• International Journal of Highway Engineering
• /
• v.14 no.2
• /
• pp.83-91
• /
• 2012

This study deals with the operational efficiency of roundabout. The roundabouts generally have such the merits as high capacity, delay reduction, safety improvement, and others. Circular intersection can be divided into the rotary and roundabout according to travelling priority. The objective of this study is to comparatively analyze the operational efficiency of rotary and roundabout by scenario. In pursuing the above, this study gives the particular attentions to developing 256 scenarios according to the directional and entering traffic volume and analyzing the delay using VISSIM. The main results are as follows. First, the average delay of rotary was analyzed to be 1.56-8.74 times of roundabout. Second, the operational efficiencies of rotary and roundabout were analyzed to be better in the case of bigger differences in the traffic volumes between the main and minor roads. Third, the average delay of the 4-legged was evaluated to be 1.77-11.70 times of 3-legged intersection. Finally, 2-lane intersection (3-legged & 4-legged) was analyzed to be 2.02-2.23 times of 1-lane intersection.

• Journal of Navigation and Port Research
• /
• v.27 no.4
• /
• pp.471-478
• /
• 2003

In the Signalized Intersection, the capacity analysis is conducted with a large amount of input data such as road way, traffic and signal condition. but the level of service(LOS) is determined by delay estimated as a measure of effectiveness (MOE) based on this procedure. However, It is under the circumstances which are not considered for the errors caused by the uncertainty of input data in the field(the turing volumes, lane geometry, signal timing, grade of approach lane, percentage heavy vehicles, peak hour factor and arrival type etc.) as become the bases in the determination of the capacity and LOS. It includes the problem of reliability which is not verified for the capacity and LOS estimated. So, this study is to suggest the minimization of their influences by examining whether the uncertainty of input data such as the traffic volume, percentage of heavy vehicles and roadway geometry on the approach lane in the intersection under the study affects the capacity analysis and LOS determination.

• Journal of Korean Society of Transportation
• /
• v.27 no.1
• /
• pp.157-167
• /
• 2009

This study deals with the turn penalty functions in the urban transportation demand forecasting. The objectives are to develop the penalty functions of left-turn traffic in the case of signalized intersections, and to analyze the applicability of the functions to the traffic assignment models. This is based on the background that the existing models can not effectively account for the delays of left-turn traffic which is bigger than that of through traffic. In pursuing the above, this study gives particular attention to developing the penalty functions based on the degrees of saturation by simulation results of Transyt-7F, and analyzing the applicability of the functions by the case study of Cheongju. The major findings are the followings. First, two penalty functions developed according to the degrees of saturation, are evaluated to be all statistically significant. Second, the results that the above functions apply to the Cheongju network, are analyzed to be converging, though the iteration numbers increase. Third, the link volumes forecasted by turn penalty functions are evaluated to be better fitted to the observed data than those by the existing models. Finally, the differences of traffic volumes assigned by two functions, which are exponential and divided forms, are analyzed to be very small.

• Journal of Korean Society of Transportation
• /
• v.27 no.1
• /
• pp.53-62
• /
• 2009

The purposes of the study is to comparatively analyze the applicability of roundabout to the diamond interchange. In pursuing the above, this study give the particular attentions to comparing the performances of roundabout with those of TWSC and signalized intersection based on the aaSIDRA software. The main study results are as follows. First, when the entering traffic volumes(ETV) are more than 480pcph, the single-lane roundabout is analyzed to be more effective than 4-leged unsignalized intersection and when ETV are $480{\sim}1,880pcph$, double-lane roundabout is analyzed to be more effective than 4-legged intersection Second, when ETV are more than 980pcph at the single-lane intersection and $1,600{\sim}3,680pcph$ at the double-lane intersection, roundabout is analyzed to be more effective than other 3-legged intersections. In summary, when the roundabout installs at the interchange, it is important to consider the range of ETV.

