturation Flow Rate Analysis at Signalized Intersections for Mixed Traffic Conditions in Motorcycle Dependent Cities

  H. Nguyen

  Collection of Transportation Research Procedia (2017).

  
  

  Abstract

  This article describes the results of a comprehensive saturation flow rate analysis at signalized intersections in motorcycle dependent cities. Most of current capacity analysis methods for signalized intersections consider vehicles moving on lanes, and they assume lane discipline and high driver discipline regarding traffic regulations. Moreover, for modeling mixed traffic conditions, the not lane-based heterogeneous real traffic flow is transferred into lane-based homogeneous flow by using Passenger Car Units. So far, available methods of capacity analysis do not consider the specific conditions of driver behaviour and traffic flow which are dominant e.g. in Vietnam or other countries where motorcycles have the major share in traffic. Consequently, there is a need to develop a proper method to allow such saturation flow rate analysis. The methodology of this research was developed with consideration of the specific traffic situation in Hochiminh City, Vietnam, a motorcycle dependent city. First, the article describes the unique aspects of traffic flow and saturation flow rate analysis under such mixed traffic conditions compared with car-dominated traffic, using data collected by observations of saturated flow conditions at 12 signalized intersections. Then, saturation flow rate models using a regression method are presented and described. The term of Motorcycle Unit (MCU) is introduced, and a set of factors which mainly affect the saturation flow in such mixed conditions is developed. These factors reflect major differences between the traffic flows under saturated conditions at signalized intersections in motorcycle dependent cities and car-dominated cites. For example, this includes the influence of the approach width, the impact of four-wheel vehicles (including car, bus, and truck) on motorcycles, the very specific interactions of left-turning and opposite straight-moving traffic streams, the relationship between right-turning 4-wheel vehicles and motorcycles moving straight in the same direction, and the phenomenon of capacity drop within the green time. Finally, a procedure to calculate the saturation flow rate for specific traffic situations is provided, and the application of the proposed model is depicted. The conducted research indicates that the proposed saturation flow rate analysis model is an appropriate approach to calculate the saturation flow rate for traffic streams at signalized intersections under such mixed traffic conditions. The set of motorcycle equivalent units used for analysis is also proved to be suitable for this model. Equations and graphs to determine the appropriate values for the identified influencing factors are presented. According to each specific traffic situation, calculation procedures are provided to determine the value of the saturation flow rate.

  Abstract
  This article describes the results of a comprehensive saturation flow rate analysis at signalized intersections in motorcycle dependent cities. Most of current capacity analysis [...]

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• Human Ellipse of Indian Pedestrians

  N. Singh, P. Parida, M. Advani, R. Gujar

  Collection of Transportation Research Procedia (2017).

  
  

  Abstract

  The most important parameter for designing a pedestrian facility is the area required by a pedestrian to stand comfortably or make a comfortable movement. This area is referred as Body Ellipse (Human Ellipse) and depends on Shoulder Width and Body Depth of a human being (and also on the kind of activity i.e. Standing or Walking). In current practices, design of pedestrian facilities’ are according to the body ellipse of pedestrians experimented in The United States Of America (US-HCM 2010). Regional variances are marked in these physical characteristics that are dependent on human body dimensions to a greater extent, ultimately playing an important role in pedestrian’s convenience (capacity and Level of service of a facility) and design environment. This paper is an attempt to study the measurements of Body Ellipses i.e. body depth and shoulder width by carrying out videography surveys on the pedestrians in India (specifically Delhi). The analysis also includes, classifying the body dimensions according to gender and walking with/without baggage (handbag/backpack), along with the measurement of the Step length of pedestrians’ while walking which shall give out the area required for walking. These body dimensions have been compared with the standard body dimension available worldwide. The study location was a walkway in a commercial area in Delhi (India) with a sample size of 747 consisting of 132 females and 615 males. The extracted body dimension varies from 26.07 to 52.14 centimeter for body depth and 42.35 to 67.76 centimeters for shoulder width.

  Abstract
  The most important parameter for designing a pedestrian facility is the area required by a pedestrian to stand comfortably or make a comfortable movement. This area is referred [...]

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• Shockwave Suppression by Vehicle-to-Vehicle Communication

  N. Motamedidehkordi, M. Margreiter, T. Benz

  Collection of Transportation Research Procedia (2017).

