Annual average daily traffic, abbreviated AADT, is a measure used
primarily in transportation planning and transportation engineering.
Traditionally, it is the total volume of vehicle traffic of a highway
or road for a year divided by 365 days. AADT is a useful and simple
measurement of how busy the road is. Newer advances from traffic data
providers are now providing AADT by side of the road, by day of week
and by time of day.
2 Data collection
3 Annual Average Weekday Traffic (AAWT)
4 Average summer daily traffic
5 Average Daily Traffic
7 External links
Highway 401 in Ontario, Canada, has an AADT of over 400,000 in some
sections of Toronto.
One of the most important uses of AADT is for determining funding for
the maintenance and improvement of highways.
In the United States the amount of federal funding a state will
receive is related to the total traffic measured across its highway
network. Each year on June 15, every state in the United States
Highway Performance Monitoring System HPMS report. The HPMS
report contains various information regarding the road segments in the
state based on a sample (not all of the road segments) of the road
segments. In the report, the AADT is converted to vehicle miles
traveled (VMT). VMT is the AADT multiplied by the length of the road
segment. To determine the amount of traffic a state has, the AADT
cannot be summed for all road segments since an AADT is a rate. The
VMT is summed and is used as an indicator of the amount of traffic a
state has. For federal-funding, formulas are applied to include the
VMT and other highway statistics.
In the United Kingdom AADT is one of a number of measures of traffic
used by local highway authorities, Highways England and the Department
for Transport to forecast maintenance needs and expenditure.
A traffic counter on BIA
Road J-9 in the United States
To measure AADT on individual road segments, traffic data is collected
either by an automated traffic counter or hiring an observer to record
traffic. There are two different techniques of measuring the AADTs for
road segments. One technique is called continuous count data
collection method. This is where sensors are permanently embedded into
a road and traffic data is measured all 365 days. The AADT would be
the sum of the total traffic for the entire year divided by 365 days.
There is a problem with calculating the AADT with this method. The
continuous count equipment is not operating for the full 365 days due
to being shut down for maintenance or repair. Because of this,
seasonal or day-of-week biases might skew the calculated AADT. In
1992, AASHTO released the AASHTO Guidelines for Traffic Data
Programs, which identified a way to produce an AADT without
seasonal or day-of-week biases by creating an "average of averages."
For every month and day-of-week, a Monthly Average Day of Week (MADW)
is calculated (84 per year). Each day-of-week's MADW is then
calculated across months to calculate an Annual Average Day of Week
(AADW) (7 per year). Finally, the AADWs are averaged to calculate an
AADT. The United States Federal
Highway Administration (FHWA) has
adopted this method as the preferred method in the [FHWA Traffic
While providing the most accurate AADT, installing and maintaining
continuous count stations method is costly. Most agencies are only
able to monitor a very small percentage of the roadway using this
method. Most AADTs are generated using short-term data collection
methods sometimes known as the coverage count data collection method.
Traffic is collected with portable sensors that are attached to the
road and record traffic data typically for 2 – 14 days. These are
typically pneumatic road tubes although other more expensive
technology such as radar, laser, or sonar exist. After recording the
traffic data, the traffic counts on the same road segment are taken
again in another three years. FHWA Traffic Monitoring Guide 
recommends performing a short count on a road segment at a minimum of
every three years. There are many methods used to calculate an AADT
from a short-term count, but most methods attempt to remove seasonal
and day-of-week biases during the collection period by applying
factors created from associated continuous counters. Short counts are
taken either by state agencies, local government, or contractors.
For the years when a traffic count is not recorded, the AADT is often
estimated by applying a factor called the Growth Factor. Growth
Factors are statistically determined from historical data of the road
segment. If there is no historical data, Growth Factors from similar
road segments are used.
Annual Average Weekday Traffic (AAWT)
Annual average weekday traffic (AAWT) is similar to AADT but only
includes Monday to Friday data. Public holidays are often excluded
from the AAWT calculation.
Average summer daily traffic
Average summer daily traffic (abbreviated to ASDT) is a similar
measure to the annual average daily traffic. Data collecting methods
of the two are exactly the same, however the ASDT data is collected
during summer only. The measure is useful in areas where there are
significant seasonal traffic volumes carried by a given road.
Average Daily Traffic
Average daily traffic or ADT, and sometimes also mean daily traffic,
is the average number of vehicles two-way passing a specific point in
a 24-hour period, normally measured throughout a year. ADT is not as
highly referred to as the engineering standard of AADT which is the
standard measurement for vehicle traffic load on a section of road,
and the basis for most decisions regarding transport planning, or to
the environmental hazards of pollution related to road
^ Ontario Ministry of Transportation. Traffic Volumes. 2010. Accessed
^ AASHTO Guidelines for Traffic Data Programs. American Association of
Highway and Transportation Officials. 1992.
^ "Traffic counting on the roadways of Croatia in 2009 - digest"
(PDF). Hrvatske ceste. May 1, 2010. Archived from the original (PDF)
on July 21, 2011.
^ Gauderman, W James; et al. (2005). "Childhood Asthma and Exposure to
Traffic and Nitrogen Dioxide".
^ Gary A. Davis (2007). "Accuracy of Estimates of Mean Daily Traffic:
A Review". Archived from the original on 2012-07-16.
The 1992 Edition of the AASHTO Guidelines is out of date. The current
edition is from 2009. The Gary Davis article was published in
Transportation Research Record 1593, 1997. the date currently shown in
the article is the date of an on-line posting.
New York State - Traffic Data Viewer - interactive map program
graphically displays traffic data
FHWA Traffic Monitoring Guide
New Zealand State