• KSCE Journal of Civil and Environmental Engineering Research
• /
• v.35 no.5
• /
• pp.1111-1121
• /
• 2015

Roundabouts face a congestion problem when there are unbalanced traffic conditions, especially during peak times. The congestion at roundabouts results in long delay times and low level of service. Some research has addressed congestion problems of the metering roundabout, however, few studies have focused on the congestion issues of the double signals metering roundabout. This research bridges this gap through analyzing the congestion issues of the Old Belair double signals roundabout in Adelaide. The research proposes a new analysis method based on a four-nodes intersection in order for double signals roundabout analysis to be carried out as follows: firstly, at the modeling stage, a connection of four individual intersections, adjustment of lane geometry, input of directional traffic volumes, priority and phase time set up are proposed. Secondly, for calibration, PFF, critical gap, follow-up headway and extra bunching values have been applied. The results from the analysis show that the new method is able to analyze the delay time, level of service, degree of saturation and allow for further analysis.

• The Journal of The Korea Institute of Intelligent Transport Systems
• /
• v.18 no.2
• /
• pp.77-92
• /
• 2019

TPCLT is a advanced signal system that serves twice left turn phases during the same cycle. TPCLT can be a useful where the left turn traffic volume is high and the length of the left turn lane is short. This study examined the effectiveness of TPCLT in reducing delay for a signalized three-Leg intersection and proposed the application of TPCLT signal system. 108 scenarios with different traffic volumes were created. This study analyzed the control delay of the three-Leg intersection in case TPCLT is operated and non-TPCLT is operated. As a result of analysis, it was shown that TPCLT was effective in most of the scenarios. When traffic volume ratio of the left turn is 30~40%, TPCLT was more effective at reducing the control delay. The study result shows significant delay reduction for the left turning traffic and it is approximately 50 seconds. The opposing movement's average control delay increased 2 seconds. The effect of TPCLT on the length of left turn lane was analyzed. As a result, it is found that TPCLT is effective when the length of left turn lane is 30%~60% compared to that of conventional three leg intersection operations.

• International Journal of Highway Engineering
• /
• v.15 no.3
• /
• pp.177-189
• /
• 2013

PURPOSES: This study aims to suggest a proper left-turn treatment method for the bicycle traffic flow at four-legged intersections. METHODS: Four types of crossing methods are proposed and analyzed : (1) indirect left turn, (2) direct left turn, (3) direct left turn on a Bike Box, and (4) direct left turn on bike left turn lane. The VISSIM simulation tests were conducted based on forty-eight operation scenarios prepared by varying vehicle and bicycle traffic volumes. RESULTS : The results from the four-legged signalized intersections suggest that (1) the indirect left turn is appropriate when vehicle demand is high, (2) the direct left turn is efficient on most traffic situation but the safety is a concern, (3) the direct left turn on a Bike Box is appropriate when bicycle demand is high while vehicle demand is not, and (4) the direct left turn on a bike left turn lane is appropriate when both vehicle and bicycle demand are low. CONCLUSIONS : The direct left turn of bicycle provides more efficiency than the indirect left turn at the four-legged intersections but to apply the methods and to study more, advanced evaluation methods, related law, and insurance programs are needed.

• Journal of Korean Society of Transportation
• /
• v.25 no.6
• /
• pp.55-63
• /
• 2007

This research deals with the relations between intersection types and traffic accidents in the case of Korean expressways. The purpose of this research is to test the hypotheses that traffic accidents depend on intersection types and geometric design elements. The main research results are as follows. First, the accident comparisons that are drawn from junctions with interchanges, and trumpet interchanges with other types of interchanges respectively displays no significant meaning. However, the differences among four types of trumpet interchanges are found to be meaningful. In other words, the BO type trumpet interchanges seem to have far more traffic accidents than other types of trumpet interchanges. Second, hypothesis tests show that approximately 90 degree and one lane connection roads have lower accident rates. Based on this research, the following directions can be suggested for the safer types of intersections and geometric design elements in freeway construction. From a road safety point of view, it is advisable not to introduce BO type interchanges. It is also desirable that the intersection angle should be approximately 90 degrees. Furthermore, it would be wise to design one lane roads if the connection road has low traffic volumes.