  
  

  Abstract

  The rapid development of wireless communication and information technologies has increased research interests in inter-vehicle communication systems and their effect on traffic flow. One of the most complex traffic phenomena on freeways are shockwaves. Shockwaves are recognized as the sudden, substantial change in the state of the traffic flow, which acts as an active or moving bottleneck. They have significant impact on freeway capacity and safety. For this study, a microscopic traffic simulation was used to determine the extent to which inter-vehicle communication and change in the driving strategy after the recognition of a shockwave can influence the propagation and dissolving of shockwaves on freeways. We also briefly introduce the shockwave theory and our communication algorithm. Then we present the simulation result with different penetration rates of communicative vehicles, which are randomly dispersed in traffic flow, through performance measures for traffic flow with shockwaves.

  Abstract
  The rapid development of wireless communication and information technologies has increased research interests in inter-vehicle communication systems and their effect on traffic [...]

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• An Analysis of Heavy Vehicle Impact on Roundabout Entry Capacity in Japan

  N. Kang, H. Nakamura

  Collection of Transportation Research Procedia (2017).

  
  

  Abstract

  Heavy vehicles behave differently from ordinary passenger cars due to their characteristics such as size and operational performance. At roundabout, entry capacity estimation mainly focuses on passenger cars. In HCM 2010, the impact of heavy vehicles on entry capacity is considered through a heavy vehicle adjustment factor fHV which includes heavy vehicle percentage and passenger car equivalent (PCE hereafter) value. It is generally set as 2.0, which means a heavy vehicle is assumed to be equivalent to two passenger cars. In existing methods, the PCE value at roundabouts is estimated based on several considerations such as entry capacity and move-up time. All of these considerations are influenced by local driver behavior and geometry conditions. Thus, this paper aims to estimate entry capacity considering the characteristics of heavy vehicle behavior in Japan. In this paper, characteristics of heavy vehicle behavior such as speed and gap parameters are firstly analyzed by using data observed at several roundabouts in Japan. Then, a simulation study which is calibrated based on the observation data is conducted by applying VISSIM 5.40. Roundabout entry capacity is estimated through assuming different heavy vehicle percentage values of each entry. Based on the estimated results of entry capacity, PCE value is calculated. The PCE values from the simulation study are compared with those values adopted by several design guidelines. Through the empirical analysis, it is found that heavy vehicles move in lower speed than passenger cars in the process of travelling roundabouts. The headways which are formed by heavy vehicles are commonly greater than those only formed by passenger cars. Then, PCE values which are calculated from simulation output are shown to change with different combinations of heavy vehicle percentage of each entry. The results in this paper provide a reference for roundabout entry capacity estimation considering heavy vehicle behavior in Japan. Future works are some further analysis from the viewpoint of geometry, since heavy vehicle behavior is significantly influenced by roundabout geometry such as inscribed circle diameter and circulatory roadway width, particularly at compact roundabout which is often the case in Japan.

  Abstract
  Heavy vehicles behave differently from ordinary passenger cars due to their characteristics such as size and operational performance. At roundabout, entry capacity estimation [...]

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• A Rationale for Enhancing the German Highway Capacity Manual to Incorporate Oversaturated Freeway Facility Analysis

  M. Hartmann, P. Vortisch

  Collection of Transportation Research Procedia (2017).

  
  

  Abstract

  Unlike the U.S. 2010 Highway Capacity Manual, the most recent edition of German Highway Capacity Manual does not include methodology to evaluate the facility within oversaturated time periods. To incorporate this traffic flow regime within the methodology, we identify several aspects of the methodology that require enhancements and propose modifications. Next, we implement these modifications in a macroscopic traffic model developed as a software implementation of the German guideline. In this manner, the HBS user can conduct traffic flow analysis that includes volume-to-capacity ratios above 1.00 which has not been foreseen by the guideline until now. The main contribution of this paper is the identification of methods within the German Highway Capacity Manual that require modification to enable incorporation of oversaturated traffic flow within the analysis. Further, we introduce traffic density as a variable within the HBS methodology and show benefits of its incorporation during the oversaturated time periods. Finally, the paper includes illustrative examples of empirical and model-based evaluation of congested freeway facility in Germany. The paper concludes with a discussion of proposed methods and their limitations.

  Abstract
  Unlike the U.S. 2010 Highway Capacity Manual, the most recent edition of German Highway Capacity Manual does not include methodology to evaluate the facility within oversaturated [...]

