scholarly journals An Analysis of the Interactions between Adjustment Factors of Saturation Flow Rates at Signalized Intersections

2020 ◽  
Vol 12 (2) ◽  
pp. 665 ◽  
Author(s):  
Yi Wang ◽  
Jian Rong ◽  
Chenjing Zhou ◽  
Xin Chang ◽  
Siyang Liu
Keyword(s):  
Traffic Congestion ◽  
National Standard ◽  
Percentage Error ◽  
Heavy Vehicles ◽  
Highway Capacity ◽  
Left Turn ◽  
Highway Capacity Manual ◽  
Lane Width ◽  
Adjustment Factors ◽  
Saturation Flow

An insufficient functional relationship between adjustment factors and saturation flow rate (SFR) in the U.S. Highway Capacity Manual (HCM) method increases an additional prediction bias. The error of SFR predictions can reach 8–10%. To solve this problem, this paper proposes a comprehensive adjusted method that considers the effects of interactions between factors. Based on the data from 35 through lanes in Beijing and 25 shared through and left-turn lanes in Washington, DC, the interactions between lane width and percentage of heavy vehicles and proportion of left-turning vehicles were analyzed. Two comprehensive adjustment factor models were established and tested. The mean absolute percentage error (MAPE) of model 1 (considering the interaction between lane width and percentage of heavy vehicles) was 4.89% smaller than the MAPE of Chinese National Standard method (Standard Number is GB50647) at 13.64%. The MAPE of model 2 (considering the interaction between lane width and proportion of left-turning vehicles was 33.16% smaller than the MAPE of HCM method at 14.56%. This method could improve the accuracy of SFR prediction, provide support for traffic operation measures, alleviate the traffic congestion, and improve sustainable development of cities.

Evaluating the Operational Effect of Narrow Lanes and Shoulders for the Highway Capacity Manual

2019 ◽  
Vol 2673 (10) ◽  
pp. 558-570 ◽  
Author(s):  
Alexandra Kondyli ◽  
David K. Hale ◽  
Mohamadamin Asgharzadeh ◽  
Bastian Schroeder ◽  
Anxi Jia ◽  
...  
Keyword(s):  
Traffic Congestion ◽  
Flow Speed ◽  
Mitigation Strategies ◽  
Analytical Models ◽  
Highway Capacity ◽  
Highway Capacity Manual ◽  
Lane Width ◽  
Adjustment Factors ◽  
Manual Methods ◽  
Width Reduction

Unnecessary traffic delays and vehicle emissions have adverse effects on quality of life. To solve the traffic congestion problem in the U.S.A., mitigation or elimination of bottlenecks is a top priority. Agencies across the U.S.A. have deployed several congestion mitigation strategies, such as lane and shoulder width reduction, which aim to adding lanes without significantly altering the footprint of the freeway. A limited number of studies have evaluated the operational benefits of lane narrowing. Although the Highway Capacity Manual does account for lane and shoulder widths, the adjustments that it provides are outdated. The goal of this research was to develop analytical models, compatible with the Highway Capacity Manual methods, to account for lane and shoulder width narrowing, using field data from across the U.S.A. This paper presents a new free-flow speed regression model, which accounts for lane and shoulder widths, and capacity adjustment factors depending on the lane width.

scholarly journals Determination of Level of Service (LOS) on Different Roads in Kuching Area (A Case study)

2009 ◽  
Vol 1 (1) ◽  
pp. 1-6
Author(s):  
Chen K.C. ◽  
Larry S.T.
Keyword(s):  
Traffic Congestion ◽  
Urban Areas ◽  
Qualitative Assessment ◽  
Level Of Service ◽  
Heavy Vehicles ◽  
Traffic Light ◽  
Highway Capacity ◽  
Highway Capacity Manual ◽  
Lane Width ◽  
Traffic Composition

The concept of Level of Service (LOS) is originated from the Highway Capacity Manual (HCM). LOS is a qualitative assessment of the operational performance of a roadway facility based on quantitative performance measures. Many transportation infrastructure funding decisions are based on LOS analysis, and LOS designations are intended to represent user-perceived quality of service. This study has been carried out to determine the LOS on different roads. The profile of study area is in Kuching, Sarawak where five roads with different characteristics and posted speed of urban multilane with 80km/hr and 70km/hr, suburban two-lane two-way with 90 km/hr and 80km/hr had been selected for the studies. Substantial numbers of inputs are required for the LOS analysis and determination based on HCM procedures. These inputs are: a long list of traffic volume collected in different peak hours; traffic composition such as proportion of heavy vehicles in traffic; geometric characteristics such as number of lanes, lane width, shoulder width, and approach grades. Results of the study showed that LOS in the urban multilane is still in satisfactory range with LOS ranging from C to D except for most of the traffic congestion cases in urban multilane at the traffic light junctions and roundabouts. However, LOS in the suburban two-lane two-way is only satisfying in the range of LOS E; hence multilane should be introduced in such cases. Recommendations such as to provide various or multitude modes of transportation needs should be introduced in urban area. Furthermore, a suitable and efficient hierarchy in road system should be provided in suburban areas before turning into urban areas.

