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Spot speed is the instantaneous speed of a vehicle at a specified location.
Spot speed can be used to design the geometry of road like horizontal and
vertical curves, super elevation etc.
Location and size of signs, design of signals, safe speed, and speed zone
determination, require the spot speed data.
Accident analysis, road maintenance, and congestion are the modern fields of
traffic engineer, which uses spot speed data as the basic input.
Spot speed can be measured using an enoscope, pressure contact tubes or direct
timing procedure or radar speedometer or by time-lapse photographic methods.
It can be determined by speeds extracted from video images by recording the
distance travelling by all vehicles between a particular pair of frames.
Running speed is the average speed maintained over a particular course while
the vehicle is moving and is found by dividing the length of the course by the
time duration the vehicle was in motion.
i.e. this speed doesn't consider the time during which the vehicle is brought
to a stop, or has to wait till it has a clear road ahead.
The running speed will always be more than or equal to the journey speed, as
delays are not considered in calculating the running speed
Journey speed is the effective speed of the vehicle on a journey between two
points and is the distance between the two points divided by the total time
taken for the vehicle to complete the journey including any stopped time.
If the journey speed is less than running speed, it indicates that the journey
follows a stop-go condition with enforced acceleration and deceleration.
The spot speed here may vary from zero to some maximum in excess of the running
speed.
A uniformity between journey and running speeds denotes comfortable travel
conditions.
Time mean speed is defined as the average speed of all the vehicles passing a
point on a highway over some specified time period.
Space mean speed is defined as the average speed of all the vehicles occupying
a given section of a highway over some specified time period.
Both mean speeds will always be different from each other except in the
unlikely event that all vehicles are traveling at the same speed.
Time mean speed is a point measurement while space mean speed is a measure
relating to length of highway or lane, i.e. the mean speed of vehicles over a
period of time at a point in space is time mean speed and the mean speed over a
space at a given instant is the space mean speed.
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