MODELLING THE SURROGATE SAFETY OF VARIOUS LEFT-TURN PHASE SEQUENCES

Left-turns are the most complex maneuvers in a signalized intersection. Based on the flow of the traffic volume through a given intersection, the left-turn phasing may be controlled in various fashions such as: protected only, permissive only, and protected/permissive. Following the introduction of the flashing yellow arrow (FYA) to the 2009 Edition of the Manual on Uniform Traffic Control Devices (MUTCD), many state agencies have implemented these indications for their left-turn permissive movements. Similar to the existing circular green (CG) permissive indication, the FYA requires drivers to yield to oncoming vehicles before making their left-turn. However, given the novelty of these traffic control devices there is a lack of standardization when it comes to the transition between protected and permissive left-turn phasing. A need exists to evaluate the surrogate safety of their implementation through a means of microsimulation evaluation. This research endeavor aims to model various protected-permissive left-turn (PPLT) phase sequences in the FHWA Surrogate Safety Assessment Model (SSAM). Both the FYA and circular green permissive left-turn indications will be implemented in VISSIM microsimulation models. Further, the phase sequencing for each permissive indication will comprise of two sequence options upon transitioning between protected and permissive left-turns; transitioning with and without the all-red clearance interval. Ultimately, this investigation will yield results to develop guidance for practitioners in designing the signal sequencing with PPLT phasing, particularly with the newly introduced FYA traffic control device

All-Red Clearance Intervals for Use in the Left-Turn Application of Flashing Yellow Arrows

With the advancement of implementation for a novel traffic control device, the Flashing Yellow Arrow (FYA), agencies across the country have continually sought strategies to improve intersection operations and safety, specifically with respect to the left-turn application. More so, permissive left-turn intervals have been communicated to drivers using several traffic signal indications; however, most frequently these phases are represented through the circular green (CG) ball and more recently, the FYA. Previous research in this area determined that the FYA indication produced the most effective communication of permissive left-turns. Further, this previous research led to the inclusion of the FYA in the 2009 edition of the Manual on Uniform Traffic Control Devices (MUTCD). In recent years, agencies across the country have embraced the implementation of the FYA for permissive left-turns. However, there remains a lack of national guidance on the definition of change and clearance intervals for transitioning between protected and permissive left-turns. Complicating the matter is the connection between traditional signal phasing/design and human factors. Investigation through driver comprehension and real-world operations will allow us to not only evaluate current conditions, but also experimental and future conditions. Recommendations provided from this research will ultimately offer agencies with the strategies for the most effective transition from a protected left-turn to a permissive left-turn phase

Design of an integrated airframe/propulsion control system architecture

The design of an integrated airframe/propulsion control system architecture is described. The design is based on a prevalidation methodology that uses both reliability and performance. A detailed account is given for the testing associated with a subset of the architecture and concludes with general observations of applying the methodology to the architecture

Dynamic Left-turn Phase Optimization Using Fuzzy Logic Control

The left-turn movement at an intersection has long been a concern of traffic engineers as it is a major capacity reduction factor. Different left-turn signal phasings have been shown to result in significant differences in delay, intersection capacity, and even safety level. First, past studies about leading and lagging signal phases and signal control application are overviewed. Then this research gives a theoretical analysis of signal left-turn phase operations at both isolated and coordinated signalized intersections, compares the difference in delay based on leading and lagging left-turn signal phase designs, analyzes the influences of traffic control delay components for leading and lagging left-turn, identifies the main control factors, and gives a new model to guide the choosing between the leading and lagging left-turn phases. In the third part of this research, some basic mathematical definitions and rules of fuzzy logic control are described. A four-level fuzzy logic control model is designed. To implement this control model, observed approaching traffic flows are used to estimate relative traffic intensities in the competing approaches. These traffic intensities are then used to determine whether a leading or lagging signal phase should be selected or terminated. Finally, this research designs a dynamic traffic signal left-turn phase control system, and implements the four-level fuzzy logic control model to optimize signalized intersection operation. The performance of this dynamic traffic signal left-turn phase fuzzy logic control system compared favorably in all categories to fixed time control, actuated control, and traditional fuzzy control based on simulation using field data. The results suggest that the proposed dynamic traffic signal left-turn phase fuzzy logic control system is a superior and efficient tool for reducing intersection traffic delay. The study also demonstrated that the successful implementation of the proposed model does not rely on the installation of expensive or complicated equipment

