Test: Design of Traffic Intersections - Civil Engineering (CE) MCQ

The intersection at grade include un channelized, channelized and rotary intersections, the different level intersections are used for over pass and under pass.

Intersection is an area shared by two or more roads. Its main function is to guide vehicles to their respective directions. The essence of the intersection control is to resolve crossing conflicts at the intersection for the safe and efficient movement of both vehicular traffic and pedestrians with an objective of minimum

1. Time sharing: Time shared by each vehicle during crossing the intersection. It includes the stopping time, starting time and time required to cross the intersection. Here we have only control over the delay time as other aspects depend upon the vehicular characteristics and driver characteristics.
2. Space sharing: It is the space occupied by the vehicle. Generally it relates with the density of vehicle.

So, in a well-designed signalized intersection total delay is minimized to avoid the conflicts with proper time sharing.

An intersection that is provided for different levels of road is called grade separated intersection, thus eliminating the crossing manoeuvre.

For Choice W: 

For Choice X: 

For Choice Y:

For Choice Z:

From the above diagram it is clear that Phase-2 and Phase- 3 of choice Z is not recommended as conflict point will form while traffic flows in these phases.

The relative velocity is the difference of the velocities moving in same direction and sum of the velocities of vehicle moving in opposite direction.

Intersection:
An intersection is an at-grade junction where two or more roads or streets meet or cross. Intersections may be classified by a number of road segments, traffic controls, or lane design. In general, there are two types of intersections including signalized and unsignaled intersections.
Basic requirements of the intersection at grade

• Good lighting at night is desirable
• A sudden change of path should be avoided
• Geometric features should be adequately provided
• Rotaries are self-governing and do not need practically any control by police or traffic signals.

Advantages

• Traffic flow is regulated to only one direction of movement, thus eliminating severe conflicts between crossing movements.
•  All the vehicles entering the rotary are gently forced to reduce the speed and continue to move at a slower speed. Thus, none of the vehicles need to be stopped, unlike in a signalized intersection. 
• Because of the lower speed of negotiation and elimination of severe conflicts, accidents, and their severity are much less in rotaries.
• They are ideally suited for moderate traffic, especially with irregular geometry, or intersections with more than three or four approaches.

Disadvantages

• All the vehicles are forced to slow down and negotiate the intersection. Therefore, the cumulative delay will be much higher than a channelized intersection.
• Even when there is a relatively low traffic, the vehicles are forced to reduce their speed.
• Rotaries require a large area of relatively flat land making them costly in urban areas.
• The vehicles do not usually stop at a rotary. They accelerate and exit the rotary at relatively high speed. Therefore, they are not suitable when there are high pedestrian movements

If the angle of merging is small, then the relative velocity will be low and impact will be low.

If an additional pavement is provided for lane change, then that intersection is called as flared intersection, it is provided in very crowded areas.