Module 6 : Traffic Intersection Control
Lecture 30 : Uncontrolled Intersection
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Conflicting volume

The traffic flow process at un-controlled intersection is complicated since there are many distinct vehicular movements to be accounted for. Most of this movements conflict with opposing vehicular volumes. These conflicts result in decreasing capacity, increasing delay, and increasing potentials for traffic accidents. Consider a typical four-legged intersection as shown in Fig. 1 The numbers of conflicts for competing through movements are 4, while competing right turn and through movements are 8. The conflicts between right turn traffics are 4, and between left turn and merging traffic are 4. The conflicts created by pedestrians will be 8 taking into account all the four approaches. Diverging traffic also produces about 4 conflicts. Therefore, a typical four legged intersection has about 32 different types of conflicts.
Figure 1: Conflicts at four legged intersection
\begin{figure} \centerline{\epsfig{file=qfUnCtrlConflictsAtFourLegged.eps,width=8cm}} \end{figure}
Conflicts at an intersection are different for different types of intersection. The essence of the intersection control is to resolve these conflicts at the intersection for the safe and efficient movement of both vehicular traffic and pedestrians. The movements for determining conflict in four legged intersection are:
  1. Major street left turns seek gaps through the opposing through movement, the opposing right turn movement and pedestrians crossing the far side of the minor street.
  2. Minor street right turns seek to merge in to the right most lane of the major street, which contains through and right turning vehicles. Each right turn from the minor street must also cross the two pedestrians path shown.
  3. Through movements from the minor street must cross all major street vehicular and pedestrians flows.
  4. Minor street left turns must deal not only with all major street traffic flow but with two pedestrians flows and the opposing minor street through and right turn movements.
Through this movements the conflict volume ($ V_{cx}$) for the given movement $ x$ is can be computed. As an example the formula of conflict volume for movement 7 for three legged intersection shown in Fig. 2 computed as:

$\displaystyle V_{c7} = 2V_{c4}+V_{c5}+V_{c2}+0.5V_3+V_{13}+V_{15}$ (1)

Figure 2: Three legged intersection conflicts volume determination for movement 7
\begin{figure} \centerline{\epsfig{file=qfUnCtrlConflictsAtThreeLegged.eps,width=8cm}} \end{figure}