scholarly journals Effect of U-Turns and Heavy Vehicles on the Saturation Flow Rates of Left-Turn Lanes at Signalized Intersections

2020 ◽  
Vol 12 (11) ◽  
pp. 4485
Author(s):  
Abdelrahman Abuhijleh ◽  
Charitha Dias ◽  
Wael Alhajyaseen ◽  
Deepti Muley
Keyword(s):  
Flow Rate ◽  
Signalized Intersections ◽  
The State ◽  
Heavy Vehicles ◽  
Flow Rates ◽  
Left Turn ◽  
Highway Capacity Manual ◽  
Adjustment Factors ◽  
Saturation Flow Rate ◽  
Saturation Flow

The Saturation Flow Rate (SFR) is a primary measure that can be used when estimating intersection capacity. Further, the efficiency of signal control parameters also depends on the accuracy of assumed SFR values. Driver behavior, type of movement, vehicle type, intersection layout, and other factors may have a significant impact on the saturation flow rate. Thus, it is expected that driving environments that have heterogeneous driver populations with different driving habits and cultures may have different SFRs. In practice, the proposed SFRs based on US standards (Highway Capacity Manual, 2016) have been adopted in the State of Qatar without validation or calibration to consider the local road environment and the characteristics of the driving population. This study aims to empirically analyze the saturation flow rates for exclusive left-turn lanes and shared left- and U-turn lanes at two signalized intersections in Doha city, while considering the effects of heavy vehicles and U-turn maneuvers. Empirical observations revealed that the average base SFR, i.e., when the influences from heavy vehicles and U-turns were excluded, could vary approximately from 1800 vehicles per hour per lane (vphpl) to 2100 vphpl for exclusive left-turning lanes and approximately from 1800 vphpl to 1900 vphpl for shared left- and U-turning lanes. Furthermore, this study proposed different adjustment factors for heavy vehicle and U-turn percentages which can be applied in practice in designing signalized intersections, particularly in the State of Qatar.

Estimating Intersection Approach Delay Using 1985 and 1994 Highway Capacity Manual Procedures

1996 ◽  
Vol 1555 (1) ◽  
pp. 23-32
Author(s):  
Stephen M. Braun ◽  
John N. Ivan
Keyword(s):  
Field Measurements ◽  
Signalized Intersections ◽  
New Technique ◽  
Adjustment Factor ◽  
Highway Capacity ◽  
Flow Rates ◽  
Left Turn ◽  
Highway Capacity Manual ◽  
A New Technique ◽  
Saturation Flow

The current methods for determining average stopped delay at signalized intersections were studied. Field measurements of average stopped delay were obtained and compared with values computed using both the 1985 and 1994 editions of the Highway Capacity Manual (HCM). The 1994 HCM uses an equation to predict the progression adjustment factor (PF), a new technique for determining the left-turn adjustment factor for saturation flow rates, and a new set of equations for determining the uniform delay parameter for left-turn lane groups with primary and secondary phasing. Overall, the 1994 HCM produces better estimates of intersection stopped delay than the 1985 HCM.

Effect of Lane Width on Speeds of Cars and Heavy Vehicles in Work Zones

2005 ◽  
Vol 1920 (1) ◽  
pp. 41-48 ◽  
Author(s):  
Madhav V. Chitturi ◽  
Rahim F. Benekohal
Keyword(s):  
Flow Speed ◽  
Heavy Vehicles ◽  
Work Zones ◽  
Passenger Cars ◽  
Highway Capacity ◽  
Speed Reduction ◽  
Interstate Highways ◽  
Highway Capacity Manual ◽  
Traffic Stream ◽  
Lane Width

Traffic data were collected from 11 work zones on Interstate highways in Illinois in which one of the two lanes was open. The reductions in free-flow speed (FFS) due to narrow lanes and lateral clearances in work zones were studied. It was found that the reductions in FFSs of vehicles in work zones because of narrow lanes were higher than the reductions given in the Highway Capacity Manual for basic freeway sections. The data also showed that the narrower the lane was, the greater the speed reduction was. The data showed that the FFSs of heavy vehicles were statistically lower than the FFSs of passenger cars, even though the speed limit was the same for both types of vehicles. In addition, the reduction in the FFSs of heavy vehicles was greater than the reduction in the FFSs of passenger cars. This greater reduction in the speed of heavy vehicles affected the performance of the traffic stream in work zones. Thus, it should be considered in the computation of the passenger car equivalence for heavy vehicles. It is recommended that 10, 7, 4.4, and 2.1 mph be used for speed reduction in work zones for lane widths of 10, 10.5, 11, and 11.5 ft, respectively.

