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In Florida, the increased installation of non-traversable medians and directional median opening has produced an increased number of U-turns on multilane highways. Arguments have been advanced by some opponents of median modification projects that the increased numbers of U-turns may result in safety and operational problems on multilane highways....
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Self-placement in math is becoming increasingly popular in community colleges in the U.S., where students will decide for themselves whether to enroll in non-credit developmental (or remedial) math courses. To fully understand the factors associated with students’ math enrollment choices and the long-term effects of initial math enrollment choices,...
Citations
... This may be due to the fact that "(gap acceptance theory)" has become a simple means of estimating "capacity" in a transport facility. Accepted and rejected gaps are generally thought to be the most important criteria in deciding critical gaps [4]. According to "HCM 2010," the definition of expectations of the most appropriate rejected and smallest approved distance to a given transportation facility can be used to determine the vital headway/gap. ...
... In this definition, Polus (1983) defined "gap" as the time interval between two consecutive cars in the flow of traffic. When merging with the through flow of traffic at median openings, drivers often need bigger distances than when merging with the through flow of traffic at other junction actions [1,2,4]. ...
This study presents the behaviour of vehicles at mid-block median U-turn openings in multi-lane divided urban roads based on gap acceptance in Egypt. Most of the median openings in Egypt are uncontrolled. In this study, models are proposed for calculating U-turn capacity using both field and gap acceptance approaches. This study estimates the critical gap or lag, accepted gaps, and vehicle merging time in U-turn opening. The capacity of median openings mainly depends on the critical gap and follow-up time of U-turn vehicles. Hence, a thorough investigation into the gap acceptance behaviour of U-turn vehicles was carried out. A field approach depends on data collection and was performed on eight different sites in El-Obour and Benha cities in Egypt. Data collection was done during peak hours using a video recording technique at the selected sections. Sections were chosen to be free from gradients, curves, and on-street parking. In addition, Eight factors were considered; five related to the u-turning vehicle (age, gender, vehicle type, queue length, and wait time); three related to the conflicting traffic (gap size, speed, and vehicle type). The results showed that those factors had an effect on the decision in the following descending order: gap size, speed, wait time, conflicting vehicle type, queue time, gender, u-turning vehicle type, and age. The significant factors included gap size and speed. Both field and gap acceptance approaches were used to estimate the capacity of U-turn movement. The field approach was done using regression analysis and investigated to estimate the capacity of U-turn movement. Different factors that might affect the estimated capacity were studied in this approach. Finally, we found that the parameters that affect gap acceptance, including critical gap, move-up time, driver age, and percentage of females, were studied for suitability to be included in the calculation of the capacity model. The method is based on a gap-acceptance approach that was created and refined in Germany. The capacity of each nonpriority stream is calculated using Siegloch's formula.Results from both approaches have been used to derive a regression model to estimate the capacity of U-turn movement at the median opening and calculate the distance between two U-turns for each road.
... In this study at U-turns and intersections the travel time of vehicles were not determined [5]. Statistical approach used for evaluating thecapacity, delay and travel time for U-turn movements concluded simple equations / analysis may not be not correctly evaluate Uturning operational effects of large vehicles of the roadway [6,7]. ...
The operational quality of an urban road system in Pakistan steadily worsens due to increase in traffic volumes and an expectation of higher level of service (LOS). A well-planned, efficient and far-sighted scheme is required to guarantee a safe and smooth operational condition of road system at all times. This study aims to identify the optimization of various parameters such as road geometry, driver behavior, vehicle dimension, vehicle condition and pedestrian to mitigate urban traffic congestion in Peshawar. The aim of this research work is to study the current traffic condition and to model it in a micro simulation software PTV VISSIM.Then appropriately performing calibration and validation of the simulated model for accurate results. To achieve this goal, survey is conducted for micro simulation regarding classified traffic volume, vehicle specifications like its length and width, travel time data, and road geometric data of the research area. Then all the required data is compiled in VISSIM and simulation is run. But initially the results does not replicate the actual field conditions which was checked by statistical approach like paired T-test and Box plot comparison. Then a technique of calibration was performed and then model is validated as well, which gives accurate results for further analysis.
