Annual average daily traffic
Annual average daily traffic, abbreviated AADT, is a measure used primarily in
AADT is the standard measurement for vehicle traffic load on a section of road, and the basis for some decisions regarding
Uses
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's department of transportation (DOT) submits a Highway Performance Monitoring System (HPMS) report.[4] 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, National Highways, and the Department for Transport to forecast maintenance needs and expenditure.[5]
Data collection
To measure AADT on individual road segments, traffic data is collected by an automated
While providing the most accurate AADT, installing and maintaining continuous count stations method is costly. Most public 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. The FHWA Traffic Monitoring Guide[7] 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.
Similar measures
- 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 (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.[8]
References
- S2CID 13044779.
- ^ Gary A. Davis (2007). "Accuracy of Estimates of Mean Daily Traffic: A Review". Archived from the original on 2012-07-16. Retrieved 2011-10-15.
- Ontario Ministry of Transportation. Retrieved 2023-03-21.
- ^ "Traffic Monitoring Guide - Policy | Federal Highway Administration".
- ^ DfT Road Traffic Statistics https://roadtraffic.dft.gov.uk/about
- ^ AASHTO Guidelines for Traffic Data Programs. American Association of State Highway and Transportation Officials. 1992.
- ^ a b "Traffic Monitoring Guide - Policy | Federal Highway Administration". www.fhwa.dot.gov.
- ^ "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.
The 1992 Edition of the AASHTO Guidelines is out of date. The current edition is from 2018. 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.