What is a Traffic Intersection?
A traffic intersection is a location where two or more roads join or cross each other, allowing vehicles to change direction. Intersections are the most critical points in any road network — they are where different streams of traffic must share the same space, creating the potential for conflicts and collisions. The purpose of intersection design and control is to reduce these conflicts and improve safety and efficiency.
Three Types of Intersection Conflicts
1. Crossing Conflict (Major)
Crossing conflicts occur when two traffic streams cross each other’s paths at a significant angle — typically near right angles. These are the most dangerous conflicts because the relative speed between the two streams is high, and a collision results in a severe lateral impact. Crossing conflicts include through-through crossings, right-turn crossings, and right-turn-through crossings.
2. Merging Conflict (Minor)
Merging conflicts occur when two separate traffic streams converge into a single stream — moving in approximately the same general direction. Since both streams are moving in similar directions, the relative speed between them is small, making merging conflicts significantly less dangerous than crossing conflicts. They are considered minor conflicts.
3. Diverging Conflict (Minor)
Diverging conflicts occur when a single traffic stream splits into two separate streams. Like merging, the relative speeds are small due to similar direction of movement. Diverging conflicts are generally neglected in conflict count analysis because of their small intersection angles and low risk. They are classified as minor conflicts.
Conflict Count: 2-Lane × 2-Lane Two-Way Intersection
| Conflict Type | Count | Details |
|---|---|---|
| Through crossing | 4 | Straight-through vehicles crossing |
| Right-turn crossing | 4 | Right-turning vehicles crossing path |
| Right-turn-through crossing | 8 | Right turn conflicting with through traffic |
| Merging (left + right) | 8 | 4 left + 4 right turn mergings |
| Diverging | 4 | Neglected (small angle) |
| Pedestrian | 8 | Pedestrians crossing vehicle paths |
| Total vehicular | 24 | After neglecting diverging |
| Total (including pedestrian) | 32 | Complete conflict count |
Conflict Count Table (Various Lane Configurations)
| Road A Lanes | Road B Lanes | Both Two-Way | A=One-Way, B=Two-Way | Both One-Way |
|---|---|---|---|---|
| 2 | 2 | 24 | 11 | 6 |
| 2 | 3 | 24 | 11 | 8 |
| 2 | 4 | 32 | 17 | 10 |
| 3 | 3 | 24 | 13 | 11 |
| 4 | 4 | 44 | 25 | 18 |
Types of Intersection Control
1. Passive Control
Used when traffic volume is low and no explicit control device is needed. Road users are expected to follow traffic rules voluntarily. Road signs and markings like GIVE WAY and STOP signs are used. The driver on the minor road must slow down and give way to traffic on the major road.
2. Semi-Control (Partial Control)
Drivers are gently guided into proper channels to avoid conflict — they are influenced but not forced. Channelisation and traffic rotaries fall under this category. These measures reduce conflict points by physically guiding vehicles through the intersection area.
3. Active Control
Road users are forced to follow the path directed by the traffic control agency. Traffic signals and grade-separated intersections are in this category. Active control completely governs the right-of-way at the intersection.
At-Grade vs Grade-Separated Intersections
- At-grade intersection: All roads join or cross at the same level. Traffic manoeuvres (merging, diverging, crossing, weaving) all occur at one level.
- Grade-separated intersection: Roads cross at different vertical levels (overpass or underpass), eliminating crossing conflicts between the main flows.
- Unchanelised → Chanelised → Rotary → Grade-separated: Order of increasing control effectiveness and decreasing conflict points.