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• Capacity and Operational Improvements of Metering Roundabouts in Spain

  M. Martin-Gasulla, A. Garcia, A. Moreno, C. Llorca

  Collection of Transportation Research Procedia (2017).

  
  

  Abstract

  Roundabouts show great advantages due to their geometry and their priority system, both in terms of capacity and road safety, compared to other intersections. However, unbalanced flows may be a problem even at medium demand levels. One single approach may cause queues on the downstream approaches as drivers are not allowed to entry the roundabout. If that downstream approach has the highest flow demand, average delay is highly increased, so, the roundabout can be collapsed. This operational problem is derived from one of roundabouts fundamental properties: movements with greater traffic demand cannot be prioritized, unlike signalized intersections. A few solutions may be found, but the most cost-effective measure is traffic regulation by metering signals. The aim of the research is to analyze capacity improvements and operational performance on roundabouts with metering signals using traffic microsimulation, for Spain local conditions. Metering signals are based on creating gaps in the circulating stream in order to alleviate excessive delays on the main approach of the roundabout. Consequently, they are used only on heavy demand conditions during peak hours. On the metered approach, which causes problems for a main downstream approach (controlling approach), metering signals are implemented. The metered approach is stopped by red signals controlled by a queue detector on the controlling approach. So, the controlling approach is benefited by metering signals as drivers can easily enter the roundabout, and the roundabout overall traffic operation is improved. The research was conducted in 5 stages: roundabouts selection, field study, calibration and validation of a traffic microsimulation model in VISSIM, generation of multiple scenarios, and, analysis of the results. Two roundabouts with known unbalanced flow patterns on Valencia (Spain) were selected, traffic counts were carried out to describe their traffic flow patterns, which resulted on limited capacity at both locations. In order to quantify traffic operation improvement on metered roundabouts, a traffic microsimulation model in VISSIM was elaborated. The model was calibrated and validated using critical gaps, queues, delays, and speeds. Afterwards, a metering signal technique was implemented on VisVAP, based on an ad hoc signal control logic design. Almost 400 combinations of design and control metering signals parameters were required to obtain the optimal model (distances to yield line, red and green time settings) which presented the lowest average delay. It could be concluded that, for the same medium-high circulating flow, a higher demand would be able to enter the roundabout (of up to 80% from the controlled approach) with less average delay values (22% and 56% at each studied roundabout) by installing metering signals.

  Abstract
  Roundabouts show great advantages due to their geometry and their priority system, both in terms of capacity and road safety, compared to other intersections. However, unbalanced [...]

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• Automatic Incident Detection Based on Bluetooth Detection in Northern Bavaria

  M. Margreiter

  Collection of Transportation Research Procedia (2017).

  
  

  Abstract

  This work describes an approach to determine the current travel times on freeways based on the detection and re-identification of Bluetooth devices onboard of vehicles using stationary roadside Bluetooth detection technology. It also aims at using this information for the traffic state determination of a whole freeway network with the goal of a fast and reliable dynamic net control in incident situations. Based on a four year experience in a Bluetooth detector test bed in Northern Bavaria, Germany, and after the evaluation of hundreds of millions of single detections, the technology as well as the developed algorithms for validation and evaluation of the data show their feasibility in practical use, especially in areas with a low density of stationary detectors like inductive loops. The data-driven part of the approach is divided into three subsequent steps. These steps are the determination of travel times, the data filtering and validation of plausible travel times and the automatic incident detection. The determination of travel time is based on the time stamp of the detection of a Bluetooth device with the shortest estimated distance to the position of the Bluetooth detector. For the data filtering the “Time Dependent Comparison to Neighbor Values Filter” will be applied. This filter allows for a fast and reliable differentiation between unrealistic (due to stops, detours, back and return trips etc.) and plausible travel time values for a certain segment of the freeway and is based on a method to validate if the determined travel time is in a plausibility threshold corridor defined by the values of the previous and the next neighboring travel times. The outcome is a detailed travel time information for the whole freeway network which is used for an automatic incident detection, which was developed and calibrated within this research project. This includes the detection of the start of an incident as well as the end of an incident. The result is continuous information about the prevailing travel times and a fast and reliable traffic state information for all segments, which allows for a dynamic large-scale re-routing in the Bavarian freeway network in case of congestions or other disturbances of the traffic flow.

  Abstract
  This work describes an approach to determine the current travel times on freeways based on the detection and re-identification of Bluetooth devices onboard of vehicles using [...]

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