Unsignalized Intersections
Unsignalized intersections are those where at least one of the movements is controlled by a STOP or a YIELD sign. Operations of such facilities require the drivers on the controlled movements (usually referred to as minor movements) to judge the size of t
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Unsignalized Intersections
Unsignalized intersections are those where at least one of the movements is controlled by a STOP or a YIELD sign. Operations of such facilities require the drivers on the controlled movements (usually referred to as minor movements) to judge the size of the gaps along the major (or uncontrolled) street and select a suitable one to cross or to merge into. Unsignalized intersections include two-way stop-controlled (TWSC) and all-way stop-controlled (AWSC) intersections, as well as roundabouts. Figure 10.1 provides sketches of these three types of facilities. At the TWSC intersection shown in Fig. 10.1a, minor movements include left, through, and right turns from the two minor approaches (NB and SB), as well as left turns from the two major approaches (EB and WB). High demand along the major street limits the opportunities for minor street vehicles to enter or cross. The leftturn movements from the major street have priority over the minor street movements, while the through and right movements from the minor streets have priority over the respective left-turn movements. These priority rules, combined with the intersection geometry and the relative demands of each movement, affect the capacity of each minor movement. At AWSC intersections (Fig. 10.1b), arriving vehicles are required to proceed in a priority sequence (first come, first served), and thus, operations are slightly different than those at TWSC. Drivers do not need to judge the size of gaps in order to proceed, but they do need to observe their priority position relative to other vehicles at the intersection when they arrive at the stop bar. The capacity of each approach is a function of the demand in the other approaches; the higher the demand in the other approaches, the lower the capacity of the subject approach. Roundabouts are traffic circles where the circulating traffic has priority and the entering traffic has to yield to the circulating traffic. Thus, at roundabouts, drivers have to judge the gaps within the circulating stream. Roundabouts are designed to reduce the speed of approaching vehicles without requiring them to stop. The angle of the approach to the circulating traffic stream allows vehicles to enter the roundabout at a higher speed. Therefore, all things being equal, the capacity of a roundabout approach would be higher than the equivalent right-turn movement L. Elefteriadou, An Introduction to Traffic Flow Theory, Springer Optimization and Its Applications 84, DOI 10.1007/978-1-4614-8435-6_10, © Springer Science+Business Media New York 2014
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Fig. 10.1 Three types of unsignalized intersections
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Unsignalized Intersections
Principles of Gap Acceptance
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Fig. 10.2 Trajectory of vehicle approaching a stop sign (TWSC) vs. a yield sign (roundabout)
from a stop-controlled approach. Similarly, the delay to the roundabout approach vehicles would be lower than that of a stop-controlled intersection. Figure 10.2 illustrates the trajectory of a vehicle approaching a stop sign vs. that of a vehicle ap
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