Correct Answer - Option 3 : running speed
Concepts:
The different types of speed considered in Traffic flow analysis are:
1. Spot Speed: This is the instantaneous speed of a vehicle at a specified location. Spot speeds are useful to study points of congestion, for locating traffic signals, or for enforcing speed limits.
2. Running Speed: This is the average speed maintained by a vehicle over a given stretch of highway while the vehicle is actually in motion; the running speed is determined by dividing the length of the stretch by the time for which the vehicle is in motion (excludes that part of the journey time for which the vehicle suffers delay, for example, at controlled intersections.) They are useful to assess the traffic capacity of highways.
3. Overall Speed or Journey Speed: This is the effective speed with which a vehicle covers a particular route between two terminals; this is, the average speed obtained by dividing the total distance covered by the total time taken including all delays, but excluding voluntary stoppages, if any.
It cannot be more than running speed as such total journey time is always greater than or equal to running time. They are useful to assess the adequacy of an existing road network as also the efficiency of the improvement measures and for cost-benefit studies of a project.
The journey speed is less than running speed indicates that there is some time lapsed/delay at intersection which causes enforced acceleration and deceleration
If Journey Speed is equal to running speed, it means that there is no delay at intersections.
4. Operating Speed: It is the sustained running speed at which a vehicle can travel under the existing traffic and environmental conditions.
5. Average Speed: There are two different types of average speed obtained from spot speeds of vehicles-
Time-mean speed and space-mean speed.
Time-mean speed is defined as the average of the speed measurements at one point in space of all the vehicles passing over a period of time. It is the arithmetic mean of all spot speeds.
Space-mean speed is defined as the average of speed measurements at a particular instant of time of all vehicles over a particular stretch of the highway. It is harmonic mean of all spot speeds.
