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The current method for the analysis of sight distance for left-turn vehicles at signalized intersections assumes that all component variables are deterministic. This paper presents a probabilistic approach based on such random variables as major-road speed, time gap required for left-turn vehicle, vehicle width, lateral position of left-turn vehicle, distance between driver eye of left-turn vehicle and its front, and lateral and longitudinal positions of positioned opposing left-turn vehicle. A safety margin is defined as the difference between available and required sight distances. Relationships for the mean and standard deviation of the safety margin were developed using the first-order second-moment (FOSM) method. This method identifies the offset (distance between left edge of the left-turn lane and right edge of the opposing left-turn lane) at signalized intersections for a desired probability of noncompliance based on intersection and traffic characteristics. The proposed reliability method was validated using Monte Carlo simulation, and design graphs were established. The results show that the deterministic method provides very conservative offsets and that the offset is most sensitive to vehicle width and lateral distance-related variables and less sensitive to longitudinal distance-related variables. [ABSTRACT FROM AUTHOR]

Ramp metering has been proven as an effective freeway-management strategy; however, one of the critical challenges in design and operation of ramp metering is the lack of up-to-date design guidance for acceleration lanes. This paper aims to investigate the actual acceleration characteristics for metered on-ramps with various geometric features and also figure out speed profiles to guide the design of acceleration-lane length. A piecewise-constant acceleration model, which assumes vehicles making uniformly accelerated motion within each short space or time interval, was employed to model vehicle acceleration characteristics. The approach of using distance versus speed profiles for acceleration-length design was also introduced. Results show that acceleration rate at metered on-ramps is not constant; vehicles usually accelerate at a higher acceleration rate when speed is lower and vice versa. It was observed that taper ramps usually produce higher acceleration rates than ramps with an auxiliary lane, and existing acceleration length would also affect drivers' acceleration behavior. Finally, this study pointed out that the acceleration performance data documented in the AASHTO Green Book, which are now widely employed by several state DOTs in the United States as acceleration length design guidance for metered on-ramps, is approximately 1.7 times greater than the value measured at typical taper-type metered on-ramp in California. [ABSTRACT FROM AUTHOR]

No track thermoplastic is a relatively new thermoplastic traffic marking material which can be installed on newly constructed asphalt pavement shortly after finishing paving operations. The main objectives of this study are (1) to develop a test procedure that can be used to determine whether a thermoplastic traffic marking is a no track thermoplastic traffic marking and (2) to run field tests to obtain performance data through real applications of industry-proclaimed no track thermoplastic traffic markings. Sixteen transverse lines were installed in the field for performance evaluation. The research team measured several parameters in the field such as appearance, retroreflectivity, and color. By comparing the testing parameters between no track and regular thermoplastic traffic markings, the research team intended to select a parameter that can be used to develop technical specifications to help decision makers define no track thermoplastic traffic markings. It was found that the best parameters that can be used to define a no track thermoplastic traffic marking were the CIELAB ΔE* value and the CIE94 color tolerance ΔE94*. These two parameters were proposed by the International Commission on Illumination and have been used extensively for measuring color differences. As compared to other testing parameters, the change of these two parameters with time is more consistent and the selected no track thermoplastic traffic markings produced significantly lower ΔE* and ΔE94* values as compared to the regular thermoplastic traffic marking. The research results have the potential to be used by decision makers to develop technical specifications to guide the real engineering applications of no track thermoplastic traffic markings. [ABSTRACT FROM AUTHOR]

This research aims at developing a system of real-time simulation-based dynamic traffic model under mixed traffic flow conditions. The system consists of two layers, namely, simulation layer and real-time control layer. The system is implemented based on rolling horizon approach, which is advanced for each stage; thus real-time data can be incorporated within the framework. In order to predict normative, as well as predictive, information, a simulation-based dynamic traffic assignment model is employed within each stage. Empirical data for a real city network, such as flows from vehicle detectors, are used to validate the model in a real-time environment. The values of mean absolute percentage error and root-mean-squared percentage error are within 15%, and the results show promising agreements between observed and simulated flows. [ABSTRACT FROM AUTHOR]

This paper presents an extensive investigation regarding the impacts of green signal countdown devices (GSCD) on the intersection safety and efficiency, based on field observation of critical driver and vehicle related parameters at two similar intersections (one with GSCD and the other without GSCD) in Shanghai. Statistical analysis results have revealed that the installation of GSCD can (1) encourage drivers to pass the stop-line during the amber time with higher speeds and thus result in better utilization of the amber time and increased capacity of the intersection approach; (2) smooth the driver's response to the phase transition and effectively prevent the sudden change of speeds; (3) effectively eliminate the intersection dilemma zones by allowing the drivers to envision the phase transition and make decisions in advance; and (4) significantly reduce the number of red-light violations. Despite its effectiveness in facilitating the driver decision-making process, the installation of GSCD may adversely increase the possibility of collisions with unexpected crossing vehicles or pedestrians due to the significantly increased speeds of vehicles approaching the amber time. The analysis results from this study will offer the basis for traffic practitioners, researchers, and authorities in China to assess the impact of GSCD with respect to its operational and safety performance, and propose guidelines for its proper field installation. [ABSTRACT FROM AUTHOR]

Decisions regarding the location of motorway interchanges need to be made very carefully because of their economic and political implications. In this paper, we present three optimization models aimed at assisting road administrations when they deal with motorway interchange location problems. The decisions are assumed to be made from the perspective of road users, with the objective of minimizing travel costs. Two of the models are based on existing hub location models, whereas the third one is a new model. The usefulness of the models in real-world situations is illustrated with a case study involving A25, one of the most important Portuguese motorways. When applied to this case study, the new model performed in general clearly better than the other two. [ABSTRACT FROM AUTHOR]

Traffic-responsive plan selection (TRPS) control is one of the largely underutilized control features in National Electircal Manufacturers Association traffic controllers. This control feature allows the controller to change timing plans in arterials or networks in response to changes in traffic patterns automatically, and can therefore result in better performance of the signal system. However, there is limited number of studies that document the procedure of TRPS configuration. The authors have previously published general guidelines on TRPS system setup and configuration, laying out a comprehensive approach that assumes general traffic patterns, a standardized arterial network, and some generic system detector locations. This paper fills a significant gap in literature by providing an illustrative procedure of actual field implementation of a TRPS system in Mexia, Texas. The paper demonstrates the configuration methodology on an arterial network that does not conform to the standardized guidelines. This implementation resulted in up to 75% reduction in delay and up to 33% increase in the lower arterial speed. In this paper, the authors provide some findings and insights into the TRPS configuration process, highlighting some solutions for potential field problems that the engineer might face when configuring a TRPS control system. [ABSTRACT FROM AUTHOR]