Aspects Regarding Priority Settings
in Unsignalized Intersections
and the Influence on the Level of Service
Dumitru Ilie, Matei Lucian, Vînatoru Matei, Racilă Laurențiu
and Oprica Theodor
Abstract The authors study in this paper mathematical models that rely on input
data type like: intersection type, access stages and duration, approach grade,
number of branches, number of lanes, types of tapes, flared approaches, etc. After
establishing a mathematical algorithm based on the detailed characteristics of different types of priority intersections we determine the potential capacity those
intersections types as basis for subsequent development of the area as well as
testing factor for the optimum conditions of road traffic. The results allow the
development of models and simulations in software platforms (ex. AIMSUN,
VISSUM) that can be quantified in optimization solutions.
Keywords Level of service Uncontrolled intersection
Queue length Four-leg intersection Traffic priority
Movement capacity D. Ilie (&) M. Lucian V. Matei R. Laurențiu O. Theodor
Faculty of Mechanics, University of Craiova, Craiova, Romania
e-mail: [email protected]
M. Lucian
e-mail: [email protected]
V. Matei
e-mail: [email protected]
R. Laurențiu
e-mail: [email protected]
O. Theodor
e-mail: [email protected]
© Springer International Publishing Switzerland 2016
C. Andreescu and A. Clenci (eds.), Proceedings of the European Automotive
Congress EAEC-ESFA 2015, DOI 10.1007/978-3-319-27276-4_63
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Introduction
Intersections and interchanges are major points of conflict for road users and are the
frequent site of injuries and fatalities. Intersections also have a significant impact on
the mobility of pedestrians and bicyclists (Andrews et al. 1998).
The speed and ease with which they can move through an intersection is affected
by the signal timing scheme, the number and configuration of lanes, width of the
traveled way, presence of a median or refuge islands, traffic calming configurations,
roadsides, landscaping features, traffic volumes, and other factors.
Transport problem today comes under new forms due to natural desire that need
to meet the needs of safe travel, speed, comfort, economy and environmental
protection (Andrews et al. 1998; Box et al. 1994).
Meeting these needs today we need to address a few areas like:
• Infrastructure, designed in the past and no longer correspond to current standards, and to the future needs;
• Lack of funds due, at present, to difficult economic situation;
• The need to maintain old constructions makes widening of some streets
impossible and arranged the streets along major traffic flows (Robertson and
Bretherton 1991).
Priority of Streams in Intersections
An intersection is a road junction where two or more roads either meet or cross at
grade. This intersection includes the areas needed for all modes of travel: pedestrian, bicycle, motor vehicle, and transit. Thus, the intersection includes not only the
pavement area, but typically the adjacent sidewalks and pedestrian curb cut ramps.
All the road junctions designated for the vehicles to turn to different directions to
reach their desired destinations. Traffic intersections are complex locations in any
cities. This is because vehicles moving in different direction want to occupy same
space at the same time (Stewart and Aerde 1998).
Basically, there are four types of intersections, determined by the number of road
segments and priority usage.
• Priority Intersection: Occur where one of the intersecting roads is given definite
priority over the other;
• Space sharing intersection: Are intended to permit fully equally priority and to
permit continuous movement for all intersecting vehicle flows;
• Time Sharing Intersection: Are those at which alternative flows are given the
right of way at different point in time (Transportation Research Board 2010);
• Uncontrolled intersection: are the most common type of intersection usually
occurs where the intersecting roads are relatively equal importance and found in
areas where there is not much traffic shown.
Aspects Regarding Priority Settings …
Fig. 1 Four-leg intersection priority type 1, 2, 3, 4, 5 and 6
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The paper study the influence of potential capacity of four-leg priority controlled
intersection on the level of service of the intersection. The methodology provides,
beside the current studied TWSC Intersections and AWSC Intersections, a method
to calculate the potential capacity of the road for all types of priority’s in intersection given by the Romanian legislation. So for a four-leg intersection we can
identify 6 types of priorities based on the conflict traffic movements in the intersections (Fig. 1).
Potential Capacity Calculation
Priority matrix constants. In the mathematical model, the priority of right-of-way
given to each traffic stream must be identified. Some streams have absolute priority,
whereas others have to give way or yield to higher-order streams so it has been
identified for a four-leg intersection 4 movement ranks:
• Movements of Rank 1 includes the priority movement of the major streets.
• Movements of Rank 2 (subordinate to 1) include the traffic movements that will
give way or stop to and only to Rank 1 movements (can be movements from the
major streets and movements from the minor streets).
• Movements of Rank 3 (subordinate to 1 and 2) include the traffic only from the
minor street and the movements will give way or stop to and only to Rank 1 and
Rank 2 movements.
