1. INTRODUCTION
An intersection is the general area where two or more highways join or cross, including the roadway and roadside facilities for traffic movements within the area.
Intersections are an important part of a highway facility because their design affect greatly the efficiency, safety, cost of operation, and capacity of the facility.
There are three types of intersections: at-grade intersections, grade separations without ramps, and interchanges.

2. DESIGN CONSIDERATIONS AND OBJECTIVES
The main objective of intersection is to facilitate the convenience, ease, and comfort of people traversing the intersection while enhancing the efficient movement of motor vehicles, buses, trucks, bicycles, and pedestrians.
Five basic elements are human factors, traffic considerations, physical elements, economic elements, and functional intersection area.
An intersection has its functional and physical area. See Exhibits 9-1 and 9-2. The functional area extends both upstream and downstream from the physical intersection area and includes any auxiliary lanes and their associated channelization. It has three basic distances: perception-reaction distance, maneuver distance, and queue-storage distance.
Driveways cannot be located within the functional area of an intersection.

3. INTERSECTION TYPES
Basic intersections are three-leg (or T), four leg, and multi-leg intersections.
Type = f( number of intersecting legs, topography, character of the intersecting highways, traffic volumes, patterns, speeds, and type of operation)
Once an intersection type is determined, a geometric plan should be created.
Traffic control related to an intersection can be cautionary or non-stop control, stop control for minor approaches, four-way stop control, and both fixed-time and traffic-actuated signal control.

4. INTERSECTION TYPES Three-Leg Intersections See Exhibit 9-3 to 9-8
Exhibit 9-5A is the most common intersection that is suitable for junctions of minor or local roads, junctions of minor roads with more important highways with angle greater than 60°. Check the conflicting points in the intersection.
When the speeds and turning movements are high, Exhibit 9-5B and Exhibit 9-6.
The use of auxiliary lanes, such as left- and right-turn lanes, increases capacity and creates better operational conditions for turning vehicles.

5. INTERSECTION TYPES Three-Leg Intersections See Exhibit 9-3 to 9-8
Exhibit 9-5A is the most common intersection that is suitable for junctions of minor or local roads, junctions of minor roads with more important highways with angle greater than 60°. Check the conflicting points in the intersection.
When the speeds and turning movements are high, Exhibit 9-5B and Exhibit 9-6.
The use of auxiliary lanes, such as left- and right-turn lanes, increases capacity and creates better operational conditions for turning vehicles.

6. INTERSECTION TYPES Four-Leg Intersections
See Exhibit 9-9 to The overall design principles, island arrangements, use of auxiliary lanes, and many other design aspects are same as those for three-leg intersections.
Exhibit 9-9A is the simplest form of an unchannelized four-leg intersection that is suitable for junctions of minor or local roads, junctions of minor roads with more important highways with angle greater than 60°. Check the conflicting points in the intersection.
Exhibit 9-9B shows the use of flare to increase capacity for through and turning movements at the intersection. Flare can be done by adding parallel auxiliary lanes or adding pavement tapers.
Exhibit 9-9C shows a flared intersection with a a marked pavement area to divide traffic approaching the intersection

7. INTERSECTION TYPES Four-Leg Intersections
The usual configurations of four-leg intersections with simple channelization are shown in Exhibits 9-10 and 9-11.
Exhibit 9-10A right-turn roadways are provided
Exhibit 9-10B an oblique-angle intersection with a skew angle of 45 degrees or more with separate turning roadways for two-way traffic in the acute-angle quadrants. Undesirable
Exhibit 9-11A right-turning roadways in all four quadrants
for high turning volumes
Exhibit 9-11B shows division islands on the cross roads.
Exhibit 9-11C suitable for two-lane highways near capacity.

8. INTERSECTION TYPES Four-Leg Intersections
The usual configurations of four-leg intersections with simple channelization are shown in Exhibits 9-10 and 9-11.
Exhibit 9-12A a high type intersection on a divided highway
Exhibit 9-12B right-turning roadways with speed-change lanes and median lanes for left turns
Exhibit 9-13A A configuration with dual left-tuning lanes for one of the left-tuning movements.
Exhibit 9-13B Suitable for an intersection with usually heavy through volumes and a high left-turning volume in one quadrant. It creates two additional intersections.

9. INTERSECTION TYPES Multi-Leg Intersections
Intersections with five or more legs. Should be avoided as much as possible. See Exhibits 9-14 for the methods of converting
a five-leg intersection into two intersections (T and four-leg intersections)
a six-leg intersection into two intersections (two four-leg intersections)

10. INTERSECTION TYPES Modern Roundabouts and Traffic Circles
An emergence of interest in modern roundabouts in some parts of the United States is experienced. Only about 50 modern roundabouts.
Modern roundabouts are different from nonconforming traffic circles or rotaries in the following areas:
Yield at Entry: yield to left rule. It requires that vehicles on the circulatory roadway of the roundabout have the right-of way and all entering vehicles on the approaches have to wait for a gap in the circulating flow.
Deflection of Entering Traffic: Entrance roadways that intersect the roundabout along a tangent to the circulatory roadway are not permitted.

11. INTERSECTION TYPES Modern Roundabouts and Traffic Circles
Modern roundabouts has three sizes:
Mini-roundabouts 15 m inscribed circle diameter
compact roundabouts m
large roundabouts up to 150 m
See Exhibit 9-15 for elements of the one-lane modern roundabout.
Design of a roundabout involves choosing the best operational and capacity performance at slow speed while retaining the best safety enhancements.
Entry width is the largest determinant of a roundabout’s capacity.
Entry Width = f( number of entering lanes, total width of entry)

12. INTERSECTION TYPES Modern Roundabouts and Traffic Circles
To maximum a roundabout’s safe and efficient operations, entry widths should be kept to a minimum, while capacity needs and performance objectives should be considered in determining the width and number of lanes for each entry.
Pedestrian crossing locations at roundabouts should achieve a balance among pedestrians convenience and safety, and roundabout operations. Crossing locations and crossing distance are two important factors in design of roundabouts with pedestrians involved.
The location of pedestrian crosswalks at the yield line is discouraged. It is preferred to be an even increase of vehicle length at the distance from the yield line.

13. INTERSECTION TYPES Modern Roundabouts and Traffic Circles
The designers should provide bicyclists the choice of proceeding through the roundabout as either a vehicle or pedestrian. Bicycle lanes should be terminated in advance of the roundabout to encourage bicyclists to mix with vehicle traffic.
To accommodate bicyclists traveling as pedestrians, a bicycle path or a shared bike/pedestrian path, physically separated from the circulatory roadway, should be provided.