Topic2ConceptandTermsNotes2007 - CEE 4600 Fall 2007...

CEE 4600 Concepts and Traffic Engineering Definitions
Fall 2007 Page 1 of 8
Average Annual Daily Traffic -- the total yearly volume divided by the number of days in the
year, commonly abbreviated as AADT. [Note: This value is a total volume for
both directions of travel.]
Average Daily Traffic -- the average 24-hour traffic volume at a given location for some period
of time less than a year, commonly abbreviated as ADT. While an AADT is
for a full year, an ADT may be measured for six months, a season, a month, or
as little as a few days. [Note: This value is a total volume for both directions
of travel.]
Use of AADT and ADT:
Traffic volume information is extremely important in traffic planning, design, operation, and
research. Types of volume information vary according to the application of the data.
Annual total traffic volumes are used for:
1. Measuring and establishing trends in traffic volume.
2. Determining annual travel in vehicle miles as economic justification for proposed
expenditures.
3. Computing accident rates per 100 million vehicle-miles.
4. Estimating highway user revenues.
AADT or ADT volumes are used for:
1. Highway planning activities, such as developing freeway systems and major or
arterial street systems, selecting through streets, and selecting the best route for a
new facility or improvement.
2. Highway programming to determine the need for and priority of street
improvements.
3. Measuring the present demand for service by the street or highway.
4. Evaluating the present traffic flow with respect to the existing street or highway
system.