Annual average daily traffic

Annual average daily traffic, abbrevated AADT, is a measure used primarily in transportation planning and transportation engineering. 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. It is also sometimes reported as "average annual daily traffic".

Uses

The most important use of the AADT is for determining the amount of federal funding a state will receive. Each year on June 15th, every state in the United States submits a [http://www.fhwa.dot.gov/ohim/tmguide/tmg2.htm#The%20HPMS%20Sample Highway Performance Monitoring System HPMS] report. The HPMS report contains various information regarding the road segments in the state and only contains a sample size (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.

Data collection

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. A better calculation method is to average the daily traffic for each of the 12 months - MADT Monthly Average Daily Traffic - and take the average of the MADTs. This method is outlined in the [FHWA Traffic Monitoring Guide] [http://www.fhwa.dot.gov/ohim/tmguide/tmg2.htm#Computing%20AADT] . The continuous count method is costly. There are monthly maintenance fees involved and it is expensive to install and purchase the sensors. It can cost money to power the sensors if it is connected to the local power grid. It can cost money to maintain the communication connection whether it is a phone line or an IP address.

The alternative or second technique is called the short count data collection method also know as the coverage count data collection method. The AADT can be estimated 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] [http://www.fhwa.dot.gov/ohim/tmguide/tmg3.htm#hpmsvolume] recommends to perform a short count on a road segment at a minimum of every three years. After collecting the data with a portable traffic counter, the data is converted into an ADT - Average Daily Traffic. This would represent the average day of traffic for the month the data was recorded. Seeing traffic varies throughout the year, with it generally being low in the winter months and high during the summer months, the AADT is estimated by removing this seasonal bias by multiplying the ADT by the Monthly Seasonal Adjustment Factor. Short counts are taken either by state agencies, local government, or contractors. For the years when a traffic count is not recording, the AADT is estimated by applying a factor called the Growth Factor. Growth Factors are statistically are determined from historical data of the road segment. If there is no historical data, Growth Factors from similar road segments are used.

External links

* [http://www.crenex.com/trafficcounts Crenex - Traffic Counts + Maps] - Links to traffic maps/counts and DOT departments of all US states
* [http://www.dot.state.fl.us/planning/statistics/trafficdata/AADT/aadt.htm Florida]
* [https://www.nysdot.gov/portal/page/portal/divisions/engineering/applications/traffic-data-viewer New York State - Traffic Data Viewer - interactive map program graphically displays traffic data]
* [http://www.okladot.state.ok.us/hqdiv/p-r-div/maps/aadt/index.htm Oklahoma]
* [http://www.virginiadot.org/info/ct-TrafficCounts.asp Virginia]
* [http://www.fhwa.dot.gov/ohim/tmguide/ FHWA Traffic Monitoring Guide]


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