Viking '75 spacecraft design and test summary. Volume 3: Engineering test summary

The engineering test program for the lander and the orbiter are presented. The engineering program was developed to achieve confidence that the design was adequate to survive the expected mission environments and to accomplish the mission objective

Manufacturing checkout of orbital operational stages Midterm report, period ending 24 Feb. 1965

Manufacturing checkout of orbital operational Saturn S-IVB stage and instrument unit for parking orbit operation

Development of a New Jughandle Design for Facilitating High-Volume Left Turns and U-Turns

The jughandle is a category of unconventional intersection that redistributes left turns to improve capacity and safety. The New Jersey Department of Transportation, a pioneer in jughandle design, classifies jughandles as either Type A (forward ramp intersecting the cross street), Type B (forward ramp curving left to intersect the mainline), or Type C (reverse loop ramp). This research has developed a new type of jughandle design referred to as Type A+B. This design closes the minor approaches at intersections and directs traffic through a jughandle onto the mainline. It also accommodates U-turns and mainline left turns in a manner similar to traditional Type B jughandles. A unique type of signal phasing, developed to accommodate this design, allows both jughandles to move concurrently. This type of intersection is hypothesized to be most appropriate for the retrofit of suburban arterials requiring installation of a median barrier. The retrofit would install a median barrier with the jughandles, and eliminate signals at intersections with low cross-street volumes, replacing them with right turns followed by U-turns (RTUT). The objective of this research is to determine whether this is an appropriate context for the design, and under what general volume conditions the Type A+B jughandle can reduce delay. Simulation software was used to compare performance measures for the Type A+B jughandle against a conventional intersection and a traditional Type A jughandle, for a wide range of traffic volumes whose turn movement proportions were modeled after a suburban arterial. The research also tested use of this design on an existing suburban arterial in the Pittsburgh region. Measures of performance evaluated include intersection delay, additional footprint, fuel consumption, and number of stops. It was found that the Type A+B jughandle significantly reduced delay under high-volume conditions, and resulted in a much larger intersection footprint

Guidelines for the Installation of Left-Turn Phasing

The objective of this study was to update the guidelines to be considered when determining whether left-turn phasing should be used and the appropriate type at phasing to use. Emphasis was placed on high speed areas. There were 264 intersections included in the study with data obtained tor 518 approaches at these intersections. The data included accidents and characteristics at the intersection. Traffic conflict data were collected. Simulation models were used to estimate delays. Recommendations were made concerning guidelines to consider when deciding whether to install left turn phasing and whether to use protected-only or protected/permitted phasing. Variables considered included accident history, traffic volume and delay, traffic speed, number at left-turn lanes, number of opposing lanes, sight distance, intersection geometrics, left-turn volume, and opposing volume

Improved Safety and Efficiency of Protected/Permitted Right Turns for Bicycles in the Pacific Northwest

DTRT13-G-UTC40Conflict between bicycles and right-turning vehicles on the approaches to intersections is a critical safety concern in urban environments. To understand the safety and operational implications of using protected-permitted right turns (PPRT), a full-scale bicycling simulator experiment was performed. The velocity and lateral position of bicyclists were evaluated during conflicts between bicycles and right-turning vehicles. Two independent variables were analyzed: the signal indication for right-turning vehicles (circular red or green, solid red or green arrow and flashing yellow arrow) and the pavement markings in the conflict area (white lane markings with no supplemental pavement color and white lane markings with solid green pavement applied in the conflict area). Forty-eight participants (24 women and 24 men) completed the experiment. Signal indications and pavement markings had statistically significant effects on bicycle velocity and lateral position, but these effects varied at different levels of the independent variables. Use of PPRT phasing in conjunction with colored pavement markings was associated with increased bicyclist conflict with right-turning vehicles, whereas PPRT phasing with no supplemental colored pavement markings was associated with improved bicyclist safety. The results provide guidance to transportation professionals about how traffic control devices could be applied to conflict areas before signalized intersections

An evaluation of the ATM man/machine interface. Phase 3: Analysis of SL-3 and SL-4 data

The functional adequacy of human factored crew operated systems under operational zero-gravity conditions is considered. Skylab ATM experiment operations generated sufficient telemetry and voice transcript data to support such an assessment effort. Discussions are presented pertaining to the methodology and procedures used to evaluate the hardware, training and directive aspects of Skylab 3 and Skylab 4 manned ATM experiment operations