The correct answer is: C. first increases and then decreases after reaching a maximum value at optimum speed.
The maximum capacity of a lane is the maximum number of vehicles that can pass through a point on a road per unit of time. It is affected by a number of factors, including the speed of the traffic stream, the number of lanes, the width of the lanes, the presence of intersections, and the type of vehicles.
The relationship between the speed of the traffic stream and the maximum capacity of a lane is not linear. At low speeds, the maximum capacity is low because vehicles are not traveling close together and there is a lot of space between them. As the speed of the traffic stream increases, the maximum capacity increases because vehicles are able to travel closer together and there is less space between them. However, at high speeds, the maximum capacity decreases because vehicles are traveling so close together that they start to interfere with each other. This is known as the “traffic wave” effect.
The optimum speed for a lane is the speed at which the maximum capacity is reached. This speed is different for different roads and traffic conditions. It is important to maintain the optimum speed on a road in order to maximize the flow of traffic.
Option A is incorrect because the maximum capacity of a lane decreases at high speeds.
Option B is incorrect because the maximum capacity of a lane increases at low speeds.
Option D is incorrect because the maximum capacity of a lane does not first decrease and then increase.