... [32] in the Access Management Manual, approximately 74% of crashes occur at the access points due to the DLT maneuver. Liu [33] evaluated the safety and operational performance impacts for the RTUT maneuvers in Florida. The field measurements were collected from 40 sites in the Tampa Bay metropolitan area. ...
... U-turn studies were performed at directional median openings in Florida. Statistical analysis of U-turn movements for capacity, delay and travel time revealed that U-turning operational effects of large vehicles may not be accurately evaluated from simple equations/analysis [12,13]. ...
Urban traffic congestion is one of the major problems of the developing countries. In routine practice, traffic managers use their knowledge and exposure to address this urban mobility menace. This heuristic approach based on individual experience results in inconsistency causing further delays and an increase in travel time. The aim of this research is to incorporate urban mobility dynamics of the developing countries in a microsimulator for real-time decision making. A pilot-scale research was conducted in Peshawar, one of the ten largest cities of Pakistan. Traffic volume, travel time, vehicle specifications and geometry parameters were determined in the field as input for the microsimulation model. Calibration and validation of the model were done, and results of traffic volume and travel time were compared with actual field data and statistical similarity confirmed through paired t-test. The analysis of queue delay, travel time and traffic flow indicates that in most of the cases congestion was found near the intersections and U-turns which was verified from the field data as well. The options of a roundabout and a flyover were assumed in the analysis; resultant queue delay and travel time decreased. With the provision of the roundabout and flyover, the capacity of traffic flow was also improved.
... Assertions from earlier studies indicated that most traffic conflicts at unsignalized intersections are due to left turn. Left turn in unsignalized intersections, especially from minor street to major street creates many problems and increases conflicts, which is a great factor for accidents [9]. This situation may create many problems and increased conflicts, which could be a great factor for a serious or fatal accidents at the intersection. ...
The counting of traffic conflict allows the estimation of accident potential at a particular location such as at-grade intersection. The objective of this paper is to examine the evasive action of driver occurs with some frequency at Shao intersection which may result in potential accident. This paper applied traffic conflict techniques to evaluate collision potential at unsignalized intersection located at Shao. The morning and evening peak traffic flow was captured using a video camera for seven days and then analyzed by playing back the video on daily basis. The 100 sample size of observed conflict was based on 95% confidence level, 5% permitted error and the proportion of the vehicles that were involved in a specific conflict for the observed traffic flow. The conflicts identified were compared with volume counts at minor approach. The daily peak hour approach traffic volumes were found to have a close relationship with the percentage values of conflict on the two minor approaches. It also showed that rear end collision accounted for more than 70 percent of traffic conflicts and it correlated well with the traffic volumes on WB and EB approaches.
... The purpose of using non-traversable and directional median openings is to eliminate problems associated with left-turns and crossing movements on multilane highways (Liu, 2006). As a result of this design decision, drivers desiring to make direct left-turns at a driveway will be relocated to a downstream U-turn bay to make U-turns. ...
... Moreover, one of iterations to improve the performance of intersections is by diverting left turning flow from crossing through traffic the main intersection. This will reduce the number of signal phases (Liu, 2006). ...
Abstract Field observations indicate that left turning vehicles at U-turn sections lead to a
significantly bottleneck (congestion) at both origin and destination (opposing) roads. The
bottlenecks have been observed in several U-turns such as Kufa–Najaf U-turn sections,
Najaf–Karbala U-turn sections. It was found that left turn flow from U-turn leads to high
congestion on both origin and destination roads. Therefore, field improvements have been
done by the traffic policemen who create a temporary barrier from traffic plastic signs in
... During the recent era there has increased installation of unsignalized median openings to accommodate these illegal U-turns in most of the Indian states. This increased installation reflects the much needed attention towards Access Management [1,2]. One of the best ways of accessing roads is by installing non-traversable and un-signalized median openings [2,3]. ...
