The speed-time curve for the urban service has no Free-running period.

Urban service refers to transportation systems that operate within densely populated urban areas. These systems typically include buses, trams, and trains that provide transportation within cities. The speed-time curve represents the variation of speed with time during the operation of these vehicles.

Explanation:

A) Coasting Period: The coasting period refers to the phase when the vehicle is not accelerating or decelerating and maintains a constant speed. In other words, the vehicle is moving without any external force acting on it. This phase occurs when the vehicle is moving on a level surface or when the driver releases the accelerator pedal. During the coasting period, the speed remains constant. However, in urban service, coasting periods can occur when the vehicle is moving downhill or when there is no traffic.

C) Braking Period: The braking period occurs when the driver applies the brakes to slow down or stop the vehicle. During this period, the speed of the vehicle decreases, and the rate of deceleration depends on the braking force applied. In urban service, braking periods are common at traffic signals, intersections, or when the vehicle needs to slow down to pick up or drop off passengers.

D) Acceleration Period: The acceleration period occurs when the driver increases the speed of the vehicle. This phase can happen when the vehicle starts from rest, overtakes another vehicle, or accelerates after a stop. During this period, the speed of the vehicle increases, and the rate of acceleration depends on the applied throttle or power.

B) Free-Running Period: The free-running period refers to the phase when the vehicle is moving at a constant speed without any acceleration or deceleration. In other words, the vehicle maintains a steady speed without any external forces acting on it. This phase can occur when the vehicle is moving on a straight, level road with no traffic or obstacles. However, in urban service, there are typically frequent stops and starts due to traffic, pedestrians, and other factors, making it unlikely to have a free-running period.

Therefore, the correct answer is option B, which states that the speed-time curve for the urban service has no free-running period.