• Movements of Rank 4 (subordinate to all others) include the traffic only from
the minor street and the movements will give way or stop to and only to Rank 1,
Rank 2 and Rank 3 movements. Rank 4 movements only occur at four-leg
intersections.
Starting from this we needed to isolate the type of movement realized in all types
of intersection and introduce is into a constant priority matrix based on the
movement rank and geometrical characteristics of the intersection (Robertson and
Bretherton 1991; Stewart and Aerde 1998; Transportation Research Board 2010).
The priority constants matrix can be seen in the Figs. 2 and 3.
Geometrical characteristics of the intersection. Road conditions include
geometric and other elements on which the traffic rely on so it will be without
congestions (Transportation Research Board 2010). In some cases, these influence
the capacity of a road; in others, they can affect a performance measure such as
speed, but not the capacity or maximum flow rate of the facility.
Geometric factors include the following (Transportation Research Board 2010):
•
•
•
•
•
Number of lanes from the major and minor streets;
The type of facility and its development environment;
Lane widths;
Shoulder widths and lateral clearances;
Design speed;
Aspects Regarding Priority Settings …
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Fig. 2 Priority constant matrix for every type of four-leg intersection movement
Fig. 3 Movement rank matrix
•
•
•
•
Flared approaches;
Horizontal and vertical alignments;
Traffic from nearby intersections does not back up into the subject intersection;
A separate lane is provided for the exclusive use of each minor-street
movement;
• An upstream signal does not affect the arrival pattern of the major-street traffic;
• No other movements of Rank 2, 3, or 4 impede the subject movement;
Taking into account that the potential capacity of the intersection is subject to all
the geometrical characteristics of the intersection and to all the changes that are
made to it the formula for the geometrical factors takes into account all of this and
can be seen in the Fig. 4.
Conflicting volume calculation. Each movement at a four-leg priority intersection faces a different set of conflicts that are directly related to the nature of the
movement (Brilon 2011).
The conditions that are integrated as factors into the mathematical model are
calculated based on the geometrical characteristics of the intersection and are based
on the following criteria:
• The right-turning traffic from the major street is separated by a triangular island.
• The number of lanes one lane on the major street for every stream.
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Fig. 4 Geometrical characteristics of the intersection
• The right-turn lane on the major street is separated from the rest of the
movements.
• The minor approach is flared.
• The access from the minor movements is done in two separate stages.
Again in the mathematical model the conflict traffic volumes are calculated
based on the real traffic volumes and the geometrical characteristics of the intersection that is added into the formula based on the priority constant matrix, see
Figs. 5 and 6.
Potential capacity. Capacity is defined as the maximum number of vehicles,
passengers, or the like, per unit time, which can be accommodated under given
conditions with a reasonable expectation of occurrence. Potential capacity describes
Fig. 5 Traffic volumes based
on the geometrical factor of
the intersection
Aspects Regarding Priority Settings …
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Fig. 6 Conflicting volume
the capacity of a minor stream under ideal conditions assuming that it is unimpeded
by other movements and has exclusive use of a separate lane (Mueller and Claudio
2014).
Once the conflicting volume, critical gap and follow up time are known for a
given movement its potential capacity can be estimated using gap acceptance
models. The concept of potential capacity assumes that all available gaps are used
by the subject movement i.e.; there are no higher priority vehicular or pedestrian
movements and waiting to use some of the gaps it also assumes that each movement
operates out of an exclusive lane. The potential capacity of is calculated using the
formula shown in the Fig. 7.
Fig. 7 Potential capacity
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Conclusion
The potential capacity calculation for every type of priority in a four-leg intersection is important in the evaluation of traffic based on the following:
• We can juggle with the geometrical characteristics of the intersection so we can
maintain a lower delay for the intersection or approach priority desired and this
can be seen in the Level of Service calculation;
• The priority effect for an independent intersection can be evaluated based on the
potential capacity and LOS calculation. Thus the correct measures for decongesting the intersection can be taken;
• We can analyze the traffic flow and the delay for multiple intersection in a zone
based on different scenarios for upstream intersection priority.
Acknowledgements This research article was supported by: (1) Grant no. P09003/1138/
31.03.2014—“Virtual design of mechatronic and robotic applications specific to the automotive
industry and transportation-PV-AMR”—Competitiveness Pole “Automotive Sud-Vest Oltenia”;
(2) Grant no. 12P09002/08.05.2013—“Research to implement an advanced maintenance system in
automotive industry in order to increase the degree of competitiveness”, Competitiveness Pole
“Automotive Sud-Vest Oltenia”.
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