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When designing median openings at divided highway intersections, it is important to consider the impacts of simultaneous (noncrossing) left turning movements by vehicles from opposing directions. The AASHTO Green Book recommends minimum lengths of median opening for different design vehicles and median widths. These minimum lengths are calculated based on assumed control radii for left turns from the divided highway into the crossroad and vice versa, and do not account for accommodation of simultaneous left turns. The Green Book minimum median opening lengths can prevent the capability for simultaneous left turns under certain circumstances. This study uses simulated vehicle turning paths to define the minimum conditions for accommodating simultaneous left turns and proposes corresponding revisions to the Green Book guidelines. The new method consists of determining the required control radius as a function of median width and calculating the minimum length of median opening by equations based on geometric relationships. The paper also describes the limitation of the Green Book methodology in addressing median openings with left-turn lanes, which is resolved by application of the proposed method. [ABSTRACT FROM AUTHOR]

The simulation of U-turns is currently of great interest to many transportation professionals due to the widespread use of indirect driveway left-turn treatments. In this study, a procedure was proposed to help transportation professionals model U-turn movements at unsignalized intersections with nontraversable median cross sections in the traffic simulation program VISSIM. The behavioral features of U-turning drivers, such as the priority rule, lane selection, and turning speed of U-turns, were determined using data collected from 13 different locations. A procedure based on a genetic algorithm was proposed to calibrate and validate the VISSIM simulation model. The simulation results of the calibrated VISSIM model were compared to field measured capacity and to the capacity estimated using gap acceptance models developed in previous studies. The calibrated VISSIM simulation model yields mean absolute percent errors of 17.6 and 20.7% for four-lane and six-lane streets, respectively. The results show that VISSIM provides reasonable capacity estimates for U-turns at unsignalized intersections with raised median cross sections, after crucial parameters are properly defined and calibrated. [ABSTRACT FROM AUTHOR]

Sight distance at the intersection of a minor road (controlled by a stop sign) and a major road is an important element of road safety. Several models have been recently developed for the analysis of sight distance at intersections involving horizontal curves on the major road. All these models assume that the intersection lies within the horizontal curve. There are situations, however, when the intersection lies within one of the tangents of the horizontal curve. This case would adversely affect sight distance, especially when the horizontal curve is sharp and the minor road is close to the horizontal curve. This paper develops a new mathematical model for sight distance analysis that explicitly addresses the case where the intersection lies within the tangents of the horizontal curve. The obstruction may be located within the tangent or within the horizontal curve, or located inside or outside of the horizontal curve. Using the model, graphical aids for the required obstruction distances from the major and minor roads, to satisfy sight distance requirements, are developed. The developed model can be used to evaluate sight distance for existing or new intersections. [ABSTRACT FROM AUTHOR]

Traditional pedestrian level of service measures at signalized intersections are based on pedestrian space and pedestrian delay. However, these measures may not adequately reflect the negative impact of right-turning traffic on pedestrians. This paper presents a statistical analysis using a binary logit model that provides new insights into the factors that affect the likelihood that a pedestrian is compromised (delayed, altered their travel path, or altered their travel speed) in response to traffic turning right (on green) during concurrent vehicle/pedestrian signal timing. The statistical analysis indicates that a number of factors affect the likelihood of a pedestrian being compromised including pedestrian direction of travel, right-turn traffic volume, number of pedestrians crossing, whether the pedestrian arrived late and began crossing after the end of the walk interval, and the crosswalk characteristics including location (downtown versus suburban) and one-way/two-way streets. [ABSTRACT FROM AUTHOR]