... This increased installation reflects the much needed attention towards Access Management [1,2]. One of the best ways of accessing roads is by installing non-traversable and un-signalized median openings [2,3]. The purpose of using non-traversable and directional median openings is to eliminate problems associated with left-turns and crossing movements at intersections on multi-lane highways [1,2,3]. ...
... One of the best ways of accessing roads is by installing non-traversable and un-signalized median openings [2,3]. The purpose of using non-traversable and directional median openings is to eliminate problems associated with left-turns and crossing movements at intersections on multi-lane highways [1,2,3]. At un-signalized median openings vehicular interactions are extremely complex [3,4]. ...
Over the past few years there has been increased installation of non-traversable un-signalized median openings in most of the urban regions in India. The motive behind this installation is to eliminate problems associated with illegal U-turns at intersections and other traffic facilities close to the median openings on multi-lane urban roads. Data collected for this study is in the form of video-images of six U-turn median openings on 4-lane and 6-lane roads situated in the cities of Bhubaneshwar, Rourkela and Ranchi located in the eastern part of India. This paper introduces a new concept on merging behavior of U-turn vehicles for evaluation of gaps accepted by drivers at median openings based on the "INAFOGA" method; which is further compared with the critical gap values obtained by and Macroscopic Probability Equilibrium concept for heterogeneous traffic flow in the urban region of the Indian states. IBM-SPSS 22.0 has been used to perform a paired-sample Hypothesis (t-test) between these two methods which reveal that critical gap values obtained by "INAFOGA" are 18-31% more than those obtained by Probability Equilibrium method. Radar plots, box-plots, t-statistic, two-tailed significance value coupled with higher critical gap values for different modes of transport (except Sport Utility Vehicles) validates the fact that "INAFOGA" method is indeed appropriate under mixed traffic conditions. This observation on influence area of gap acceptance at median openings using the merging behavior concept has given sufficient clue to carry out further research on critical gaps at roundabouts or interchanges.
... Safety at the median openings is usually improved by controlling the number of movements that use the openings. For example Florida-as reported by Liu (2006) and ...
... Yang (2001) Although Liu (2006) demonstrated that the separation between upstream driveways and downstream U-turn median openings affects both safety and operations, in the end recommended that only safety criteria should be used in determining the separation. Liu did not clarify why the 50 th percentile was taken as the threshold value instead of lower percentiles which correspond to lower crash rash rates. ...
... A study similar to Liu's (2006) study was conducted to determine minimum separation of upstream driveways and downstream U-turn median openings (Pirinccioglu, 2007). The study used rates of conflicts (evasive actions for crash avoidance) as surrogate for safety. ...
The time span of a vehicle making turns, which is from the time a turn starts to the time the turn ends, are the basis of determination of essential data of vehicle motion like slip angles, forces on tires, except the vehicle is in an ideal one-dimensional motion. When the road condition is sensed by sensors on vehicle’s driver assistance systems, how to take a turn is the next step that should be calculated. After the turn starts, the end time of the turn should be adjusted in real time to remedy the imperfection digital simulation of the road sensed by the sensors. This paper compares two turning models and proposes an algorithm to adjust the end time of the turning time span during the turning motion of the vehicle. Subsequently, the algorithm is applied to two classic models of car, BMW M3 and Chevrolet Cavalier in four common motions: U-turn, lane change, sharp U-turn and sharp lane change. The algorithm proposed can be applied to every scenario that should take use of the turning time length, including the mathematical model of crossings, traffic flow of rush hours, or simply estimate the time span in unmanned vehicle control systems.
Previous research has shown that vehicles making U-turns at a signal-controlled urban road junction can negatively affect the performance of the junction. This paper reports on a study carried out to determine a suitable position to allow U-turns at signalised intersections in Tehran, Iran, based on their effects on network travel time. A section of the traffic network of Tehran was modelled using specialist software. To make the results more realistic, local traffic and driver behavioural parameters were calibrated and fed into the software. Various scenarios with different intervals were developed, with ten median openings before a signal-controlled junction and ten median openings after the junction. The results indicate that if the median opening for conducting U-turns is located 190 m before the junction, the network delay is lower than the other scenarios considered.