Effects of U-Turns on Capacities of Signalized Intersections

2005 ◽  
Vol 1920 (1) ◽  
pp. 74-80 ◽  
Author(s):  
Pan Liu ◽  
Jian John Lu ◽  
Jingjing Fan ◽  
Juan C. Pernia ◽  
Gary Sokolow
Keyword(s):  
Regression Model ◽  
Signalized Intersections ◽  
Signalized Intersection ◽  
Left Turn ◽  
Highway Capacity Manual ◽  
Bay Area ◽  
Study Team ◽  
Adjustment Factors ◽  
Left Turns ◽  
Saturation Flow

In Florida, the increased use of restrictive medians and directional median openings has generated many U-turns at signalized intersections. There is no widely accepted procedure for estimating the effects of U-turning vehicles on signalized intersection capacity. In the 2000 edition of the Highway Capacity Manual, U-turns are treated as left turns for estimation of saturation flow rates. However, the operational effects of U-turns and left turns are different. This study analyzed the effects of U-turning vehicles on the left-turn saturation flow rate. Data were collected at three signalized intersections in the Tampa Bay area in Florida. In total, the study team recorded the queue discharge times for 260 queues, including 571 U-turning vehicles and 1,441 left-turning vehicles. On the basis of the data collected in the field, a regression model was developed to estimate the relationship between the average queue discharge time for each turning vehicle and the various percentages of U-turning vehicles in the left-turn traffic stream. Adjustment factors for various percentages of U-turning vehicles were also developed by using the regression model. The adjustment factors developed in this study can be directly used to estimate the capacity reduction due to the presence of various percentages of U-turning vehicles at a signalized intersection.

Effect of Pedestrians on Capacity of Signalized Intersections

1998 ◽  
Vol 1646 (1) ◽  
pp. 37-46 ◽  
Author(s):  
Joseph S. Milazzo ◽  
Nagui M. Rouphail ◽  
Joseph E. Hummer ◽  
D. Patrick Allen
Keyword(s):  
Signalized Intersections ◽  
Geometric Constraints ◽  
Highway Capacity ◽  
Highway Capacity Manual ◽  
Flow Adjustment ◽  
Conflict Zone ◽  
Adjustment Factors ◽  
Left And Right ◽  
Saturation Flow ◽  
Green Period

In Chapter 9 of the 1994 update to the 1985 Highway Capacity Manual, the operational and planning analysis of signalized intersections is discussed. The methodology for saturation flow rate estimation does not consider all elements of the interaction between pedestrians and turning vehicles. This study describes this interaction for left and right turns using a conflict-zone-occupancy approach. A conflict zone is a portion of an intersection, typically in the crosswalk, in which pedestrians and vehicles compete for space. Conflict-zone occupancy, defined as the fraction of the effective green period during which pedestrians occupy a conflict zone, provides the basis for a rational adjustment to saturation flow. This study details the results of a multiregional data collection effort that confirms the validity of the conflict-zone-occupancy approach. In addition, this study describes the effect of geometric constraints, as reflected in the number of receiving lanes versus the number of turning lanes, on turning-vehicle saturation flow. After consideration of signalized intersection phasing and turn protection, one can calculate saturation flow adjustment factors reflecting the effect of pedestrians on lane groups containing vehicles turning left ( fLpb) or right ( fRpb).

Model for Minimum Driveway Corner Clearances at Signalized Intersections

1997 ◽  
Vol 1579 (1) ◽  
pp. 53-62
Author(s):  
Gary Long ◽  
Cheng-Tin Gan
Keyword(s):  
Signalized Intersections ◽  
Continuous Variables ◽  
Flow Conditions ◽  
Highway Capacity ◽  
Factors Affecting ◽  
Highway Capacity Manual ◽  
Proposed Model ◽  
Adjustment Factors ◽  
Saturation Flow ◽  
The Ideal

