Basic Parameters of Traffic-Stream: Volume
Traffiostream parameters fall into two broad categories: macroscopic parameters characterize the traffic stream as a whole; microscopic parameters characterize the behavior of individual vehicles in the traffic stream with respect to each other.
A traffic stream may he described macroscopically by three parameters:
1 . Volume or rate of flow
Traffic volume is defined as the num[>er of vehicles that pass a point on a highway, or a given lane or direction of a highway, during a specified time interval. The unit for volume is simply "vehicles" , although it is often expressed as vehicles per unit of time.
1 . Daily Volumes and Their Use
A common time interval for volumes is a day. Daily volumes are frequently used as the basis for highway planning and general observations of trends.
Traffic volume projections are often based upon measured daily volumes. Four daily parameters are widely used •
- Average annual daily traffic (AADT) is the average 24-hour traffic volume at a given location
over a full 365-day year梩hat is,the total number of vehicles passing the site in a year divided
by 365.
- Average annual weekday traffic (AAWT) is the average 24-hour traffic volume occurring on
weekdays over a full year. This volume is of considerable interest where weekend traffic is light, so thai
averaging higher weekday volumes over 365 days would mask the impact of weekday traffic. AAWT is
compuled hy dividing the total weekday traffic volume for the year by 260.
- Average daily traffic (ADT) is an average 24-hour traffic volume a! a given location for some
;>eriod of time less than a year.While an AADT is for a full year, an ADT may be measured for six
month, a season, a month, a week, or as little as two days. An ADT is a valid number only for the peri
od over which it was measured.
- Average weekday traffic (AWT) is an average 24-hour traffic volume occurring on weekdays for
some period of time less than one year, such as a month or a season. The relationship between AAWT
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