• Proceedings of the KOR-KST Conference
• /
• 1995.02a
• /
• pp.3-32
• /
• 1995

The Highway Capacity Manual specifies procedures for evaluating intersection performance in terms of delay per vehicle. What is lacking in the current methodology is a comparable quantitative procedure for ass~ssing the safety-based level of service provided to motorists. The objective of the research described herein was to develop a computational procedure for evaluating the safety-based level of service of signalized intersections based on the relative hazard of alternative intersection designs and signal timing plans. Conflict opportunity models were developed for those crossing, diverging, and stopping maneuvers which are associated with left-turn and rear-end accidents. Safety¬based level-of-service criteria were then developed based on the distribution of conflict opportunities computed from the developed models. A case study evaluation of the level of service analysis methodology revealed that the developed safety-based criteria were not as sensitive to changes in prevailing traffic, roadway, and signal timing conditions as the traditional delay-based measure. However, the methodology did permit a quantitative assessment of the trade-off between delay reduction and safety improvement. The Highway Capacity Manual (HCM) specifies procedures for evaluating intersection performance in terms of a wide variety of prevailing conditions such as traffic composition, intersection geometry, traffic volumes, and signal timing (1). At the present time, however, performance is only measured in terms of delay per vehicle. This is a parameter which is widely accepted as a meaningful and useful indicator of the efficiency with which an intersection is serving traffic needs. What is lacking in the current methodology is a comparable quantitative procedure for assessing the safety-based level of service provided to motorists. For example, it is well¬known that the change from permissive to protected left-turn phasing can reduce left-turn accident frequency. However, the HCM only permits a quantitative assessment of the impact of this alternative phasing arrangement on vehicle delay. It is left to the engineer or planner to subjectively judge the level of safety benefits, and to evaluate the trade-off between the efficiency and safety consequences of the alternative phasing plans. Numerous examples of other geometric design and signal timing improvements could also be given. At present, the principal methods available to the practitioner for evaluating the relative safety at signalized intersections are: a) the application of engineering judgement, b) accident analyses, and c) traffic conflicts analysis. Reliance on engineering judgement has obvious limitations, especially when placed in the context of the elaborate HCM procedures for calculating delay. Accident analyses generally require some type of before-after comparison, either for the case study intersection or for a large set of similar intersections. In e.ither situation, there are problems associated with compensating for regression-to-the-mean phenomena (2), as well as obtaining an adequate sample size. Research has also pointed to potential bias caused by the way in which exposure to accidents is measured (3, 4). Because of the problems associated with traditional accident analyses, some have promoted the use of tqe traffic conflicts technique (5). However, this procedure also has shortcomings in that it.requires extensive field data collection and trained observers to identify the different types of conflicts occurring in the field. The objective of the research described herein was to develop a computational procedure for evaluating the safety-based level of service of signalized intersections that would be compatible and consistent with that presently found in the HCM for evaluating efficiency-based level of service as measured by delay per vehicle (6). The intent was not to develop a new set of accident prediction models, but to design a methodology to quantitatively predict the relative hazard of alternative intersection designs and signal timing plans.

• The Journal of The Korea Institute of Intelligent Transport Systems
• /
• v.10 no.6
• /
• pp.24-31
• /
• 2011

This study deals with the operational effectiveness of roundabout. The roundabout is currently under consideration in our country depending on the result of existing researches, that the roundabout decreases delay and is environmentally friendly compared to the signalized intersection. The purpose of the study is to analyze the operational effectiveness of the roundabout by the change of pedestrian traffic volume. In pursing the above, this study gave particular emphasis to designing a network of roundabout, developing some scenarios for analysis including both entering traffic volume and pedestrians volume, and comparatively analyzing the average controlled delay time per vehicle. In this study, VISSIM model was used as a tool for traffic simulation. The main results are as follows. First, as a result of analyzing a traffic delay based on the pedestrian traffic volume, pedestrian traffic volume was analyzed to have a great impact on the roundabout operation. Second, the more pedestrian traffic volume were evaluated to indicate the more traffic delay. When the entering volumes with 1,000persons/hour (pedestrian volume) were more than 800pcph in the single-lane and 1,600pcph in the double-lane roundabout, the operational efficiencies of signalized intersections were evaluated to be better than those of roundabouts.