Journal of Transportation Engineering, Part A: Systems

The study investigated the analysis of nonstrict priority left-turning vehicle maneuvers with a permitted phase at signalized intersections, based on field observation at four sites (one with a permitted phase and the others with protected phases) in Changchun, China. Trajectory densities at four cross sections along the turning paths were collected, and the concept of a left-turn group was proposed for discussing the maneuver. Then, analysis was conducted by means of clustering and probability distribution fitting. The results revealed that (1) a significantly wider trajectory distribution appears in permitted left-turning maneuvers than in protected phases; (2) four different maneuvers exist for the leading vehicle of a left-turn group; and (3) following time intervals in a left-turn group have a leptokurtic distribution that can be best fitted by the log-logistic and lognormal models. This study provides a better understanding of the nonstrict priority left-turning maneuver with a permitted phase with respect to operational performance, and offers the basis for further study on permitted left-turning streams, such as their capacity and delay.

This work provides a practical approach for the definition of rural road networks in hilly regions of developing countries. The proposed methodology enables the determination of obligatory points for the road network, which provides basic accessibility to settlements within a specified maximum walking time. The proposed methodology, based on a geographic information system (GIS), takes into account the regions’ main characteristics (i.e., trails slope and availability), and does not require significant data. Moreover, simplifications to the method are proposed herein, allowing it to be used even without a GIS; thus making it a more practical, realistic, and user-friendly approach for obtaining real-world road networks of hilly regions in developing countries.

The Gipps-type models have been utilized in vehicle-following studies. These models are significant in practice and benefit intelligent transportation systems. However, they have received little attention in the literature. The aim of this article is to develop and improve Gipps-type vehicle-following models. The shortcomings of Gipps-type models are addressed, and three models are consequently developed and evaluated through a case study. The proposed models adopt a nonlinear braking rate instead of a linear function and involve the second leading vehicle in model formulation. The velocity and travel distance of the subject vehicle are simulated to measure the performance of models in a macroscopic perspective.

At coordinated intersections, when the side-street required green time is less than the required pedestrian time (RPT) to cross the main street, there are two options to consider when implementing RPT into side-street green time. One option is to add RPT to the side street at all cycles whether or not there is a pedestrian call. This method is sometimes referred to as accommodation (A) of RPT. With this method, the signal remains coordinated at all times with side-street green time even when that much green time is not needed. Another option is to extend the side-street green time interval only when it is required, that is, when there is a pedestrian call to cross the main street, and brings the signal into coordination by one of the transition methods. This method is called nonaccommodation (NA) in this paper. It keeps side-street green time to its minimum required green time at the expense of disturbing coordination when there is a pedestrian call. The optimum method depends on several factors including cycle length, vehicle and pedestrian volume, the value of RPT compared with required side-street green time, transition method, and other signal parameters. This research provides a guideline to determine when accommodation (A) is preferable over NA under each condition. In cases where the cycle length is not long enough to accommodate RPT into side-street green time without extending it, a threshold for pedestrian volume is provided. If pedestrian volume is higher than this threshold, pedestrian timing will be accommodated. If pedestrian volume does not warrant accommodation, practitioners can use several graphs, which are extracted from simulation to determine the optimum method for a wide range of conditions. To provide these graphs, 7,776 scenarios were simulated for both A and NA methods, forming a total of 15,552 cases. Then, at the end, the guideline is tested on one intersection.

Use of speed-prediction models sometimes appears as a feasible alternative to laborious field measurements, particularly when field data cannot fulfill designers’ requirements. However, developing speed models is a challenging task, especially in the context of developing countries like India where vehicles with diverse static and dynamic characteristics use the same right of way. Here, the traffic composition plays a significant role in determining vehicular speed. Determination of passenger car units (PCU), which is required to convert heterogeneous traffic flow to its homogeneous equivalent, also requires speed of different types of vehicles at varying traffic conditions and traffic volumes on the road. In this context, the present research is carried out to examine the effects of traffic volume and its composition on speed and PCU factors for individual types of vehicles under mixed traffic conditions. Classified traffic-volume and speed data were collected at six-lane divided arterial sections in New Delhi and categorized speed models developed adopting a kriging approximation technique, an alternative for commonly used regression. A novel algorithm for selecting the optimal correlation function in kriging has also been proposed in this paper. Developed speed models are validated with the data set of another location kept aside for this purpose, and the predicted speeds show a good agreement to the observed ones. Predicted speeds are then used to estimate PCU factors for each vehicle category. Finally, the proposed models are utilized to evaluate the effects of traffic volume and its composition on speed and PCU of different vehicle categories.

The highway capacity manual (HCM) is the publication used most often to estimate capacity. Field measurements in previous research have shown that the capacities at several freeway bottlenecks are noticeably lower than the values recommended in the HCM (highway capacity manual), by an order of a few hundred vehicles per lane. In addition, several articles have shown that maximum freeway throughput may differ between undersaturated and oversaturated conditions. This paper assembles capacity flows before and after the initiation of oversaturation, discusses recommended definitions of capacity, and provides capacity values and capacity prediction models for various types of freeway segments. It is recommended to define prebreakdown capacity as the 85th percentile of the 15-min average prebreakdown flow and the postbreakdown capacity as the 85th percentile of the 15-min average discharge flow. A clear drop in throughput between prebreakdown and discharge capacity values was observed. The paper concludes by providing recommended capacity values as a function of the number of lanes and the segment type. These values are significantly lower than those recommended in the HCM (highway capacity manual) for basic freeway segments.