A signalized intersection typically operates under both saturated and undersaturated traffic flow conditions at different times of the day. When an intersection operates under saturated flow conditions, its ability to dissipate traffic becomes a primary matter of concern. On the other hand, safety is often the major concern due to higher vehicular travel speeds associated with undersaturated flow conditions. The minimum corner clearance distances required under the two different flow conditions are not the same. To be effective, minimum corner clearances must be set such that the needs under both types of flow conditions are satisfied. Existing guidelines for minimum corner clearances were reviewed, and none were found to address the capacity issue. A new model designed to meet both capacity and safety needs is proposed. The model produces a refined minimum corner clearance distance by applying a set of adjustment factors to an initial minimum corner clearance, a procedure similar to that of the familiar Highway Capacity Manual for adjusting the ideal saturation flow rate. Unlike existing guidelines, the proposed model is flexible, is much less discrete for continuous variables, and can easily incorporate as many factors affecting corner clearance as needed.

Saturation Flows at Signal-Group-Controlled Traffic Signals

1997 ◽  
Vol 1572 (1) ◽  
pp. 24-32 ◽  
Author(s):  
Jarkko Niittymäki ◽  
Matti Pursula
Keyword(s):  
Field Measurements ◽  
External Factors ◽  
Highway Capacity ◽  
Highway Capacity Manual ◽  
Flow Models ◽  
Control Programs ◽  
Extensive Field ◽  
Lane Width ◽  
Traffic Composition ◽  
Saturation Flow

The main goal of this research was to update the basic saturation flow values of signalized intersections. The secondary goal was to analyze the effects of certain external factors (such as weather, road, and traffic conditions) on saturation flow. The updating is based on extensive field measurements and simulations. Altogether, about 39,000 queues were observed in this study. Field measurements at 30 locations were made according to the method described in the Highway Capacity Manual and simulations were done with the Helsinki University of Technology HUT-SIM simulator, which was calibrated and carefully validated for Finnish road conditions. A summary of calibration parameters is also presented. The new base value for straight-through lanes is 1, 940 vehicles per hour; the previous value was 1, 700 vehicles per hour. In general, the updated saturation flow values of different lane types are 5 to 20 percent larger than the previous base values. The saturation flow models of different lane types are described. The effects of geometric and traffic composition factors, such as percentage of turning vehicles, traffic composition, lane width, and approach grade, were examined and modeled. Effects of weather, road surface, light conditions, and speed level were also analyzed. The drop in saturation flow was about 20 to 30 percent under slippery road and snowy conditions. In rainy conditions, the drop was smaller, about 10 percent. The effect of speed on saturation flow is also described. The most important results of this 2-year project are the saturation flow values for different lane types, knowledge of the effect of external factors (especially during winter), and the large database, which can be used for other purposes. The possibility of using special signal control programs under bad road conditions is discussed. With these kinds of programs, better safety and higher capacity can be achieved.

Modeling Capacity of Through Movement at Signalized Intersection Affected by Short Left-Turn Bay under Different Signal Settings

2021 ◽  
pp. 036119812110064
Author(s):  
Zihang Wei ◽  
Yunlong Zhang ◽  
Xiaoyu Guo ◽  
Xin Zhang
Keyword(s):  
Cycle Length ◽  
Signalized Intersections ◽  
Signalized Intersection ◽  
Essential Factor ◽  
Highway Capacity ◽  
Left Turn ◽  
Highway Capacity Manual ◽  
Proposed Model ◽  
Vehicle Demand ◽  
The One

Through movement capacity is an essential factor used to reflect intersection performance, especially for signalized intersections, where a large proportion of vehicle demand is making through movements. Generally, left-turn spillback is considered a key contributor to affect through movement capacity, and blockage to the left-turn bay is known to decrease left-turn capacity. Previous studies have focused primarily on estimating the through movement capacity under a lagging protected only left-turn (lagging POLT) signal setting, as a left-turn spillback is more likely to happen under such a condition. However, previous studies contained assumptions (e.g., omit spillback), or were dedicated to one specific signal setting. Therefore, in this study, through movement capacity models based on probabilistic modeling of spillback and blockage scenarios are established under four different signal settings (i.e., leading protected only left-turn [leading POLT], lagging left-turn, protected plus permitted left-turn, and permitted plus protected left-turn). Through microscopic simulations, the proposed models are validated, and compared with existing capacity models and the one in the Highway Capacity Manual (HCM). The results of the comparisons demonstrate that the proposed models achieved significant advantages over all the other models and obtained high accuracies in all signal settings. Each proposed model for a given signal setting maintains consistent accuracy across various left-turn bay lengths. The proposed models of this study have the potential to serve as useful tools, for practicing transportation engineers, when determining the appropriate length of a left-turn bay with the consideration of spillback and blockage, and the adequate cycle length with a given bay length.

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