Effects of Inadequate Driveway Corner Clearances on Traffic Operations, Safety, and Capacity

1997 ◽  
Vol 1579 (1) ◽  
pp. 35-42 ◽  
Author(s):  
Cheng-Tin Gan ◽  
Gary Long
Keyword(s):  
Conflict Analysis ◽  
Traffic Operations ◽  
Inventory Data ◽  
Flow Rates ◽  
Left Turn ◽  
Turn Signal ◽  
Arterial Streets ◽  
Operational Safety ◽  
Traffic Conflict ◽  
Saturation Flow

Inadequate driveway corner clearances can result in traffic operational, safety, and capacity problems. These problems can be caused by blocked driveway ingress and egress movements, incomplete turning maneuvers, conflicting intersection turning movements, confusing right-turn signal indications, insufficient weaving and merging section lengths, and various other conflicts. The effects of driveway corner clearances on safety cannot be examined easily through safety records given the current condition of the available crash and system inventory data. This provides incentives for applying theoretical traffic conflict analysis. A simple conflict analysis showed an increase in merging and crossing conflict points for driveways situated near intersections. Inadequate corner clearance can have a capacity-reducing effect. Driveway capacity may be reduced by ( a) vehicles on the arterial blocking driveway egress movements and ( b) a decreased opportunity for left-turn egress movement on arterial streets designed for platoon progression. Intersection capacity can also be reduced by a decrease in saturation flow rates due to driveway ingress and egress movements.

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.

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.

scholarly journals Estimation of saturation flow rates on dual left-turn lanes

Tehnika ◽  
2018 ◽  
Vol 73 (2) ◽  
pp. 254-261 ◽  
Author(s):  
Anica Kocić ◽  
Nikola Čelar ◽  
Jelena Kajalić ◽  
Stamenka Stanković
Keyword(s):  
Flow Rates ◽  
Left Turn ◽  
Saturation Flow

Impact of Turning Lane Storage Length and Turning Proportions on Throughput at Oversaturated Signalized Intersections

2021 ◽  
pp. 036119812110171
Author(s):  
A. M. Tahsin Emtenan ◽  
Christopher M. Day
Keyword(s):  
Flow Rate ◽  
Cycle Length ◽  
Signal Timing ◽  
Real World Data ◽  
Left Turn ◽  
Common Response ◽  
Cycle Lengths ◽  
Saturation Flow Rate ◽  
Saturation Flow ◽  
Timing Strategies

During oversaturated conditions, common objectives of signal timing are to maximize vehicle throughput and manage queues. A common response to increases in vehicle volumes is to increase the cycle length. Because the clearance intervals are displayed less frequently with longer cycle lengths and fewer cycles, more of the total time is used for green indications, which implies that the signal timing is more efficient. However, previous studies have shown that throughput reaches a peak at a moderate cycle length and extending the cycle length beyond this actually decreases the total throughput. Part of the reason for this is that spillback caused by the turning traffic may cause starvation of the through lanes resulting in a reduction of the saturation flow rate within each lane. Gaps created by the turning traffic after a lane change may also reduce the saturation flow rate. There is a relationship between the proportions of turning traffic, the storage length of turning lanes, and the total throughput that can be achieved on an approach for a given cycle length and green time. This study seeks to explore this relationship to yield better signal timing strategies for oversaturated operations. A microsimulation model of an oversaturated left-turn movement with varying storage lengths and turning proportions is used to determine these relationships and establish a mathematical model of throughput as a function of the duration of green, storage length, and turning proportion. The model outcomes are compared against real-world data.

scholarly journals Safety Impacts of Converting Two-Way Left-Turn Lanes to Raised Medians and Associated Design Concerns

2016 ◽  
Author(s):  
Priyanka Alluri ◽  
Albert Gan ◽  
Kirolos Haleem
Keyword(s):  
Data Availability ◽  
Left Turn ◽  
Arterial Streets ◽  
Crash Data ◽  
Potential Safety ◽  
Before And After ◽  
Show Evidence ◽  
Crash Types ◽  
Associated Design ◽  
Urban Arterial

Raised medians and two-way left-turn lanes (TWLTLs) are the two most common types of median treatments on arterial streets. This paper aims to conduct a detailed study on the safety impacts of conversion from TWLTLs to raised medians on state roads in Florida. In addition, the study also investigated several potential safety concerns related to raised medians on state roads, including crashes at median openings, vehicles directly hitting the median curb, and median crossover crashes. Based on data availability, 17.51 miles of urban arterial sections in Florida that were converted from TWLTLs to raised medians were analyzed. Police reports of all the crashes before and after median conversion were reviewed to correct miscoded crash types and obtain additional detailed crash information. Overall, a 28.5% reduction in total crash rate was observed after the 10 study locations were converted from TWLTLs to raised medians. The reductions in the proportions of left-turn and right-turn crashes were statistically significant, while the changes in the proportions of other crash types were not statistically significant. Furthermore, the crash data did not show evidence that raised medians are an additional hazard compared with TWLTLs.

Trajectory-Based Measurement of Signalized Intersection Capacity

2019 ◽  
Vol 2673 (10) ◽  
pp. 370-380 ◽  
Author(s):  
Walid Fourati ◽  
Bernhard Friedrich
Keyword(s):  
Cycle Time ◽  
Degree Of Saturation ◽  
Limiting Factor ◽  
Signal Timing ◽  
Flow Rates ◽  
Practical Applications ◽  
Road Intersections ◽  
Good Signal ◽  
Saturation Flow ◽  
Over Time

Capacities of road intersections are a limiting factor and crucial for the performance of road networks. Therefore, for purposes of intersection design and of optimal signal timing, numerous methodologies have been proposed to either estimate or directly measure the capacity of single movements at road intersections. However, both model-based estimation and direct measurement suffer from the large effort that is needed to gather the relevant data. Even worse, once the data are collected they only represent a snapshot of the capacity over time. This paper proposes an alternative approach to estimate capacity of signalized road intersections over time using only automatically generated trajectories of probe vehicles. The obtained capacity can be used to evaluate the effective degree of saturation using real demand, or to assess hypothetic different conditions in demand or signaling. The cyclic operation of signalized intersections allows for the accumulation of trajectories, and thus in practical applications for the compensation of potentially low penetration rates. Within a sequential process the intersection’s cycle time and the approach green time and saturation flow rates are determined. The determination of the cycle time and the green times is based on an existing approach. The derivation of the saturation flow rates relies on its direct dependency to the saturation time headway and uses two parameters to be calibrated. Testing with a commercial dataset on an intersection in Munich produced a good signal timing estimation and saturation flow values that are comparable to a calculation based on the German guideline.

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