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 Movement capacity Queue length Four-leg intersection Traffic priority D. Ilie (&) M. Lucian V. Matei R. Laurențiu O. Theodor Faculty of Mechanics, University of Craiova, Craiova, Romania e-mail: dumitru_ilie@yahoo.com M. Lucian e-mail: mateiclucian@gmail.com V. Matei e-mail: mvinatoru2000@yahoo.com R. Laurențiu e-mail: racila_laurentiu@yahoo.com O. Theodor e-mail: oprica_theodor@yahoo.com 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_63 687
688 D. Ilie et al. 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 689 Fig. 1 Four-leg intersection priority type 1, 2, 3, 4, 5 and 6
690 D. Ilie et al. 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 691 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.
692 D. Ilie et al. 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 693 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
694 D. Ilie et al. 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. References Andrews CM, Elahi SM, Clark JE (1998) Traffic-Control System in Transportation Research Record, pp 150 155 Box GP, Jenkins G, Reisel G (1994) Time series analysis: forecasting and control. Prentice Hall, Englewood Cliffs, NJ Brilon W (2011) Delay at unsignalized intersections. D 44 780 Bochum, Germany Robertson DI, Bretherton RD (1991) Optimizing networks of traffic signals in real time the SCOOT method. IEEE Trans Veh Technol 40(1) Stewart JA, Aerde MV (1998) An assessment of adaptive co-ordination of traffic signal offsets within integration. Traffic Eng Control 39:435 443 Transportation Research Board (2010) American Association of State Highway and Transportation Officials (AASHTO) and Federal Highway Administration. Highway Capacity Manual 2010 Mueller J, Claudio D (2014) Simulating unsignalized intersection right-of-way. Department of Mechanical and Industrial Engineering, Montana State University Bozeman, MT pp 59717 3800