|
The variation of volume with time, i.e. month to month, day to day, hour to
hour and within a hour is also as important as volume calculation.
Volume variations can also be observed from season to season. Volume will be above
average in a pleasant motoring month of summer, but will be more pronounced in
rural than in urban area.
But this is the most consistent of all the variations and affects the traffic
stream characteristics the least.
Weekdays, Saturdays and Sundays will also face difference in pattern.
But comparing day with day, patterns for routes of a similar nature often show
a marked similarity, which is useful in enabling predictions to be made.
The most significant variation is from hour to hour.
The peak hour observed during mornings and evenings of weekdays, which is
usually 8 to 10 per cent of total daily flow or 2 to 3 times the average hourly
volume.
These trips are mainly the work trips, which are relatively stable with time
and more or less constant from day to day.
Since there is considerable variation in the volume of traffic, several types
of measurements of volume are commonly adopted which will average these
variations into a single volume count to be used in many design purposes.
- Average Annual Daily Traffic(AADT) : The average 24-hour traffic
volume at a given location over a full 365-day year, i.e. the total number of
vehicles passing the site in a year divided by 365.
- Average Annual Weekday Traffic(AAWT) : The average 24-hour traffic
volume occurring on weekdays over a full year.
It is computed by dividing the total weekday traffic volume for the year by
260.
- Average Daily Traffic(ADT) : An average 24-hour traffic volume at
a given location for some period of time less than a year.
It may be measured for six months, a season, a month, a week, or as little as
two days.
An ADT is a valid number only for the period over which it was measured.
- Average Weekday Traffic(AWT) : An average 24-hour traffic volume
occurring on weekdays for some period of time less than one year, such as for a
month or a season.
The relationship between AAWT and AWT is analogous to that between AADT and
ADT.
Volume in general is measured using different ways like manual counting,
detector/sensor counting, moving-car observer method, etc.
Mainly the volume study establishes
the importance of a particular route with respect to the other routes,
the distribution of traffic on road, and
the fluctuations in flow.
All which eventually determines the design of a highway and the related
facilities.
Thus, volume is treated as the most important of all the parameters of traffic
stream.
|
