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The differential per-lane speed limit (DPLSL) is a type of speed control for freeway traffic management in some countries. However, there is no unified standard for the maximum and minimum speed limits for individual lanes. The purpose of this paper is to explore the optimal DPLSL combination scheme on freeways considering safety and efficiency. We simplified the traffic composition to fast and slow vehicles. The slow-start rule was introduced based on the Nagel-Schreckenberg (NaSch) rule and considered the relative speed of adjacent vehicles, acceptable gap, and safety distance to establish lane-changing rules. To reflect the driver's lane change differences, the lane-changing probability of different types of drivers was calibrated by UC-win/road software and driving simulator. In the numerical simulation, six different DPLSL combination schemes were established, and the effects of each speed limit scheme on different traffic flows and different proportions of slow vehicles were separately analysed. The defined safety performance and operation efficiency of traffic flow via the entropy weight method (EWM) were adopted to determine the weight of each index to comprehensively consider various safety and efficiency indexes. The optimal DPLSL combination scheme was obtained through evaluation of the comprehensive indicators. [ABSTRACT FROM AUTHOR]

Crash data in the USA show that approximately 47 percent of fatal crashes occur at night. Sight distance is severely reduced at nighttime as it compares to that in the day often resulting in problematic situations. Horizontal alignment can compound this issue, since most drivers would not be able to see far in advance to recognize the sharpness of the curve and adjust their speed accordingly: a process that they can complete at daylight conditions. This study attempts to understand the influence of roadway geometry and especially curvature on nighttime crashes and presents a preliminary analysis of this issue aiming to identify the magnitude of the problem and provide some guidance for future research. The findings indicate that there is indeed an increased crash occurrence at night and this is related to the curve radius. Sharper curves, i.e., curves with small radii, showed an increase in crashes and crash rate when they were compared to their corresponding daytime crashes. Design consistency was also examined by considering the radii of successive curves. The data again points to the differences in crash experience when considering the relation between two successive curves. Additional work is needed to further explore these issues and develop more statistically robust models for refining the nomographs developed here. [ABSTRACT FROM AUTHOR]

Several factors are usually considered when recommending left-turn phasing at signalized intersections: the volume of through traffic opposing the left-turn maneuvers, the volume of left-turn traffic, the speed of the opposing traffic, sight distance, crash history, and cycle length. The goal of this paper is to find the optimal signal phasing designs that can improve efficiency and safety of the particular signal design in the field in order to test current recommendations and guidelines on left-turn treatments. The researchers assess the impact of the number of rings in a phasing structure, the number of phases and whether to adopt lead or lag phasing on the safety and efficiency of a four-legged signalized intersection. A comprehensive set of 338 signal phasing designs is developed and the impacts are modeled using VISSIM microsimulation. The efficiency of signal phasing sets is evaluated in VISSIM, while the safety aspect is assessed using SSAM software. Optimal scenarios are tested using sensitivity analysis for various traffic flows. The findings show that the current left-turn guidelines may over-protect left-turners which results in reduced efficiency and left-turn delays that can be increased by up to 25%. Revised guidelines should contribute to the decreased delays for left turning vehicles, while keeping the safety standards high. [ABSTRACT FROM AUTHOR]

Roundabouts affect operating speeds depending on a number of parameters. Consequently, their performance affects urban transport systems (safety, environmental and operational impacts) and tools are needed to carry out operating speed predictions. To this end, note that roundabout traffic management and control can be carried out by using road traffic micro-simulation models when a calibration is provided. As a result, the objects of the paper are: i) to use micro-simulation and experimental investigations to analyse operating speed vs. geometry relationship in a roundabout; ii) to calibrate a micro-simulation model; iii) to assess micro-simulation effectiveness in predicting operating speed profiles approaching a roundabout. Driver speed profile was studied and a procedure to predict the operating speed-profile was developed. The data derived from traffic micro-simulation were compared with experimental data. The study permitted to derive several conclusions about operating speed-profiles, micro-simulation effectiveness. Furthermore, it permitted to assess the relevance of a number of parameters in terms of speed prediction and software calibration. [ABSTRACT FROM AUTHOR]