Do you want to read about traffic spot speed study in traffic engineering.?I am here to give you a brief and simple article about spot speeds, their presentation, methods and types.
Spot speed study is done after completing counting of the traffic volume in a place.After the determination of the number of vehicles passing through a section or a small distance.We need to determine the speed of these vehicles passing during this particular stretch of road for the proper design of roads.
You know that usually your vehicle speedometer displays reading in terms of km/hour.But there are other units to indicate the speed of your vehicles.Let us see what are they.
Various units to display the speed of your vehicles.
You are very familiar with spot speed.When you look at your speedometer while driving, the speed indicating will be the spot speed.That is spot speed is the instantaneous speed of a vehicle at a particular section or location of the road.We will learn more about spot speed study in below section.
As its name, the average speed is the average of all spot speeds of various vehicles passing through a given point or section.
Running speed is the average speed maintained by a vehicle over a particular stretch of road.
4.Travel or Journey speed
Journey speed the effective speed of travel of all vehicles along the route between two terminals.
Methods for determination of the spot speed of vehicles
You can determine the spot speed of vehicles by simply looking into the speedometer of your vehicle.Also, you can measure your spot speed of the vehicle from outside like what police always doing.
The instruments that help you to take spot speed from outside is
- Electronic meter method
- Photoelectric method.
- Radar speed meter method.
- Time-lapse method.
Presentation of Spot speed study
The presentation of spot study can be done in two methods, the first one is by frequency distribution curve and the second one is by cumulative speed distribution curve.
1.Frequency Distribution Diagram
The graph above shows the frequency of vehicles on the x-axis and speed of the vehicles on the y-axis.You can see the graph has a peak value at somewhere in the midpoint of the graph.That point is called modal speed.
The modal speed is the point at which greatest number of vehicles travel.The modal speed is the peak value of frequency distribution vs speed curve.
2.Cumulative speed distribution diagram
a.98th percentile speed( Desing speed)
98th percentile speed is taken for the highway pavement design.In 98the percentile speed, 98 percentage of all vehicles are passing below this speed.Only 2% of remaining vehicles will exceeds this speed.
b.85th percentile speed
In 85th percentile speed, 85% of all vehicles are passing below this speed.Only 15% of vehicles are exceeding this speed.When we comparing the above two percentile speed, 85th percentile speed is less than 98th percentile speed as shown in the above graph.This speed is the safe speed of that road.
c.15th percentile speed
In 15 percentile speed, 15% of all vehicles are passing below this speed and the remaining vehicles will be higher than this speed.This should be the minimum maintaining speed of vehicle.
Types of Spot Speed
There are two types of spot speed, Space mean speed and Time mean speed.
1.Space Mean Speed
Space mean speed is the average speed of vehicles in a certain road length at any specified time period.It is very useful for determining vehicle flow characteristics.
2.Time Mean Speed
Time mean speed is the average speed of vehicles passing a point over some specified time period.
I hope you could study this article about Spot Speed Study.If you have any doubt, please ask in below comment section.If you like this post?Don’t forget to share it.